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Replace ->driver_data with GetAllocatedSoundBySfxinfo

GetAllocatedSoundBySfxinfo is a linked-list look-up on the
list of allocated sounds, rather than the direct-access of the
driver_data pointer.

Previously we used the ->driver_data field of sfxinfo_t to point at the
corresponding allocated_sound_t, but this assumes a 1:1 mapping which
won't be true with pitch-shifted sounds.

The lookups are still cheap, but I did some instrumenting to see
how many iterations this results in. Note that when I ran these tests
there were a few more calls that I've since eliminated, so this is
slightly worse than current. For Doom 2 v1.9 demos:

        ____demo:___
 iter     1   2    3
    0   296 636 1691
    1   104 205 620
    2   57  134 488
    3   55  90  287
    4   58  56  204
    5   28  48  146
    6   18  33  119
    7   6   44  99
    8   4   33  86
    9   8   57  72
    10  6   30  62
    11  6   18  68
    12  6   22  46
    13  2   18  42
    14  4   18  48
    15  0   6   22
    16  4   12  16
    17  0   12  14
    18  0   8   12
    19  0   12  14
    20  0   16  12
    21  0   10  10
    22  0   2   20
    23  0   10  10
    24  0   2   6
    25  0   2   8
    26  0   0   10
    27  0   0   4
    28  0   0   6
    29  0   0   2
    30  0   0   12
    31  0   0   8
    32  0   0   4
    33  0   0   2
    34  0   0   4
    35  0   0   0
    36  0   0   0
    37  0   0   0

--- a/src/i_sdlsound.c

+++ b/src/i_sdlsound.c

@@ -136,10 +136,6 @@

     AllocatedSoundUnlink(snd);

-    // Unlink from higher-level code.

-

-    snd->sfxinfo->driver_data = NULL;

-

     // Keep track of the amount of allocated sound data:

     allocated_sounds_size -= snd->chunk.alen;

@@ -235,10 +231,6 @@

     snd->sfxinfo = sfxinfo;

     snd->use_count = 0;

-    // driver_data pointer points to the allocated_sound structure.

-

-    sfxinfo->driver_data = snd;

-

     // Keep track of how much memory all these cached sounds are using...

     allocated_sounds_size += len;

@@ -279,6 +271,24 @@

     //printf("-- %s: Use count=%i\n", snd->sfxinfo->name, snd->use_count);

 }

+// Search through the list of allocated sounds and return the one that matches

+// the supplied sfxinfo entry.

+

+static allocated_sound_t * GetAllocatedSoundBySfxInfo(sfxinfo_t *sfxinfo)

+{

+    allocated_sound_t * p = allocated_sounds_head;

+

+    while(p != NULL)

+    {

+        if(p->sfxinfo == sfxinfo)

+        {

+            return p;

+        }

+        p = p->next;

+    }

+    return NULL;

+}

+

 // 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.

@@ -787,8 +797,7 @@

 static boolean LockSound(sfxinfo_t *sfxinfo)

 {

     // If the sound isn't loaded, load it now

-

-    if (sfxinfo->driver_data == NULL)

+    if (GetAllocatedSoundBySfxInfo(sfxinfo) == NULL)

     {

         if (!CacheSFX(sfxinfo))

         {

@@ -796,7 +805,7 @@

         }

     }

-    LockAllocatedSound(sfxinfo->driver_data);

+    LockAllocatedSound(GetAllocatedSoundBySfxInfo(sfxinfo));

     return true;

 }

@@ -879,7 +888,7 @@

         return -1;

     }

-    snd = sfxinfo->driver_data;

+    snd = GetAllocatedSoundBySfxInfo(sfxinfo);

     // play sound