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audio: Make sure SDL_AudioStream's work buffer is 16-byte aligned, fo…

…r SIMD.

Note the giantic FIXME, though!
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icculus committed Jan 24, 2017
1 parent 17dcee2 commit 8f627c1cd89a5f5762ad0a34b86d891c45207fe0
Showing with 23 additions and 11 deletions.
  1. +23 −11 src/audio/SDL_audiocvt.c
@@ -867,7 +867,8 @@ struct SDL_AudioStream
SDL_AudioCVT cvt_before_resampling;
SDL_AudioCVT cvt_after_resampling;
SDL_DataQueue *queue;
Uint8 *work_buffer;
Uint8 *work_buffer; /* always aligned to 16 bytes. */
Uint8 *work_buffer_base; /* maybe unaligned pointer from SDL_realloc(). */
int work_buffer_len;
int src_sample_frame_size;
SDL_AudioFormat src_format;
@@ -1125,18 +1126,21 @@ SDL_NewAudioStream(const SDL_AudioFormat src_format,
}

static Uint8 *
EnsureBufferSize(Uint8 **buf, int *len, const int newlen)
EnsureStreamBufferSize(SDL_AudioStream *stream, const int newlen)
{
if (*len < newlen) {
void *ptr = SDL_realloc(*buf, newlen);
if (stream->work_buffer_len < newlen) {
Uint8 *ptr = (Uint8 *) SDL_realloc(stream->work_buffer_base, newlen + 32);
const size_t offset = ((size_t) ptr) & 15;
if (!ptr) {
SDL_OutOfMemory();
return NULL;
}
*buf = (Uint8 *) ptr;
*len = newlen;
/* Make sure we're aligned to 16 bytes for SIMD code. */
stream->work_buffer = offset ? ptr + (16 - offset) : ptr;
stream->work_buffer_base = ptr;
stream->work_buffer_len = newlen;
}
return *buf;
return stream->work_buffer;
}

int
@@ -1145,6 +1149,14 @@ SDL_AudioStreamPut(SDL_AudioStream *stream, const void *buf, const Uint32 _bufle
int buflen = (int) _buflen;
SDL_bool copied = SDL_FALSE;

/* !!! FIXME: several converters can take advantage of SIMD, but only
!!! FIXME: if the data is aligned to 16 bytes. EnsureStreamBufferSize()
!!! FIXME: guarantees the buffer will align, but the
!!! FIXME: converters will iterate over the data backwards if
!!! FIXME: the output grows, and this means we won't align if buflen
!!! FIXME: isn't a multiple of 16. In these cases, we should chop off
!!! FIXME: a few samples at the end and convert them separately. */

if (!stream) {
return SDL_InvalidParamError("stream");
} else if (!buf) {
@@ -1157,7 +1169,7 @@ SDL_AudioStreamPut(SDL_AudioStream *stream, const void *buf, const Uint32 _bufle

if (stream->cvt_before_resampling.needed) {
const int workbuflen = buflen * stream->cvt_before_resampling.len_mult; /* will be "* 1" if not needed */
Uint8 *workbuf = EnsureBufferSize(&stream->work_buffer, &stream->work_buffer_len, workbuflen);
Uint8 *workbuf = EnsureStreamBufferSize(stream, workbuflen);
if (workbuf == NULL) {
return -1; /* probably out of memory. */
}
@@ -1174,7 +1186,7 @@ SDL_AudioStreamPut(SDL_AudioStream *stream, const void *buf, const Uint32 _bufle

if (stream->dst_rate != stream->src_rate) {
const int workbuflen = buflen * ((int) SDL_ceil(stream->rate_incr));
void *workbuf = EnsureBufferSize(&stream->work_buffer, &stream->work_buffer_len, workbuflen);
Uint8 *workbuf = EnsureStreamBufferSize(stream, workbuflen);
if (workbuf == NULL) {
return -1; /* probably out of memory. */
}
@@ -1188,7 +1200,7 @@ SDL_AudioStreamPut(SDL_AudioStream *stream, const void *buf, const Uint32 _bufle

if (stream->cvt_after_resampling.needed) {
const int workbuflen = buflen * stream->cvt_after_resampling.len_mult; /* will be "* 1" if not needed */
Uint8 *workbuf = EnsureBufferSize(&stream->work_buffer, &stream->work_buffer_len, workbuflen);
Uint8 *workbuf = EnsureStreamBufferSize(stream, workbuflen);
if (workbuf == NULL) {
return -1; /* probably out of memory. */
}
@@ -1256,7 +1268,7 @@ SDL_FreeAudioStream(SDL_AudioStream *stream)
stream->cleanup_resampler_func(stream);
}
SDL_FreeDataQueue(stream->queue);
SDL_free(stream->work_buffer);
SDL_free(stream->work_buffer_base);
SDL_free(stream);
}
}

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