[Scummvm-cvs-logs] SF.net SVN: scummvm: [29682] scummvm/trunk/sound

[thebluegr at users.sourceforge.net]

Revision: 29682
          http://scummvm.svn.sourceforge.net/scummvm/?rev=29682&view=rev
Author:   thebluegr
Date:     2007-12-01 08:31:10 -0800 (Sat, 01 Dec 2007)

Log Message:
-----------
Slight cleanup and commenting of the ADPCM decoder

Modified Paths:
--------------
    scummvm/trunk/sound/adpcm.cpp
    scummvm/trunk/sound/adpcm.h

Modified: scummvm/trunk/sound/adpcm.cpp
===================================================================
--- scummvm/trunk/sound/adpcm.cpp	2007-12-01 16:18:26 UTC (rev 29681)
+++ scummvm/trunk/sound/adpcm.cpp	2007-12-01 16:31:10 UTC (rev 29682)
@@ -265,10 +265,10 @@
 	predictor = (((c->sample1) * (c->coeff1)) + ((c->sample2) * (c->coeff2))) / 256;
 	predictor += (signed)((code & 0x08) ? (code - 0x10) : (code)) * c->delta;
 
-	if (predictor < -0x8000)
-		predictor = -0x8000;
-	else if (predictor > 0x7fff)
-		predictor = 0x7fff;
+	if (predictor < -32768)
+		predictor = -32768;
+	else if (predictor > 32767)
+		predictor = 32767;
 
 	c->sample2 = c->sample1;
 	c->sample1 = predictor;
@@ -345,13 +345,12 @@
 	diff = (code & 0x08) ? -E : E;
 	samp = _status.last + diff;
 
-	if (samp < -0x8000)
-		samp = -0x8000;
-	else if (samp > 0x7fff)
-		samp = 0x7fff;
+	if (samp < -32768)
+		samp = -32768;
+	else if (samp > 32767)
+		samp = 32767;
 
 	_status.last = samp;
-
 	_status.stepIndex += stepAdjust(code);
 	if (_status.stepIndex < 0)
 		_status.stepIndex = 0;

Modified: scummvm/trunk/sound/adpcm.h
===================================================================
--- scummvm/trunk/sound/adpcm.h	2007-12-01 16:18:26 UTC (rev 29681)
+++ scummvm/trunk/sound/adpcm.h	2007-12-01 16:31:10 UTC (rev 29682)
@@ -34,10 +34,15 @@
 
 class AudioStream;
 
+// There are several types of ADPCM encoding, only some are supported here
+// For all the different encodings, refer to: 
+// http://wiki.multimedia.cx/index.php?title=Category:ADPCM_Audio_Codecs
+// Usually, if the audio stream we're trying to play has the FourCC header
+// string intact, it's easy to discern which encoding is used
 enum typesADPCM {
-	kADPCMOki,
-	kADPCMMSIma,
-	kADPCMMS
+	kADPCMOki,		// Dialogic/Oki ADPCM (aka VOX)
+	kADPCMMSIma,	// Microsoft IMA ADPCM
+	kADPCMMS		// Microsoft ADPCM
 };
 
 /**


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