mpd/src/pcm/Volume.cxx

// SPDX-License-Identifier: GPL-2.0-or-later
// Copyright The Music Player Daemon Project

#include "Volume.hxx"
#include "Silence.hxx"
#include "Traits.hxx"
#include "lib/fmt/AudioFormatFormatter.hxx"
#include "lib/fmt/RuntimeError.hxx"
#include "util/TransformN.hxx"

#include "Dither.cxx" // including the .cxx file to get inlined templates

#include <cassert>
#include <cstdint>

#include <string.h>

/**
 * Apply software volume, converting to a different sample type.
 */
template<SampleFormat SF, SampleFormat DF,
	 class STraits=SampleTraits<SF>,
	 class DTraits=SampleTraits<DF>>
static constexpr typename DTraits::value_type
PcmVolumeConvert(typename STraits::value_type _sample, int volume) noexcept
{
	typename STraits::long_type sample(_sample);
	sample *= volume;

	static_assert(DTraits::BITS > STraits::BITS,
		      "Destination sample must be larger than source sample");

	/* after multiplying with the volume value, the "sample"
	   variable contains this number of precision bits: source
	   bits plus the volume bits */
	constexpr unsigned BITS = STraits::BITS + PCM_VOLUME_BITS;

	/* .. and now we need to scale to the requested destination
	   bits */

	typename DTraits::value_type result;
	if (BITS > DTraits::BITS)
		result = sample >> (BITS - DTraits::BITS);
	else if (BITS < DTraits::BITS)
		result = sample << (DTraits::BITS - BITS);
	else
		result = sample;

	return result;
}

template<SampleFormat F, class Traits=SampleTraits<F>>
static inline typename Traits::value_type
pcm_volume_sample(PcmDither &dither,
		  typename Traits::value_type _sample,
		  int volume) noexcept
{
	typename Traits::long_type sample(_sample);

	return dither.DitherShift<typename Traits::long_type,
				  Traits::BITS + PCM_VOLUME_BITS,
				  Traits::BITS>(sample * volume);
}

template<SampleFormat F, class Traits=SampleTraits<F>>
static void
pcm_volume_change(PcmDither &dither,
		  typename Traits::pointer dest,
		  typename Traits::const_pointer src,
		  size_t n,
		  int volume) noexcept
{
	transform_n(src, n, dest,
		    [&dither, volume](auto x){
			    return pcm_volume_sample<F, Traits>(dither, x,
								volume);
		    });
}

static void
pcm_volume_change_8(PcmDither &dither,
		    int8_t *dest, const int8_t *src, size_t n,
		    int volume) noexcept
{
	pcm_volume_change<SampleFormat::S8>(dither, dest, src, n, volume);
}

static void
pcm_volume_change_16(PcmDither &dither,
		     int16_t *dest, const int16_t *src, size_t n,
		     int volume) noexcept
{
	pcm_volume_change<SampleFormat::S16>(dither, dest, src, n, volume);
}

static void
PcmVolumeChange16to32(int32_t *dest, const int16_t *src, size_t n,
		      int volume) noexcept
{
	transform_n(src, n, dest,
		    [volume](auto x){
			    return PcmVolumeConvert<SampleFormat::S16,
						    SampleFormat::S24_P32>(x,
									   volume);
		    });
}

static void
pcm_volume_change_24(PcmDither &dither,
		     int32_t *dest, const int32_t *src, size_t n,
		     int volume) noexcept
{
	pcm_volume_change<SampleFormat::S24_P32>(dither, dest, src, n,
						 volume);
}

static void
pcm_volume_change_32(PcmDither &dither,
		     int32_t *dest, const int32_t *src, size_t n,
		     int volume) noexcept
{
	pcm_volume_change<SampleFormat::S32>(dither, dest, src, n, volume);
}

static void
pcm_volume_change_float(float *dest, const float *src, size_t n,
			float volume) noexcept
{
	transform_n(src, n, dest,
		    [volume](float x){ return x * volume; });
}

SampleFormat
PcmVolume::Open(SampleFormat _format, bool allow_convert)
{
	assert(format == SampleFormat::UNDEFINED);

	convert = false;

	switch (_format) {
	case SampleFormat::UNDEFINED:
		throw FmtRuntimeError("Software volume for {} is not implemented",
				      _format);

	case SampleFormat::S8:
		break;

	case SampleFormat::S16:
		if (allow_convert) {
			/* convert S16 to S24 to avoid discarding too
			   many bits of precision in this stage */
			format = _format;
			convert = true;
			return SampleFormat::S24_P32;
		}

		break;

	case SampleFormat::S24_P32:
	case SampleFormat::S32:
	case SampleFormat::FLOAT:
		break;

	case SampleFormat::DSD:
		// TODO: implement this; currently, it's a no-op
		break;
	}

	return format = _format;
}

std::span<const std::byte>
PcmVolume::Apply(std::span<const std::byte> src) noexcept
{
	if (volume == PCM_VOLUME_1 && !convert)
		return src;

	size_t dest_size = src.size();
	if (convert) {
		assert(format == SampleFormat::S16);

		/* converting to S24_P32 */
		dest_size *= 2;
	}

	void *data = buffer.Get(dest_size);

	if (volume == 0) {
		/* optimized special case: 0% volume = memset(0) */
		PcmSilence(std::span{(std::byte *)data, dest_size},
			   format);
		return { (const std::byte *)data, dest_size };
	}

	switch (format) {
	case SampleFormat::UNDEFINED:
		assert(false);
		gcc_unreachable();

	case SampleFormat::S8:
		pcm_volume_change_8(dither, (int8_t *)data,
				    (const int8_t *)src.data(),
				    src.size() / sizeof(int8_t),
				    volume);
		break;

	case SampleFormat::S16:
		if (convert)
			PcmVolumeChange16to32((int32_t *)data,
					      (const int16_t *)src.data(),
					      src.size() / sizeof(int16_t),
					      volume);
		else
			pcm_volume_change_16(dither, (int16_t *)data,
					     (const int16_t *)src.data(),
					     src.size() / sizeof(int16_t),
					     volume);
		break;

	case SampleFormat::S24_P32:
		pcm_volume_change_24(dither, (int32_t *)data,
				     (const int32_t *)src.data(),
				     src.size() / sizeof(int32_t),
				     volume);
		break;

	case SampleFormat::S32:
		pcm_volume_change_32(dither, (int32_t *)data,
				     (const int32_t *)src.data(),
				     src.size() / sizeof(int32_t),
				     volume);
		break;

	case SampleFormat::FLOAT:
		pcm_volume_change_float((float *)data,
					(const float *)src.data(),
					src.size() / sizeof(float),
					pcm_volume_to_float(volume));
		break;

	case SampleFormat::DSD:
		// TODO: implement this; currently, it's a no-op
		return src;
	}

	return { (const std::byte *)data, dest_size };
}