audio: Implemented SIMD support for audio data type converters.

This currently adds an SSE2 implementation (but it's #ifdef'd out for now,
until it's hooked up to the configure script and such).

src/audio/SDL_audio.c

@@ -843,6 +843,8 @@ SDL_GetAudioDriver(int index)
     return NULL;
 }
 
+extern void SDL_ChooseAudioConverters(void);
+
 int
 SDL_AudioInit(const char *driver_name)
 {
@@ -857,6 +859,8 @@ SDL_AudioInit(const char *driver_name)
     SDL_zero(current_audio);
     SDL_zero(open_devices);
 
+    SDL_ChooseAudioConverters();
+
     /* Select the proper audio driver */
     if (driver_name == NULL) {
         driver_name = SDL_getenv("SDL_AUDIODRIVER");

src/audio/SDL_audio_c.h

@@ -53,16 +53,17 @@ extern SDL_AudioFormat SDL_NextAudioFormat(void);
 /* Function to calculate the size and silence for a SDL_AudioSpec */
 extern void SDL_CalculateAudioSpec(SDL_AudioSpec * spec);
 
-void SDLCALL SDL_Convert_S8_to_F32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_U8_to_F32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_S16_to_F32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_U16_to_F32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_S32_to_F32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_F32_to_S8(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_F32_to_U8(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_F32_to_S16(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_F32_to_U16(SDL_AudioCVT *cvt, SDL_AudioFormat format);
-void SDLCALL SDL_Convert_F32_to_S32(SDL_AudioCVT *cvt, SDL_AudioFormat format);
+/* These pointers get set during init to various SIMD implementations. */
+extern SDL_AudioFilter SDL_Convert_S8_to_F32;
+extern SDL_AudioFilter SDL_Convert_U8_to_F32;
+extern SDL_AudioFilter SDL_Convert_S16_to_F32;
+extern SDL_AudioFilter SDL_Convert_U16_to_F32;
+extern SDL_AudioFilter SDL_Convert_S32_to_F32;
+extern SDL_AudioFilter SDL_Convert_F32_to_S8;
+extern SDL_AudioFilter SDL_Convert_F32_to_U8;
+extern SDL_AudioFilter SDL_Convert_F32_to_S16;
+extern SDL_AudioFilter SDL_Convert_F32_to_U16;
+extern SDL_AudioFilter SDL_Convert_F32_to_S32;
 
 
 /* SDL_AudioStream is a new audio conversion interface. It