# sdl2-compat: audio: Improvements to U16 audio format support.

**URL:** <https://discourse.libsdl.org/t/sdl2-compat-audio-improvements-to-u16-audio-format-support/42857>\
**Category:** SDL Commits\
**Created:** [March 1, 2023, 3:40pm UTC](https://discourse.libsdl.org/t/sdl2-compat-audio-improvements-to-u16-audio-format-support/42857 "2023-03-01T15:40:09Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![SDLPushPostBot](https://discourse.libsdl.org/user_avatar/discourse.libsdl.org/sdlpushpostbot/32/4370_2.png) [@SDLPushPostBot](https://discourse.libsdl.org/u/SDLPushPostBot)\
**Post date:** [March 1, 2023, 3:40pm UTC](https://discourse.libsdl.org/t/sdl2-compat-audio-improvements-to-u16-audio-format-support/42857/1 "2023-03-01T15:40:09Z")

</div>

> <https://github.com/libsdl-org/sdl2-compat/commit/0ca4640f10fbca916b10b68fab680af6c48e87c5>

```diff
From 0ca4640f10fbca916b10b68fab680af6c48e87c5 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Wed, 1 Mar 2023 10:38:07 -0500
Subject: [PATCH] audio: Improvements to U16 audio format support.

---
 src/sdl2_compat.c | 53 ++++++++++++++---------------------------------
 1 file changed, 16 insertions(+), 37 deletions(-)

diff --git a/src/sdl2_compat.c b/src/sdl2_compat.c
index a6abb05..afd4eae 100644
--- a/src/sdl2_compat.c
+++ b/src/sdl2_compat.c
@@ -3279,59 +3279,40 @@ SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained)
     return -1;
 }
 
-/* this converts the buffer in-place. The buffer size does not change. */
-static Sint16 *AudioUi16LSBToSi16Sys(Uint16 *buffer, const size_t num_samples)
+/* `src` and `dst` can be the same pointer. The buffer size does not change. */
+static void AudioUi16LSBToSi16Sys(Sint16 *dst, const Uint16 *src, const size_t num_samples)
 {
     size_t i;
- const Uint16 *src = buffer;
- Sint16 *dst = (Sint16 *) buffer;
-
     for (i = 0; i < num_samples; i++) {
         dst[i] = (Sint16) (SDL_SwapLE16(src[i]) ^ 0x8000);
     }
-
- return dst;
 }
 
-/* this converts the buffer in-place. The buffer size does not change. */
-static Sint16 *AudioUi16MSBToSi16Sys(Uint16 *buffer, const size_t num_samples)
+/* `src` and `dst` can be the same pointer. The buffer size does not change. */
+static void AudioUi16MSBToSi16Sys(Sint16 *dst, const Uint16 *src, const size_t num_samples)
 {
     size_t i;
- const Uint16 *src = buffer;
- Sint16 *dst = (Sint16 *) buffer;
-
     for (i = 0; i < num_samples; i++) {
         dst[i] = (Sint16) (SDL_SwapBE16(src[i]) ^ 0x8000);
     }
-
- return dst;
 }
 
-/* this converts the buffer in-place. The buffer size does not change. */
-static Uint16 *AudioSi16SysToUi16LSB(Sint16 *buffer, const size_t num_samples)
+/* `src` and `dst` can be the same pointer. The buffer size does not change. */
+static void AudioSi16SysToUi16LSB(Uint16 *dst, const Sint16 *src, const size_t num_samples)
 {
     size_t i;
- const Sint16 *src = buffer;
- Uint16 *dst = (Uint16 *) buffer;
-
     for (i = 0; i < num_samples; i++) {
         dst[i] = SDL_SwapLE16(((Uint16) src[i]) ^ 0x8000);
     }
-
- return dst;
 }
-/* this converts the buffer in-place. The buffer size does not change. */
-static Uint16 *AudioSi16SysToUi16MSB(Sint16 *buffer, const size_t num_samples)
+
+/* `src` and `dst` can be the same pointer. The buffer size does not change. */
+static void AudioSi16SysToUi16MSB(Uint16 *dst, const Sint16 *src, const size_t num_samples)
 {
     size_t i;
- const Sint16 *src = buffer;
- Uint16 *dst = (Uint16 *) buffer;
-
     for (i = 0; i < num_samples; i++) {
         dst[i] = SDL_SwapBE16(((Uint16) src[i]) ^ 0x8000);
     }
-
- return dst;
 }
 
 DECLSPEC SDL2_AudioStream * SDLCALL
@@ -3376,11 +3357,10 @@ SDL_AudioStreamPut(SDL2_AudioStream *stream2, const void *buf, int len)
         if (!tmpbuf) {
             return SDL3_OutOfMemory();
         }
- SDL_memcpy(tmpbuf, buf, len);
         if (stream2->src_format == SDL2_AUDIO_U16LSB) {
- AudioUi16LSBToSi16Sys((Uint16 *) tmpbuf, tmpsamples);
+ AudioUi16LSBToSi16Sys(tmpbuf, (const Uint16 *) buf, tmpsamples);
         } else if (stream2->src_format == SDL2_AUDIO_U16MSB) {
- AudioUi16MSBToSi16Sys((Uint16 *) tmpbuf, tmpsamples);
+ AudioUi16MSBToSi16Sys(tmpbuf, (const Uint16 *) buf, tmpsamples);
         }
         retval = SDL3_PutAudioStreamData(stream2->stream3, tmpbuf, len);
         SDL_free(tmpbuf);
@@ -3403,9 +3383,9 @@ SDL_AudioStreamGet(SDL2_AudioStream *stream2, void *buf, int len)
         SDL_assert(len > 0);
         if ((stream2->dst_format == SDL2_AUDIO_U16LSB) || (stream2->dst_format == SDL2_AUDIO_U16MSB)) {
             if (stream2->dst_format == SDL2_AUDIO_U16LSB) {
- AudioSi16SysToUi16LSB((Sint16 *) buf, retval / sizeof (Sint16));
+ AudioSi16SysToUi16LSB((Uint16 *) buf, (const Sint16 *) buf, retval / sizeof (Sint16));
             } else if (stream2->dst_format == SDL2_AUDIO_U16MSB) {
- AudioSi16SysToUi16MSB((Sint16 *) buf, retval / sizeof (Sint16));
+ AudioSi16SysToUi16MSB((Uint16 *) buf, (const Sint16 *) buf, retval / sizeof (Sint16));
             }
         }
     }
@@ -3448,13 +3428,12 @@ SDL_MixAudioFormat(Uint8 *dst, const Uint8 *src, SDL_AudioFormat format, Uint32
         const Uint32 tmpsamples = len / sizeof (Uint16);
         Sint16 *tmpbuf = (Sint16 *) SDL3_malloc(len);
         if (tmpbuf) { /* if malloc fails, oh well, no mixed audio for you. */
- SDL_memcpy(tmpbuf, src, len);
             if (format == SDL2_AUDIO_U16LSB) {
- AudioUi16LSBToSi16Sys((Uint16 *) tmpbuf, tmpsamples);
+ AudioUi16LSBToSi16Sys(tmpbuf, (const Uint16 *) src, tmpsamples);
             } else if (format == SDL2_AUDIO_U16MSB) {
- AudioUi16MSBToSi16Sys((Uint16 *) tmpbuf, tmpsamples);
+ AudioUi16MSBToSi16Sys(tmpbuf, (const Uint16 *) src, tmpsamples);
             }
- SDL3_MixAudioFormat(dst, src, AUDIO_S16SYS, tmpsamples * sizeof (Sint16), volume);
+ SDL3_MixAudioFormat(dst, (const Uint8 *) tmpbuf, AUDIO_S16SYS, tmpsamples * sizeof (Sint16), volume);
             SDL3_free(tmpbuf);
         }
     } else {

```