Commit 8f627c1cd89a5f5762ad0a34b86d891c45207fe0
2017-01-24T00:51:33
audio: Make sure SDL_AudioStream's work buffer is 16-byte aligned, for SIMD. Note the giantic FIXME, though!
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diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 6a24118..a09c989 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/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);
}
}