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Slight cleanup and commenting of the ADPCM decoder

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svn-id: r29682
This commit is contained in:
Filippos Karapetis 2007-12-01 16:31:10 +00:00
parent a77f6157dc
commit d4831be986
2 changed files with 16 additions and 12 deletions
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17
sound/adpcm.cpp
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@ -265,10 +265,10 @@ int16 ADPCMInputStream::decodeMS(ADPCMChannelStatus *c, byte code) {
predictor = (((c->sample1) * (c->coeff1)) + ((c->sample2) * (c->coeff2))) / 256; predictor = (((c->sample1) * (c->coeff1)) + ((c->sample2) * (c->coeff2))) / 256;
predictor += (signed)((code & 0x08) ? (code - 0x10) : (code)) * c->delta; predictor += (signed)((code & 0x08) ? (code - 0x10) : (code)) * c->delta;
if (predictor < -0x8000) if (predictor < -32768)
predictor = -0x8000; predictor = -32768;
else if (predictor > 0x7fff) else if (predictor > 32767)
predictor = 0x7fff; predictor = 32767;
c->sample2 = c->sample1; c->sample2 = c->sample1;
c->sample1 = predictor; c->sample1 = predictor;
@ -345,13 +345,12 @@ int16 ADPCMInputStream::decodeMSIMA(byte code) {
diff = (code & 0x08) ? -E : E; diff = (code & 0x08) ? -E : E;
samp = _status.last + diff; samp = _status.last + diff;
if (samp < -0x8000) if (samp < -32768)
samp = -0x8000; samp = -32768;
else if (samp > 0x7fff) else if (samp > 32767)
samp = 0x7fff; samp = 32767;
_status.last = samp; _status.last = samp;
_status.stepIndex += stepAdjust(code); _status.stepIndex += stepAdjust(code);
if (_status.stepIndex < 0) if (_status.stepIndex < 0)
_status.stepIndex = 0; _status.stepIndex = 0;

11
sound/adpcm.h
View File

@ -34,10 +34,15 @@ namespace Audio {
class AudioStream; 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 { enum typesADPCM {
kADPCMOki, kADPCMOki, // Dialogic/Oki ADPCM (aka VOX)
kADPCMMSIma, kADPCMMSIma, // Microsoft IMA ADPCM
kADPCMMS kADPCMMS // Microsoft ADPCM
}; };
/** /**