From e80490d431d940f1e549c3a0426a5815d0be4dbf Mon Sep 17 00:00:00 2001
From: Simon Howard
Date: Sun, 17 May 2009 13:54:19 +0000
Subject: 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 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

(limited to 'pcsound')

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)
         {
-- 
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