Move hrtf.cpp/h to core

1 files changed, 1447 insertions, 0 deletions

diff --git a/core/hrtf.cpp b/core/hrtf.cpp
new file mode 100644
index 00000000..0a065be2
--- /dev/null
+++ b/core/hrtf.cpp
@@ -0,0 +1,1447 @@
+
+#include "config.h"
+
+#include "hrtf.h"
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <cctype>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+#include <functional>
+#include <fstream>
+#include <iterator>
+#include <memory>
+#include <mutex>
+#include <new>
+#include <numeric>
+#include <type_traits>
+#include <utility>
+
+#include "albit.h"
+#include "albyte.h"
+#include "alfstream.h"
+#include "almalloc.h"
+#include "alnumeric.h"
+#include "aloptional.h"
+#include "alspan.h"
+#include "ambidefs.h"
+#include "filters/splitter.h"
+#include "helpers.h"
+#include "logging.h"
+#include "math_defs.h"
+#include "opthelpers.h"
+#include "polyphase_resampler.h"
+
+
+namespace {
+
+struct HrtfEntry {
+    std::string mDispName;
+    std::string mFilename;
+};
+
+struct LoadedHrtf {
+    std::string mFilename;
+    std::unique_ptr<HrtfStore> mEntry;
+};
+
+/* Data set limits must be the same as or more flexible than those defined in
+ * the makemhr utility.
+ */
+constexpr uint MinFdCount{1};
+constexpr uint MaxFdCount{16};
+
+constexpr uint MinFdDistance{50};
+constexpr uint MaxFdDistance{2500};
+
+constexpr uint MinEvCount{5};
+constexpr uint MaxEvCount{181};
+
+constexpr uint MinAzCount{1};
+constexpr uint MaxAzCount{255};
+
+constexpr uint MaxHrirDelay{HrtfHistoryLength - 1};
+
+constexpr uint HrirDelayFracBits{2};
+constexpr uint HrirDelayFracOne{1 << HrirDelayFracBits};
+constexpr uint HrirDelayFracHalf{HrirDelayFracOne >> 1};
+
+static_assert(MaxHrirDelay*HrirDelayFracOne < 256, "MAX_HRIR_DELAY or DELAY_FRAC too large");
+
+constexpr char magicMarker00[8]{'M','i','n','P','H','R','0','0'};
+constexpr char magicMarker01[8]{'M','i','n','P','H','R','0','1'};
+constexpr char magicMarker02[8]{'M','i','n','P','H','R','0','2'};
+constexpr char magicMarker03[8]{'M','i','n','P','H','R','0','3'};
+
+/* First value for pass-through coefficients (remaining are 0), used for omni-
+ * directional sounds. */
+constexpr float PassthruCoeff{0.707106781187f/*sqrt(0.5)*/};
+
+std::mutex LoadedHrtfLock;
+al::vector<LoadedHrtf> LoadedHrtfs;
+
+std::mutex EnumeratedHrtfLock;
+al::vector<HrtfEntry> EnumeratedHrtfs;
+
+
+class databuf final : public std::streambuf {
+    int_type underflow() override
+    { return traits_type::eof(); }
+
+    pos_type seekoff(off_type offset, std::ios_base::seekdir whence, std::ios_base::openmode mode) override
+    {
+        if((mode&std::ios_base::out) || !(mode&std::ios_base::in))
+            return traits_type::eof();
+
+        char_type *cur;
+        switch(whence)
+        {
+            case std::ios_base::beg:
+                if(offset < 0 || offset > egptr()-eback())
+                    return traits_type::eof();
+                cur = eback() + offset;
+                break;
+
+            case std::ios_base::cur:
+                if((offset >= 0 && offset > egptr()-gptr()) ||
+                   (offset < 0 && -offset > gptr()-eback()))
+                    return traits_type::eof();
+                cur = gptr() + offset;
+                break;
+
+            case std::ios_base::end:
+                if(offset > 0 || -offset > egptr()-eback())
+                    return traits_type::eof();
+                cur = egptr() + offset;
+                break;
+
+            default:
+                return traits_type::eof();
+        }
+
+        setg(eback(), cur, egptr());
+        return cur - eback();
+    }
+
+    pos_type seekpos(pos_type pos, std::ios_base::openmode mode) override
+    {
+        // Simplified version of seekoff
+        if((mode&std::ios_base::out) || !(mode&std::ios_base::in))
+            return traits_type::eof();
+
+        if(pos < 0 || pos > egptr()-eback())
+            return traits_type::eof();
+
+        setg(eback(), eback() + static_cast<size_t>(pos), egptr());
+        return pos;
+    }
+
+public:
+    databuf(const char_type *start_, const char_type *end_) noexcept
+    {
+        setg(const_cast<char_type*>(start_), const_cast<char_type*>(start_),
+             const_cast<char_type*>(end_));
+    }
+};
+
+class idstream final : public std::istream {
+    databuf mStreamBuf;
+
+public:
+    idstream(const char *start_, const char *end_)
+      : std::istream{nullptr}, mStreamBuf{start_, end_}
+    { init(&mStreamBuf); }
+};
+
+
+struct IdxBlend { uint idx; float blend; };
+/* Calculate the elevation index given the polar elevation in radians. This
+ * will return an index between 0 and (evcount - 1).
+ */
+IdxBlend CalcEvIndex(uint evcount, float ev)
+{
+    ev = (al::MathDefs<float>::Pi()*0.5f + ev) * static_cast<float>(evcount-1) /
+        al::MathDefs<float>::Pi();
+    uint idx{float2uint(ev)};
+
+    return IdxBlend{minu(idx, evcount-1), ev-static_cast<float>(idx)};
+}
+
+/* Calculate the azimuth index given the polar azimuth in radians. This will
+ * return an index between 0 and (azcount - 1).
+ */
+IdxBlend CalcAzIndex(uint azcount, float az)
+{
+    az = (al::MathDefs<float>::Tau()+az) * static_cast<float>(azcount) /
+        al::MathDefs<float>::Tau();
+    uint idx{float2uint(az)};
+
+    return IdxBlend{idx%azcount, az-static_cast<float>(idx)};
+}
+
+} // namespace
+
+
+/* Calculates static HRIR coefficients and delays for the given polar elevation
+ * and azimuth in radians. The coefficients are normalized.
+ */
+void GetHrtfCoeffs(const HrtfStore *Hrtf, float elevation, float azimuth, float distance,
+    float spread, HrirArray &coeffs, const al::span<uint,2> delays)
+{
+    const float dirfact{1.0f - (spread / al::MathDefs<float>::Tau())};
+
+    const auto *field = Hrtf->field;
+    const auto *field_end = field + Hrtf->fdCount-1;
+    size_t ebase{0};
+    while(distance < field->distance && field != field_end)
+    {
+        ebase += field->evCount;
+        ++field;
+    }
+
+    /* Calculate the elevation indices. */
+    const auto elev0 = CalcEvIndex(field->evCount, elevation);
+    const size_t elev1_idx{minu(elev0.idx+1, field->evCount-1)};
+    const size_t ir0offset{Hrtf->elev[ebase + elev0.idx].irOffset};
+    const size_t ir1offset{Hrtf->elev[ebase + elev1_idx].irOffset};
+
+    /* Calculate azimuth indices. */
+    const auto az0 = CalcAzIndex(Hrtf->elev[ebase + elev0.idx].azCount, azimuth);
+    const auto az1 = CalcAzIndex(Hrtf->elev[ebase + elev1_idx].azCount, azimuth);
+
+    /* Calculate the HRIR indices to blend. */
+    const size_t idx[4]{
+        ir0offset + az0.idx,
+        ir0offset + ((az0.idx+1) % Hrtf->elev[ebase + elev0.idx].azCount),
+        ir1offset + az1.idx,
+        ir1offset + ((az1.idx+1) % Hrtf->elev[ebase + elev1_idx].azCount)
+    };
+
+    /* Calculate bilinear blending weights, attenuated according to the
+     * directional panning factor.
+     */
+    const float blend[4]{
+        (1.0f-elev0.blend) * (1.0f-az0.blend) * dirfact,
+        (1.0f-elev0.blend) * (     az0.blend) * dirfact,
+        (     elev0.blend) * (1.0f-az1.blend) * dirfact,
+        (     elev0.blend) * (     az1.blend) * dirfact
+    };
+
+    /* Calculate the blended HRIR delays. */
+    float d{Hrtf->delays[idx[0]][0]*blend[0] + Hrtf->delays[idx[1]][0]*blend[1] +
+        Hrtf->delays[idx[2]][0]*blend[2] + Hrtf->delays[idx[3]][0]*blend[3]};
+    delays[0] = fastf2u(d * float{1.0f/HrirDelayFracOne});
+    d = Hrtf->delays[idx[0]][1]*blend[0] + Hrtf->delays[idx[1]][1]*blend[1] +
+        Hrtf->delays[idx[2]][1]*blend[2] + Hrtf->delays[idx[3]][1]*blend[3];
+    delays[1] = fastf2u(d * float{1.0f/HrirDelayFracOne});
+
+    /* Calculate the blended HRIR coefficients. */
+    float *coeffout{al::assume_aligned<16>(&coeffs[0][0])};
+    coeffout[0] = PassthruCoeff * (1.0f-dirfact);
+    coeffout[1] = PassthruCoeff * (1.0f-dirfact);
+    std::fill_n(coeffout+2, size_t{HrirLength-1}*2, 0.0f);
+    for(size_t c{0};c < 4;c++)
+    {
+        const float *srccoeffs{al::assume_aligned<16>(Hrtf->coeffs[idx[c]][0].data())};
+        const float mult{blend[c]};
+        auto blend_coeffs = [mult](const float src, const float coeff) noexcept -> float
+        { return src*mult + coeff; };
+        std::transform(srccoeffs, srccoeffs + HrirLength*2, coeffout, coeffout, blend_coeffs);
+    }
+}
+
+
+std::unique_ptr<DirectHrtfState> DirectHrtfState::Create(size_t num_chans)
+{ return std::unique_ptr<DirectHrtfState>{new(FamCount(num_chans)) DirectHrtfState{num_chans}}; }
+
+void DirectHrtfState::build(const HrtfStore *Hrtf, const uint irSize,
+    const al::span<const AngularPoint> AmbiPoints, const float (*AmbiMatrix)[MaxAmbiChannels],
+    const float XOverFreq, const al::span<const float,MaxAmbiOrder+1> AmbiOrderHFGain)
+{
+    using double2 = std::array<double,2>;
+    struct ImpulseResponse {
+        const ConstHrirSpan hrir;
+        uint ldelay, rdelay;
+    };
+
+    const double xover_norm{double{XOverFreq} / Hrtf->sampleRate};
+    for(size_t i{0};i < mChannels.size();++i)
+    {
+        const size_t order{AmbiIndex::OrderFromChannel()[i]};
+        mChannels[i].mSplitter.init(static_cast<float>(xover_norm));
+        mChannels[i].mHfScale = AmbiOrderHFGain[order];
+    }
+
+    uint min_delay{HrtfHistoryLength*HrirDelayFracOne}, max_delay{0};
+    al::vector<ImpulseResponse> impres; impres.reserve(AmbiPoints.size());
+    auto calc_res = [Hrtf,&max_delay,&min_delay](const AngularPoint &pt) -> ImpulseResponse
+    {
+        auto &field = Hrtf->field[0];
+        const auto elev0 = CalcEvIndex(field.evCount, pt.Elev.value);
+        const size_t elev1_idx{minu(elev0.idx+1, field.evCount-1)};
+        const size_t ir0offset{Hrtf->elev[elev0.idx].irOffset};
+        const size_t ir1offset{Hrtf->elev[elev1_idx].irOffset};
+
+        const auto az0 = CalcAzIndex(Hrtf->elev[elev0.idx].azCount, pt.Azim.value);
+        const auto az1 = CalcAzIndex(Hrtf->elev[elev1_idx].azCount, pt.Azim.value);
+
+        const size_t idx[4]{
+            ir0offset + az0.idx,
+            ir0offset + ((az0.idx+1) % Hrtf->elev[elev0.idx].azCount),
+            ir1offset + az1.idx,
+            ir1offset + ((az1.idx+1) % Hrtf->elev[elev1_idx].azCount)
+        };
+
+        const std::array<double,4> blend{{
+            (1.0-elev0.blend) * (1.0-az0.blend),
+            (1.0-elev0.blend) * (    az0.blend),
+            (    elev0.blend) * (1.0-az1.blend),
+            (    elev0.blend) * (    az1.blend)
+        }};
+
+        /* The largest blend factor serves as the closest HRIR. */
+        const size_t irOffset{idx[std::max_element(blend.begin(), blend.end()) - blend.begin()]};
+        ImpulseResponse res{Hrtf->coeffs[irOffset],
+            Hrtf->delays[irOffset][0], Hrtf->delays[irOffset][1]};
+
+        min_delay = minu(min_delay, minu(res.ldelay, res.rdelay));
+        max_delay = maxu(max_delay, maxu(res.ldelay, res.rdelay));
+
+        return res;
+    };
+    std::transform(AmbiPoints.begin(), AmbiPoints.end(), std::back_inserter(impres), calc_res);
+    auto hrir_delay_round = [](const uint d) noexcept -> uint
+    { return (d+HrirDelayFracHalf) >> HrirDelayFracBits; };
+
+    TRACE("Min delay: %.2f, max delay: %.2f, FIR length: %u\n",
+        min_delay/double{HrirDelayFracOne}, max_delay/double{HrirDelayFracOne}, irSize);
+
+    const bool per_hrir_min{mChannels.size() > AmbiChannelsFromOrder(1)};
+    auto tmpres = al::vector<std::array<double2,HrirLength>>(mChannels.size());
+    max_delay = 0;
+    for(size_t c{0u};c < AmbiPoints.size();++c)
+    {
+        const ConstHrirSpan hrir{impres[c].hrir};
+        const uint base_delay{per_hrir_min ? minu(impres[c].ldelay, impres[c].rdelay) : min_delay};
+        const uint ldelay{hrir_delay_round(impres[c].ldelay - base_delay)};
+        const uint rdelay{hrir_delay_round(impres[c].rdelay - base_delay)};
+        max_delay = maxu(max_delay, maxu(impres[c].ldelay, impres[c].rdelay) - base_delay);
+
+        for(size_t i{0u};i < mChannels.size();++i)
+        {
+            const double mult{AmbiMatrix[c][i]};
+            const size_t numirs{HrirLength - maxz(ldelay, rdelay)};
+            size_t lidx{ldelay}, ridx{rdelay};
+            for(size_t j{0};j < numirs;++j)
+            {
+                tmpres[i][lidx++][0] += hrir[j][0] * mult;
+                tmpres[i][ridx++][1] += hrir[j][1] * mult;
+            }
+        }
+    }
+    impres.clear();
+
+    for(size_t i{0u};i < mChannels.size();++i)
+    {
+        auto copy_arr = [](const double2 &in) noexcept -> float2
+        { return float2{{static_cast<float>(in[0]), static_cast<float>(in[1])}}; };
+        std::transform(tmpres[i].cbegin(), tmpres[i].cend(), mChannels[i].mCoeffs.begin(),
+            copy_arr);
+    }
+    tmpres.clear();
+
+    const uint max_length{minu(hrir_delay_round(max_delay) + irSize, HrirLength)};
+    TRACE("New max delay: %.2f, FIR length: %u\n", max_delay/double{HrirDelayFracOne},
+        max_length);
+    mIrSize = max_length;
+}
+
+
+namespace {
+
+std::unique_ptr<HrtfStore> CreateHrtfStore(uint rate, ushort irSize,
+    const al::span<const HrtfStore::Field> fields,
+    const al::span<const HrtfStore::Elevation> elevs, const HrirArray *coeffs,
+    const ubyte2 *delays, const char *filename)
+{
+    std::unique_ptr<HrtfStore> Hrtf;
+
+    const size_t irCount{size_t{elevs.back().azCount} + elevs.back().irOffset};
+    size_t total{sizeof(HrtfStore)};
+    total  = RoundUp(total, alignof(HrtfStore::Field)); /* Align for field infos */
+    total += sizeof(HrtfStore::Field)*fields.size();
+    total  = RoundUp(total, alignof(HrtfStore::Elevation)); /* Align for elevation infos */
+    total += sizeof(Hrtf->elev[0])*elevs.size();
+    total  = RoundUp(total, 16); /* Align for coefficients using SIMD */
+    total += sizeof(Hrtf->coeffs[0])*irCount;
+    total += sizeof(Hrtf->delays[0])*irCount;
+
+    Hrtf.reset(new (al_calloc(16, total)) HrtfStore{});
+    if(!Hrtf)
+        ERR("Out of memory allocating storage for %s.\n", filename);
+    else
+    {
+        InitRef(Hrtf->mRef, 1u);
+        Hrtf->sampleRate = rate;
+        Hrtf->irSize = irSize;
+        Hrtf->fdCount = static_cast<uint>(fields.size());
+
+        /* Set up pointers to storage following the main HRTF struct. */
+        char *base = reinterpret_cast<char*>(Hrtf.get());
+        size_t offset{sizeof(HrtfStore)};
+
+        offset = RoundUp(offset, alignof(HrtfStore::Field)); /* Align for field infos */
+        auto field_ = reinterpret_cast<HrtfStore::Field*>(base + offset);
+        offset += sizeof(field_[0])*fields.size();
+
+        offset = RoundUp(offset, alignof(HrtfStore::Elevation)); /* Align for elevation infos */
+        auto elev_ = reinterpret_cast<HrtfStore::Elevation*>(base + offset);
+        offset += sizeof(elev_[0])*elevs.size();
+
+        offset = RoundUp(offset, 16); /* Align for coefficients using SIMD */
+        auto coeffs_ = reinterpret_cast<HrirArray*>(base + offset);
+        offset += sizeof(coeffs_[0])*irCount;
+
+        auto delays_ = reinterpret_cast<ubyte2*>(base + offset);
+        offset += sizeof(delays_[0])*irCount;
+
+        assert(offset == total);
+
+        /* Copy input data to storage. */
+        std::copy(fields.cbegin(), fields.cend(), field_);
+        std::copy(elevs.cbegin(), elevs.cend(), elev_);
+        std::copy_n(coeffs, irCount, coeffs_);
+        std::copy_n(delays, irCount, delays_);
+
+        /* Finally, assign the storage pointers. */
+        Hrtf->field = field_;
+        Hrtf->elev = elev_;
+        Hrtf->coeffs = coeffs_;
+        Hrtf->delays = delays_;
+    }
+
+    return Hrtf;
+}
+
+void MirrorLeftHrirs(const al::span<const HrtfStore::Elevation> elevs, HrirArray *coeffs,
+    ubyte2 *delays)
+{
+    for(const auto &elev : elevs)
+    {
+        const ushort evoffset{elev.irOffset};
+        const ushort azcount{elev.azCount};
+        for(size_t j{0};j < azcount;j++)
+        {
+            const size_t lidx{evoffset + j};
+            const size_t ridx{evoffset + ((azcount-j) % azcount)};
+
+            const size_t irSize{coeffs[ridx].size()};
+            for(size_t k{0};k < irSize;k++)
+                coeffs[ridx][k][1] = coeffs[lidx][k][0];
+            delays[ridx][1] = delays[lidx][0];
+        }
+    }
+}
+
+
+template<typename T, size_t num_bits=sizeof(T)*8>
+inline T readle(std::istream &data)
+{
+    static_assert((num_bits&7) == 0, "num_bits must be a multiple of 8");
+    static_assert(num_bits <= sizeof(T)*8, "num_bits is too large for the type");
+
+    T ret{};
+    if_constexpr(al::endian::native == al::endian::little)
+    {
+        if(!data.read(reinterpret_cast<char*>(&ret), num_bits/8))
+            return static_cast<T>(EOF);
+    }
+    else
+    {
+        al::byte b[sizeof(T)]{};
+        if(!data.read(reinterpret_cast<char*>(b), num_bits/8))
+            return static_cast<T>(EOF);
+        std::reverse_copy(std::begin(b), std::end(b), reinterpret_cast<al::byte*>(&ret));
+    }
+
+    if_constexpr(std::is_signed<T>::value && num_bits < sizeof(T)*8)
+    {
+        constexpr auto signbit = static_cast<T>(1u << (num_bits-1));
+        return static_cast<T>((ret^signbit) - signbit);
+    }
+    return ret;
+}
+
+template<>
+inline uint8_t readle<uint8_t,8>(std::istream &data)
+{ return static_cast<uint8_t>(data.get()); }
+
+
+std::unique_ptr<HrtfStore> LoadHrtf00(std::istream &data, const char *filename)
+{
+    uint rate{readle<uint32_t>(data)};
+    ushort irCount{readle<uint16_t>(data)};
+    ushort irSize{readle<uint16_t>(data)};
+    ubyte evCount{readle<uint8_t>(data)};
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+
+    if(irSize < MinIrLength || irSize > HrirLength)
+    {
+        ERR("Unsupported HRIR size, irSize=%d (%d to %d)\n", irSize, MinIrLength, HrirLength);
+        return nullptr;
+    }
+    if(evCount < MinEvCount || evCount > MaxEvCount)
+    {
+        ERR("Unsupported elevation count: evCount=%d (%d to %d)\n",
+            evCount, MinEvCount, MaxEvCount);
+        return nullptr;
+    }
+
+    auto elevs = al::vector<HrtfStore::Elevation>(evCount);
+    for(auto &elev : elevs)
+        elev.irOffset = readle<uint16_t>(data);
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+    for(size_t i{1};i < evCount;i++)
+    {
+        if(elevs[i].irOffset <= elevs[i-1].irOffset)
+        {
+            ERR("Invalid evOffset: evOffset[%zu]=%d (last=%d)\n", i, elevs[i].irOffset,
+                elevs[i-1].irOffset);
+            return nullptr;
+        }
+    }
+    if(irCount <= elevs.back().irOffset)
+    {
+        ERR("Invalid evOffset: evOffset[%zu]=%d (irCount=%d)\n",
+            elevs.size()-1, elevs.back().irOffset, irCount);
+        return nullptr;
+    }
+
+    for(size_t i{1};i < evCount;i++)
+    {
+        elevs[i-1].azCount = static_cast<ushort>(elevs[i].irOffset - elevs[i-1].irOffset);
+        if(elevs[i-1].azCount < MinAzCount || elevs[i-1].azCount > MaxAzCount)
+        {
+            ERR("Unsupported azimuth count: azCount[%zd]=%d (%d to %d)\n",
+                i-1, elevs[i-1].azCount, MinAzCount, MaxAzCount);
+            return nullptr;
+        }
+    }
+    elevs.back().azCount = static_cast<ushort>(irCount - elevs.back().irOffset);
+    if(elevs.back().azCount < MinAzCount || elevs.back().azCount > MaxAzCount)
+    {
+        ERR("Unsupported azimuth count: azCount[%zu]=%d (%d to %d)\n",
+            elevs.size()-1, elevs.back().azCount, MinAzCount, MaxAzCount);
+        return nullptr;
+    }
+
+    auto coeffs = al::vector<HrirArray>(irCount, HrirArray{});
+    auto delays = al::vector<ubyte2>(irCount);
+    for(auto &hrir : coeffs)
+    {
+        for(auto &val : al::span<float2>{hrir.data(), irSize})
+            val[0] = readle<int16_t>(data) / 32768.0f;
+    }
+    for(auto &val : delays)
+        val[0] = readle<uint8_t>(data);
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+    for(size_t i{0};i < irCount;i++)
+    {
+        if(delays[i][0] > MaxHrirDelay)
+        {
+            ERR("Invalid delays[%zd]: %d (%d)\n", i, delays[i][0], MaxHrirDelay);
+            return nullptr;
+        }
+        delays[i][0] <<= HrirDelayFracBits;
+    }
+
+    /* Mirror the left ear responses to the right ear. */
+    MirrorLeftHrirs({elevs.data(), elevs.size()}, coeffs.data(), delays.data());
+
+    const HrtfStore::Field field[1]{{0.0f, evCount}};
+    return CreateHrtfStore(rate, irSize, field, {elevs.data(), elevs.size()}, coeffs.data(),
+        delays.data(), filename);
+}
+
+std::unique_ptr<HrtfStore> LoadHrtf01(std::istream &data, const char *filename)
+{
+    uint rate{readle<uint32_t>(data)};
+    ushort irSize{readle<uint8_t>(data)};
+    ubyte evCount{readle<uint8_t>(data)};
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+
+    if(irSize < MinIrLength || irSize > HrirLength)
+    {
+        ERR("Unsupported HRIR size, irSize=%d (%d to %d)\n", irSize, MinIrLength, HrirLength);
+        return nullptr;
+    }
+    if(evCount < MinEvCount || evCount > MaxEvCount)
+    {
+        ERR("Unsupported elevation count: evCount=%d (%d to %d)\n",
+            evCount, MinEvCount, MaxEvCount);
+        return nullptr;
+    }
+
+    auto elevs = al::vector<HrtfStore::Elevation>(evCount);
+    for(auto &elev : elevs)
+        elev.azCount = readle<uint8_t>(data);
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+    for(size_t i{0};i < evCount;++i)
+    {
+        if(elevs[i].azCount < MinAzCount || elevs[i].azCount > MaxAzCount)
+        {
+            ERR("Unsupported azimuth count: azCount[%zd]=%d (%d to %d)\n", i, elevs[i].azCount,
+                MinAzCount, MaxAzCount);
+            return nullptr;
+        }
+    }
+
+    elevs[0].irOffset = 0;
+    for(size_t i{1};i < evCount;i++)
+        elevs[i].irOffset = static_cast<ushort>(elevs[i-1].irOffset + elevs[i-1].azCount);
+    const ushort irCount{static_cast<ushort>(elevs.back().irOffset + elevs.back().azCount)};
+
+    auto coeffs = al::vector<HrirArray>(irCount, HrirArray{});
+    auto delays = al::vector<ubyte2>(irCount);
+    for(auto &hrir : coeffs)
+    {
+        for(auto &val : al::span<float2>{hrir.data(), irSize})
+            val[0] = readle<int16_t>(data) / 32768.0f;
+    }
+    for(auto &val : delays)
+        val[0] = readle<uint8_t>(data);
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+    for(size_t i{0};i < irCount;i++)
+    {
+        if(delays[i][0] > MaxHrirDelay)
+        {
+            ERR("Invalid delays[%zd]: %d (%d)\n", i, delays[i][0], MaxHrirDelay);
+            return nullptr;
+        }
+        delays[i][0] <<= HrirDelayFracBits;
+    }
+
+    /* Mirror the left ear responses to the right ear. */
+    MirrorLeftHrirs({elevs.data(), elevs.size()}, coeffs.data(), delays.data());
+
+    const HrtfStore::Field field[1]{{0.0f, evCount}};
+    return CreateHrtfStore(rate, irSize, field, {elevs.data(), elevs.size()}, coeffs.data(),
+        delays.data(), filename);
+}
+
+std::unique_ptr<HrtfStore> LoadHrtf02(std::istream &data, const char *filename)
+{
+    constexpr ubyte SampleType_S16{0};
+    constexpr ubyte SampleType_S24{1};
+    constexpr ubyte ChanType_LeftOnly{0};
+    constexpr ubyte ChanType_LeftRight{1};
+
+    uint rate{readle<uint32_t>(data)};
+    ubyte sampleType{readle<uint8_t>(data)};
+    ubyte channelType{readle<uint8_t>(data)};
+    ushort irSize{readle<uint8_t>(data)};
+    ubyte fdCount{readle<uint8_t>(data)};
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+
+    if(sampleType > SampleType_S24)
+    {
+        ERR("Unsupported sample type: %d\n", sampleType);
+        return nullptr;
+    }
+    if(channelType > ChanType_LeftRight)
+    {
+        ERR("Unsupported channel type: %d\n", channelType);
+        return nullptr;
+    }
+
+    if(irSize < MinIrLength || irSize > HrirLength)
+    {
+        ERR("Unsupported HRIR size, irSize=%d (%d to %d)\n", irSize, MinIrLength, HrirLength);
+        return nullptr;
+    }
+    if(fdCount < 1 || fdCount > MaxFdCount)
+    {
+        ERR("Unsupported number of field-depths: fdCount=%d (%d to %d)\n", fdCount, MinFdCount,
+            MaxFdCount);
+        return nullptr;
+    }
+
+    auto fields = al::vector<HrtfStore::Field>(fdCount);
+    auto elevs = al::vector<HrtfStore::Elevation>{};
+    for(size_t f{0};f < fdCount;f++)
+    {
+        const ushort distance{readle<uint16_t>(data)};
+        const ubyte evCount{readle<uint8_t>(data)};
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        if(distance < MinFdDistance || distance > MaxFdDistance)
+        {
+            ERR("Unsupported field distance[%zu]=%d (%d to %d millimeters)\n", f, distance,
+                MinFdDistance, MaxFdDistance);
+            return nullptr;
+        }
+        if(evCount < MinEvCount || evCount > MaxEvCount)
+        {
+            ERR("Unsupported elevation count: evCount[%zu]=%d (%d to %d)\n", f, evCount,
+                MinEvCount, MaxEvCount);
+            return nullptr;
+        }
+
+        fields[f].distance = distance / 1000.0f;
+        fields[f].evCount = evCount;
+        if(f > 0 && fields[f].distance <= fields[f-1].distance)
+        {
+            ERR("Field distance[%zu] is not after previous (%f > %f)\n", f, fields[f].distance,
+                fields[f-1].distance);
+            return nullptr;
+        }
+
+        const size_t ebase{elevs.size()};
+        elevs.resize(ebase + evCount);
+        for(auto &elev : al::span<HrtfStore::Elevation>(elevs.data()+ebase, evCount))
+            elev.azCount = readle<uint8_t>(data);
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        for(size_t e{0};e < evCount;e++)
+        {
+            if(elevs[ebase+e].azCount < MinAzCount || elevs[ebase+e].azCount > MaxAzCount)
+            {
+                ERR("Unsupported azimuth count: azCount[%zu][%zu]=%d (%d to %d)\n", f, e,
+                    elevs[ebase+e].azCount, MinAzCount, MaxAzCount);
+                return nullptr;
+            }
+        }
+    }
+
+    elevs[0].irOffset = 0;
+    std::partial_sum(elevs.cbegin(), elevs.cend(), elevs.begin(),
+        [](const HrtfStore::Elevation &last, const HrtfStore::Elevation &cur)
+            -> HrtfStore::Elevation
+        {
+            return HrtfStore::Elevation{cur.azCount,
+                static_cast<ushort>(last.azCount + last.irOffset)};
+        });
+    const auto irTotal = static_cast<ushort>(elevs.back().azCount + elevs.back().irOffset);
+
+    auto coeffs = al::vector<HrirArray>(irTotal, HrirArray{});
+    auto delays = al::vector<ubyte2>(irTotal);
+    if(channelType == ChanType_LeftOnly)
+    {
+        if(sampleType == SampleType_S16)
+        {
+            for(auto &hrir : coeffs)
+            {
+                for(auto &val : al::span<float2>{hrir.data(), irSize})
+                    val[0] = readle<int16_t>(data) / 32768.0f;
+            }
+        }
+        else if(sampleType == SampleType_S24)
+        {
+            for(auto &hrir : coeffs)
+            {
+                for(auto &val : al::span<float2>{hrir.data(), irSize})
+                    val[0] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+            }
+        }
+        for(auto &val : delays)
+            val[0] = readle<uint8_t>(data);
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+        for(size_t i{0};i < irTotal;++i)
+        {
+            if(delays[i][0] > MaxHrirDelay)
+            {
+                ERR("Invalid delays[%zu][0]: %d (%d)\n", i, delays[i][0], MaxHrirDelay);
+                return nullptr;
+            }
+            delays[i][0] <<= HrirDelayFracBits;
+        }
+
+        /* Mirror the left ear responses to the right ear. */
+        MirrorLeftHrirs({elevs.data(), elevs.size()}, coeffs.data(), delays.data());
+    }
+    else if(channelType == ChanType_LeftRight)
+    {
+        if(sampleType == SampleType_S16)
+        {
+            for(auto &hrir : coeffs)
+            {
+                for(auto &val : al::span<float2>{hrir.data(), irSize})
+                {
+                    val[0] = readle<int16_t>(data) / 32768.0f;
+                    val[1] = readle<int16_t>(data) / 32768.0f;
+                }
+            }
+        }
+        else if(sampleType == SampleType_S24)
+        {
+            for(auto &hrir : coeffs)
+            {
+                for(auto &val : al::span<float2>{hrir.data(), irSize})
+                {
+                    val[0] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+                    val[1] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+                }
+            }
+        }
+        for(auto &val : delays)
+        {
+            val[0] = readle<uint8_t>(data);
+            val[1] = readle<uint8_t>(data);
+        }
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        for(size_t i{0};i < irTotal;++i)
+        {
+            if(delays[i][0] > MaxHrirDelay)
+            {
+                ERR("Invalid delays[%zu][0]: %d (%d)\n", i, delays[i][0], MaxHrirDelay);
+                return nullptr;
+            }
+            if(delays[i][1] > MaxHrirDelay)
+            {
+                ERR("Invalid delays[%zu][1]: %d (%d)\n", i, delays[i][1], MaxHrirDelay);
+                return nullptr;
+            }
+            delays[i][0] <<= HrirDelayFracBits;
+            delays[i][1] <<= HrirDelayFracBits;
+        }
+    }
+
+    if(fdCount > 1)
+    {
+        auto fields_ = al::vector<HrtfStore::Field>(fields.size());
+        auto elevs_ = al::vector<HrtfStore::Elevation>(elevs.size());
+        auto coeffs_ = al::vector<HrirArray>(coeffs.size());
+        auto delays_ = al::vector<ubyte2>(delays.size());
+
+        /* Simple reverse for the per-field elements. */
+        std::reverse_copy(fields.cbegin(), fields.cend(), fields_.begin());
+
+        /* Each field has a group of elevations, which each have an azimuth
+         * count. Reverse the order of the groups, keeping the relative order
+         * of per-group azimuth counts.
+         */
+        auto elevs__end = elevs_.end();
+        auto copy_azs = [&elevs,&elevs__end](const ptrdiff_t ebase, const HrtfStore::Field &field)
+            -> ptrdiff_t
+        {
+            auto elevs_src = elevs.begin()+ebase;
+            elevs__end = std::copy_backward(elevs_src, elevs_src+field.evCount, elevs__end);
+            return ebase + field.evCount;
+        };
+        (void)std::accumulate(fields.cbegin(), fields.cend(), ptrdiff_t{0}, copy_azs);
+        assert(elevs_.begin() == elevs__end);
+
+        /* Reestablish the IR offset for each elevation index, given the new
+         * ordering of elevations.
+         */
+        elevs_[0].irOffset = 0;
+        std::partial_sum(elevs_.cbegin(), elevs_.cend(), elevs_.begin(),
+            [](const HrtfStore::Elevation &last, const HrtfStore::Elevation &cur)
+                -> HrtfStore::Elevation
+            {
+                return HrtfStore::Elevation{cur.azCount,
+                    static_cast<ushort>(last.azCount + last.irOffset)};
+            });
+
+        /* Reverse the order of each field's group of IRs. */
+        auto coeffs_end = coeffs_.end();
+        auto delays_end = delays_.end();
+        auto copy_irs = [&elevs,&coeffs,&delays,&coeffs_end,&delays_end](
+            const ptrdiff_t ebase, const HrtfStore::Field &field) -> ptrdiff_t
+        {
+            auto accum_az = [](int count, const HrtfStore::Elevation &elev) noexcept -> int
+            { return count + elev.azCount; };
+            const auto elevs_mid = elevs.cbegin() + ebase;
+            const auto elevs_end = elevs_mid + field.evCount;
+            const int abase{std::accumulate(elevs.cbegin(), elevs_mid, 0, accum_az)};
+            const int num_azs{std::accumulate(elevs_mid, elevs_end, 0, accum_az)};
+
+            coeffs_end = std::copy_backward(coeffs.cbegin() + abase,
+                coeffs.cbegin() + (abase+num_azs), coeffs_end);
+            delays_end = std::copy_backward(delays.cbegin() + abase,
+                delays.cbegin() + (abase+num_azs), delays_end);
+
+            return ebase + field.evCount;
+        };
+        (void)std::accumulate(fields.cbegin(), fields.cend(), ptrdiff_t{0}, copy_irs);
+        assert(coeffs_.begin() == coeffs_end);
+        assert(delays_.begin() == delays_end);
+
+        fields = std::move(fields_);
+        elevs = std::move(elevs_);
+        coeffs = std::move(coeffs_);
+        delays = std::move(delays_);
+    }
+
+    return CreateHrtfStore(rate, irSize, {fields.data(), fields.size()},
+        {elevs.data(), elevs.size()}, coeffs.data(), delays.data(), filename);
+}
+
+std::unique_ptr<HrtfStore> LoadHrtf03(std::istream &data, const char *filename)
+{
+    constexpr ubyte ChanType_LeftOnly{0};
+    constexpr ubyte ChanType_LeftRight{1};
+
+    uint rate{readle<uint32_t>(data)};
+    ubyte channelType{readle<uint8_t>(data)};
+    ushort irSize{readle<uint8_t>(data)};
+    ubyte fdCount{readle<uint8_t>(data)};
+    if(!data || data.eof())
+    {
+        ERR("Failed reading %s\n", filename);
+        return nullptr;
+    }
+
+    if(channelType > ChanType_LeftRight)
+    {
+        ERR("Unsupported channel type: %d\n", channelType);
+        return nullptr;
+    }
+
+    if(irSize < MinIrLength || irSize > HrirLength)
+    {
+        ERR("Unsupported HRIR size, irSize=%d (%d to %d)\n", irSize, MinIrLength, HrirLength);
+        return nullptr;
+    }
+    if(fdCount < 1 || fdCount > MaxFdCount)
+    {
+        ERR("Unsupported number of field-depths: fdCount=%d (%d to %d)\n", fdCount, MinFdCount,
+            MaxFdCount);
+        return nullptr;
+    }
+
+    auto fields = al::vector<HrtfStore::Field>(fdCount);
+    auto elevs = al::vector<HrtfStore::Elevation>{};
+    for(size_t f{0};f < fdCount;f++)
+    {
+        const ushort distance{readle<uint16_t>(data)};
+        const ubyte evCount{readle<uint8_t>(data)};
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        if(distance < MinFdDistance || distance > MaxFdDistance)
+        {
+            ERR("Unsupported field distance[%zu]=%d (%d to %d millimeters)\n", f, distance,
+                MinFdDistance, MaxFdDistance);
+            return nullptr;
+        }
+        if(evCount < MinEvCount || evCount > MaxEvCount)
+        {
+            ERR("Unsupported elevation count: evCount[%zu]=%d (%d to %d)\n", f, evCount,
+                MinEvCount, MaxEvCount);
+            return nullptr;
+        }
+
+        fields[f].distance = distance / 1000.0f;
+        fields[f].evCount = evCount;
+        if(f > 0 && fields[f].distance > fields[f-1].distance)
+        {
+            ERR("Field distance[%zu] is not before previous (%f <= %f)\n", f, fields[f].distance,
+                fields[f-1].distance);
+            return nullptr;
+        }
+
+        const size_t ebase{elevs.size()};
+        elevs.resize(ebase + evCount);
+        for(auto &elev : al::span<HrtfStore::Elevation>(elevs.data()+ebase, evCount))
+            elev.azCount = readle<uint8_t>(data);
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        for(size_t e{0};e < evCount;e++)
+        {
+            if(elevs[ebase+e].azCount < MinAzCount || elevs[ebase+e].azCount > MaxAzCount)
+            {
+                ERR("Unsupported azimuth count: azCount[%zu][%zu]=%d (%d to %d)\n", f, e,
+                    elevs[ebase+e].azCount, MinAzCount, MaxAzCount);
+                return nullptr;
+            }
+        }
+    }
+
+    elevs[0].irOffset = 0;
+    std::partial_sum(elevs.cbegin(), elevs.cend(), elevs.begin(),
+        [](const HrtfStore::Elevation &last, const HrtfStore::Elevation &cur)
+            -> HrtfStore::Elevation
+        {
+            return HrtfStore::Elevation{cur.azCount,
+                static_cast<ushort>(last.azCount + last.irOffset)};
+        });
+    const auto irTotal = static_cast<ushort>(elevs.back().azCount + elevs.back().irOffset);
+
+    auto coeffs = al::vector<HrirArray>(irTotal, HrirArray{});
+    auto delays = al::vector<ubyte2>(irTotal);
+    if(channelType == ChanType_LeftOnly)
+    {
+        for(auto &hrir : coeffs)
+        {
+            for(auto &val : al::span<float2>{hrir.data(), irSize})
+                val[0] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+        }
+        for(auto &val : delays)
+            val[0] = readle<uint8_t>(data);
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+        for(size_t i{0};i < irTotal;++i)
+        {
+            if(delays[i][0] > MaxHrirDelay<<HrirDelayFracBits)
+            {
+                ERR("Invalid delays[%zu][0]: %f (%d)\n", i,
+                    delays[i][0] / float{HrirDelayFracOne}, MaxHrirDelay);
+                return nullptr;
+            }
+        }
+
+        /* Mirror the left ear responses to the right ear. */
+        MirrorLeftHrirs({elevs.data(), elevs.size()}, coeffs.data(), delays.data());
+    }
+    else if(channelType == ChanType_LeftRight)
+    {
+        for(auto &hrir : coeffs)
+        {
+            for(auto &val : al::span<float2>{hrir.data(), irSize})
+            {
+                val[0] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+                val[1] = static_cast<float>(readle<int,24>(data)) / 8388608.0f;
+            }
+        }
+        for(auto &val : delays)
+        {
+            val[0] = readle<uint8_t>(data);
+            val[1] = readle<uint8_t>(data);
+        }
+        if(!data || data.eof())
+        {
+            ERR("Failed reading %s\n", filename);
+            return nullptr;
+        }
+
+        for(size_t i{0};i < irTotal;++i)
+        {
+            if(delays[i][0] > MaxHrirDelay<<HrirDelayFracBits)
+            {
+                ERR("Invalid delays[%zu][0]: %f (%d)\n", i,
+                    delays[i][0] / float{HrirDelayFracOne}, MaxHrirDelay);
+                return nullptr;
+            }
+            if(delays[i][1] > MaxHrirDelay<<HrirDelayFracBits)
+            {
+                ERR("Invalid delays[%zu][1]: %f (%d)\n", i,
+                    delays[i][1] / float{HrirDelayFracOne}, MaxHrirDelay);
+                return nullptr;
+            }
+        }
+    }
+
+    return CreateHrtfStore(rate, irSize, {fields.data(), fields.size()},
+        {elevs.data(), elevs.size()}, coeffs.data(), delays.data(), filename);
+}
+
+
+bool checkName(const std::string &name)
+{
+    auto match_name = [&name](const HrtfEntry &entry) -> bool { return name == entry.mDispName; };
+    auto &enum_names = EnumeratedHrtfs;
+    return std::find_if(enum_names.cbegin(), enum_names.cend(), match_name) != enum_names.cend();
+}
+
+void AddFileEntry(const std::string &filename)
+{
+    /* Check if this file has already been enumerated. */
+    auto enum_iter = std::find_if(EnumeratedHrtfs.cbegin(), EnumeratedHrtfs.cend(),
+        [&filename](const HrtfEntry &entry) -> bool
+        { return entry.mFilename == filename; });
+    if(enum_iter != EnumeratedHrtfs.cend())
+    {
+        TRACE("Skipping duplicate file entry %s\n", filename.c_str());
+        return;
+    }
+
+    /* TODO: Get a human-readable name from the HRTF data (possibly coming in a
+     * format update). */
+    size_t namepos{filename.find_last_of('/')+1};
+    if(!namepos) namepos = filename.find_last_of('\\')+1;
+
+    size_t extpos{filename.find_last_of('.')};
+    if(extpos <= namepos) extpos = std::string::npos;
+
+    const std::string basename{(extpos == std::string::npos) ?
+        filename.substr(namepos) : filename.substr(namepos, extpos-namepos)};
+    std::string newname{basename};
+    int count{1};
+    while(checkName(newname))
+    {
+        newname = basename;
+        newname += " #";
+        newname += std::to_string(++count);
+    }
+    EnumeratedHrtfs.emplace_back(HrtfEntry{newname, filename});
+    const HrtfEntry &entry = EnumeratedHrtfs.back();
+
+    TRACE("Adding file entry \"%s\"\n", entry.mFilename.c_str());
+}
+
+/* Unfortunate that we have to duplicate AddFileEntry to take a memory buffer
+ * for input instead of opening the given filename.
+ */
+void AddBuiltInEntry(const std::string &dispname, uint residx)
+{
+    const std::string filename{'!'+std::to_string(residx)+'_'+dispname};
+
+    auto enum_iter = std::find_if(EnumeratedHrtfs.cbegin(), EnumeratedHrtfs.cend(),
+        [&filename](const HrtfEntry &entry) -> bool
+        { return entry.mFilename == filename; });
+    if(enum_iter != EnumeratedHrtfs.cend())
+    {
+        TRACE("Skipping duplicate file entry %s\n", filename.c_str());
+        return;
+    }
+
+    /* TODO: Get a human-readable name from the HRTF data (possibly coming in a
+     * format update). */
+
+    std::string newname{dispname};
+    int count{1};
+    while(checkName(newname))
+    {
+        newname = dispname;
+        newname += " #";
+        newname += std::to_string(++count);
+    }
+    EnumeratedHrtfs.emplace_back(HrtfEntry{newname, filename});
+    const HrtfEntry &entry = EnumeratedHrtfs.back();
+
+    TRACE("Adding built-in entry \"%s\"\n", entry.mFilename.c_str());
+}
+
+
+#define IDR_DEFAULT_HRTF_MHR 1
+
+#ifndef ALSOFT_EMBED_HRTF_DATA
+
+al::span<const char> GetResource(int /*name*/)
+{ return {}; }
+
+#else
+
+#include "hrtf_default.h"
+
+al::span<const char> GetResource(int name)
+{
+    if(name == IDR_DEFAULT_HRTF_MHR)
+        return {reinterpret_cast<const char*>(hrtf_default), sizeof(hrtf_default)};
+    return {};
+}
+#endif
+
+} // namespace
+
+
+al::vector<std::string> EnumerateHrtf(al::optional<std::string> pathopt)
+{
+    std::lock_guard<std::mutex> _{EnumeratedHrtfLock};
+    EnumeratedHrtfs.clear();
+
+    bool usedefaults{true};
+    if(pathopt)
+    {
+        const char *pathlist{pathopt->c_str()};
+        while(pathlist && *pathlist)
+        {
+            const char *next, *end;
+
+            while(isspace(*pathlist) || *pathlist == ',')
+                pathlist++;
+            if(*pathlist == '\0')
+                continue;
+
+            next = strchr(pathlist, ',');
+            if(next)
+                end = next++;
+            else
+            {
+                end = pathlist + strlen(pathlist);
+                usedefaults = false;
+            }
+
+            while(end != pathlist && isspace(*(end-1)))
+                --end;
+            if(end != pathlist)
+            {
+                const std::string pname{pathlist, end};
+                for(const auto &fname : SearchDataFiles(".mhr", pname.c_str()))
+                    AddFileEntry(fname);
+            }
+
+            pathlist = next;
+        }
+    }
+
+    if(usedefaults)
+    {
+        for(const auto &fname : SearchDataFiles(".mhr", "openal/hrtf"))
+            AddFileEntry(fname);
+
+        if(!GetResource(IDR_DEFAULT_HRTF_MHR).empty())
+            AddBuiltInEntry("Built-In HRTF", IDR_DEFAULT_HRTF_MHR);
+    }
+
+    al::vector<std::string> list;
+    list.reserve(EnumeratedHrtfs.size());
+    for(auto &entry : EnumeratedHrtfs)
+        list.emplace_back(entry.mDispName);
+
+    return list;
+}
+
+HrtfStorePtr GetLoadedHrtf(const std::string &name, const uint devrate)
+{
+    std::lock_guard<std::mutex> _{EnumeratedHrtfLock};
+    auto entry_iter = std::find_if(EnumeratedHrtfs.cbegin(), EnumeratedHrtfs.cend(),
+        [&name](const HrtfEntry &entry) -> bool { return entry.mDispName == name; });
+    if(entry_iter == EnumeratedHrtfs.cend())
+        return nullptr;
+    const std::string &fname = entry_iter->mFilename;
+
+    std::lock_guard<std::mutex> __{LoadedHrtfLock};
+    auto hrtf_lt_fname = [](LoadedHrtf &hrtf, const std::string &filename) -> bool
+    { return hrtf.mFilename < filename; };
+    auto handle = std::lower_bound(LoadedHrtfs.begin(), LoadedHrtfs.end(), fname, hrtf_lt_fname);
+    while(handle != LoadedHrtfs.end() && handle->mFilename == fname)
+    {
+        HrtfStore *hrtf{handle->mEntry.get()};
+        if(hrtf && hrtf->sampleRate == devrate)
+        {
+            hrtf->add_ref();
+            return HrtfStorePtr{hrtf};
+        }
+        ++handle;
+    }
+
+    std::unique_ptr<std::istream> stream;
+    int residx{};
+    char ch{};
+    if(sscanf(fname.c_str(), "!%d%c", &residx, &ch) == 2 && ch == '_')
+    {
+        TRACE("Loading %s...\n", fname.c_str());
+        al::span<const char> res{GetResource(residx)};
+        if(res.empty())
+        {
+            ERR("Could not get resource %u, %s\n", residx, name.c_str());
+            return nullptr;
+        }
+        stream = std::make_unique<idstream>(res.begin(), res.end());
+    }
+    else
+    {
+        TRACE("Loading %s...\n", fname.c_str());
+        auto fstr = std::make_unique<al::ifstream>(fname.c_str(), std::ios::binary);
+        if(!fstr->is_open())
+        {
+            ERR("Could not open %s\n", fname.c_str());
+            return nullptr;
+        }
+        stream = std::move(fstr);
+    }
+
+    std::unique_ptr<HrtfStore> hrtf;
+    char magic[sizeof(magicMarker03)];
+    stream->read(magic, sizeof(magic));
+    if(stream->gcount() < static_cast<std::streamsize>(sizeof(magicMarker03)))
+        ERR("%s data is too short (%zu bytes)\n", name.c_str(), stream->gcount());
+    else if(memcmp(magic, magicMarker03, sizeof(magicMarker03)) == 0)
+    {
+        TRACE("Detected data set format v3\n");
+        hrtf = LoadHrtf03(*stream, name.c_str());
+    }
+    else if(memcmp(magic, magicMarker02, sizeof(magicMarker02)) == 0)
+    {
+        TRACE("Detected data set format v2\n");
+        hrtf = LoadHrtf02(*stream, name.c_str());
+    }
+    else if(memcmp(magic, magicMarker01, sizeof(magicMarker01)) == 0)
+    {
+        TRACE("Detected data set format v1\n");
+        hrtf = LoadHrtf01(*stream, name.c_str());
+    }
+    else if(memcmp(magic, magicMarker00, sizeof(magicMarker00)) == 0)
+    {
+        TRACE("Detected data set format v0\n");
+        hrtf = LoadHrtf00(*stream, name.c_str());
+    }
+    else
+        ERR("Invalid header in %s: \"%.8s\"\n", name.c_str(), magic);
+    stream.reset();
+
+    if(!hrtf)
+    {
+        ERR("Failed to load %s\n", name.c_str());
+        return nullptr;
+    }
+
+    if(hrtf->sampleRate != devrate)
+    {
+        TRACE("Resampling HRTF %s (%uhz -> %uhz)\n", name.c_str(), hrtf->sampleRate, devrate);
+
+        /* Calculate the last elevation's index and get the total IR count. */
+        const size_t lastEv{std::accumulate(hrtf->field, hrtf->field+hrtf->fdCount, size_t{0},
+            [](const size_t curval, const HrtfStore::Field &field) noexcept -> size_t
+            { return curval + field.evCount; }
+        ) - 1};
+        const size_t irCount{size_t{hrtf->elev[lastEv].irOffset} + hrtf->elev[lastEv].azCount};
+
+        /* Resample all the IRs. */
+        std::array<std::array<double,HrirLength>,2> inout;
+        PPhaseResampler rs;
+        rs.init(hrtf->sampleRate, devrate);
+        for(size_t i{0};i < irCount;++i)
+        {
+            HrirArray &coeffs = const_cast<HrirArray&>(hrtf->coeffs[i]);
+            for(size_t j{0};j < 2;++j)
+            {
+                std::transform(coeffs.cbegin(), coeffs.cend(), inout[0].begin(),
+                    [j](const float2 &in) noexcept -> double { return in[j]; });
+                rs.process(HrirLength, inout[0].data(), HrirLength, inout[1].data());
+                for(size_t k{0};k < HrirLength;++k)
+                    coeffs[k][j] = static_cast<float>(inout[1][k]);
+            }
+        }
+        rs = {};
+
+        /* Scale the delays for the new sample rate. */
+        float max_delay{0.0f};
+        auto new_delays = al::vector<float2>(irCount);
+        const float rate_scale{static_cast<float>(devrate)/static_cast<float>(hrtf->sampleRate)};
+        for(size_t i{0};i < irCount;++i)
+        {
+            for(size_t j{0};j < 2;++j)
+            {
+                const float new_delay{std::round(hrtf->delays[i][j] * rate_scale) /
+                    float{HrirDelayFracOne}};
+                max_delay = maxf(max_delay, new_delay);
+                new_delays[i][j] = new_delay;
+            }
+        }
+
+        /* If the new delays exceed the max, scale it down to fit (essentially
+         * shrinking the head radius; not ideal but better than a per-delay
+         * clamp).
+         */
+        float delay_scale{HrirDelayFracOne};
+        if(max_delay > MaxHrirDelay)
+        {
+            WARN("Resampled delay exceeds max (%.2f > %d)\n", max_delay, MaxHrirDelay);
+            delay_scale *= float{MaxHrirDelay} / max_delay;
+        }
+
+        for(size_t i{0};i < irCount;++i)
+        {
+            ubyte2 &delays = const_cast<ubyte2&>(hrtf->delays[i]);
+            for(size_t j{0};j < 2;++j)
+                delays[j] = static_cast<ubyte>(float2int(new_delays[i][j]*delay_scale + 0.5f));
+        }
+
+        /* Scale the IR size for the new sample rate and update the stored
+         * sample rate.
+         */
+        const float newIrSize{std::round(static_cast<float>(hrtf->irSize) * rate_scale)};
+        hrtf->irSize = static_cast<uint>(minf(HrirLength, newIrSize));
+        hrtf->sampleRate = devrate;
+    }
+
+    TRACE("Loaded HRTF %s for sample rate %uhz, %u-sample filter\n", name.c_str(),
+        hrtf->sampleRate, hrtf->irSize);
+    handle = LoadedHrtfs.emplace(handle, LoadedHrtf{fname, std::move(hrtf)});
+
+    return HrtfStorePtr{handle->mEntry.get()};
+}
+
+
+void HrtfStore::add_ref()
+{
+    auto ref = IncrementRef(mRef);
+    TRACE("HrtfStore %p increasing refcount to %u\n", decltype(std::declval<void*>()){this}, ref);
+}
+
+void HrtfStore::release()
+{
+    auto ref = DecrementRef(mRef);
+    TRACE("HrtfStore %p decreasing refcount to %u\n", decltype(std::declval<void*>()){this}, ref);
+    if(ref == 0)
+    {
+        std::lock_guard<std::mutex> _{LoadedHrtfLock};
+
+        /* Go through and remove all unused HRTFs. */
+        auto remove_unused = [](LoadedHrtf &hrtf) -> bool
+        {
+            HrtfStore *entry{hrtf.mEntry.get()};
+            if(entry && ReadRef(entry->mRef) == 0)
+            {
+                TRACE("Unloading unused HRTF %s\n", hrtf.mFilename.data());
+                hrtf.mEntry = nullptr;
+                return true;
+            }
+            return false;
+        };
+        auto iter = std::remove_if(LoadedHrtfs.begin(), LoadedHrtfs.end(), remove_unused);
+        LoadedHrtfs.erase(iter, LoadedHrtfs.end());
+    }
+}