commit e80490d431d940f1e549c3a0426a5815d0be4dbf
Author:     Simon Howard <fraggle@gmail.com>
AuthorDate: Sun May 17 13:54:19 2009 +0000
Commit:     Simon Howard <fraggle@gmail.com>
CommitDate: Sun May 17 13:54:19 2009 +0000

    Always use an SDL buffer size that is a power of two. Reduce buffer size
    to 70ms.

    Subversion-branch: /trunk/chocolate-doom
    Subversion-revision: 1524
---
 pcsound/pcsound_sdl.c | 31 +++++++++++++++++++++++++++++--
 src/i_sdlsound.c      | 35 +++++++++++++++++++++++++++++------
 2 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/pcsound/pcsound_sdl.c b/pcsound/pcsound_sdl.c
index 546e6a36..6ba06785 100644
--- a/pcsound/pcsound_sdl.c
+++ b/pcsound/pcsound_sdl.c
@@ -32,7 +32,7 @@
 #include "pcsound.h"
 #include "pcsound_internal.h"

-#define SOUND_SLICE_TIME 100 /* ms */
+#define MAX_SOUND_SLICE_TIME 70 /* ms */
 #define SQUARE_WAVE_AMP 0x2000

 // If true, we initialised SDL and have the responsibility to shut it
@@ -164,6 +164,33 @@ static void PCSound_SDL_Shutdown(void)
     }
 }

+// Calculate slice size, based on MAX_SOUND_SLICE_TIME.
+// The result must be a power of two.
+
+static int GetSliceSize(void)
+{
+    int limit;
+    int n;
+
+    limit = (pcsound_sample_rate * MAX_SOUND_SLICE_TIME) / 1000;
+
+    // Try all powers of two, not exceeding the limit.
+
+    for (n=0;; ++n)
+    {
+        // 2^n <= limit < 2^n+1 ?
+
+        if ((1 << (n + 1)) > limit)
+        {
+            return (1 << n);
+        }
+    }
+
+    // Should never happen?
+
+    return 1024;
+}
+
 static int PCSound_SDL_Init(pcsound_callback_func callback_func)
 {
     int slicesize;
@@ -179,7 +206,7 @@ static int PCSound_SDL_Init(pcsound_callback_func callback_func)
             return 0;
         }

-        slicesize = (SOUND_SLICE_TIME * pcsound_sample_rate) / 1000;
+        slicesize = GetSliceSize();

         if (Mix_OpenAudio(pcsound_sample_rate, AUDIO_S16SYS, 2, slicesize) < 0)
         {
diff --git a/src/i_sdlsound.c b/src/i_sdlsound.c
index 34adf9de..cdb771e9 100644
--- a/src/i_sdlsound.c
+++ b/src/i_sdlsound.c
@@ -49,7 +49,7 @@
 #include "doomdef.h"

 #define LOW_PASS_FILTER
-#define SOUND_SLICE_TIME 100 /* ms */
+#define MAX_SOUND_SLICE_TIME 70 /* ms */
 #define NUM_CHANNELS 16

 static boolean sound_initialised = false;
@@ -65,7 +65,6 @@ int use_libsamplerate = 0;

 extern int mb_used;

-
 // When a sound stops, check if it is still playing.  If it is not,
 // we can mark the sound data as CACHE to be freed back for other
 // means.
@@ -667,10 +666,36 @@ static void I_SDL_ShutdownSound(void)
     sound_initialised = false;
 }

+// Calculate slice size, based on MAX_SOUND_SLICE_TIME.
+// The result must be a power of two.
+
+static int GetSliceSize(void)
+{
+    int limit;
+    int n;
+
+    limit = (snd_samplerate * MAX_SOUND_SLICE_TIME) / 1000;
+
+    // Try all powers of two, not exceeding the limit.
+
+    for (n=0;; ++n)
+    {
+        // 2^n <= limit < 2^n+1 ?
+
+        if ((1 << (n + 1)) > limit)
+        {
+            return (1 << n);
+        }
+    }
+
+    // Should never happen?
+
+    return 1024;
+}
+
 static boolean I_SDL_InitSound(void)
 {
     int i;
-    int slicesize;

     // No sounds yet

@@ -690,9 +715,7 @@ static boolean I_SDL_InitSound(void)
         return false;
     }

-    slicesize = (snd_samplerate * SOUND_SLICE_TIME) / 1000;
-
-    if (Mix_OpenAudio(snd_samplerate, AUDIO_S16SYS, 2, slicesize) < 0)
+    if (Mix_OpenAudio(snd_samplerate, AUDIO_S16SYS, 2, GetSliceSize()) < 0)
     {
         fprintf(stderr, "Error initialising SDL_mixer: %s\n", Mix_GetError());
         return false;