diff options
Diffstat (limited to 'audio')
| -rw-r--r-- | audio/decoders/adpcm.cpp | 23 | ||||
| -rw-r--r-- | audio/decoders/adpcm_intern.h | 17 |
2 files changed, 28 insertions, 12 deletions
diff --git a/audio/decoders/adpcm.cpp b/audio/decoders/adpcm.cpp index 2391bdcab7..43b5a0b3da 100644 --- a/audio/decoders/adpcm.cpp +++ b/audio/decoders/adpcm.cpp @@ -110,7 +110,7 @@ int16 Oki_ADPCMStream::decodeOKI(byte code) { samp = CLIP<int16>(samp, -2048, 2047); _status.ima_ch[0].last = samp; - _status.ima_ch[0].stepIndex += stepAdjust(code); + _status.ima_ch[0].stepIndex += _stepAdjustTable[code]; _status.ima_ch[0].stepIndex = CLIP<int32>(_status.ima_ch[0].stepIndex, 0, ARRAYSIZE(okiStepSize) - 1); // * 16 effectively converts 12-bit input to 16-bit output @@ -404,14 +404,15 @@ int DK3_ADPCMStream::readBuffer(int16 *buffer, const int numSamples) { #pragma mark - -// adjust the step for use on the next sample. -int16 ADPCMStream::stepAdjust(byte code) { - static const int16 adjusts[] = {-1, -1, -1, -1, 2, 4, 6, 8}; - - return adjusts[code & 0x07]; -} +// This table is used to adjust the step for use on the next sample. +// We could half the table, but since the lookup index used is always +// a 4-bit nibble, it's more efficient to just keep it as it is. +const int16 ADPCMStream::_stepAdjustTable[16] = { + -1, -1, -1, -1, 2, 4, 6, 8, + -1, -1, -1, -1, 2, 4, 6, 8 +}; -static const uint16 imaStepTable[89] = { +const int16 Ima_ADPCMStream::_imaTable[89] = { 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, 50, 55, 60, 66, @@ -427,13 +428,13 @@ static const uint16 imaStepTable[89] = { }; int16 Ima_ADPCMStream::decodeIMA(byte code, int channel) { - int32 E = (2 * (code & 0x7) + 1) * imaStepTable[_status.ima_ch[channel].stepIndex] / 8; + int32 E = (2 * (code & 0x7) + 1) * _imaTable[_status.ima_ch[channel].stepIndex] / 8; int32 diff = (code & 0x08) ? -E : E; int32 samp = CLIP<int32>(_status.ima_ch[channel].last + diff, -32768, 32767); _status.ima_ch[channel].last = samp; - _status.ima_ch[channel].stepIndex += stepAdjust(code); - _status.ima_ch[channel].stepIndex = CLIP<int32>(_status.ima_ch[channel].stepIndex, 0, ARRAYSIZE(imaStepTable) - 1); + _status.ima_ch[channel].stepIndex += _stepAdjustTable[code]; + _status.ima_ch[channel].stepIndex = CLIP<int32>(_status.ima_ch[channel].stepIndex, 0, ARRAYSIZE(_imaTable) - 1); return samp; } diff --git a/audio/decoders/adpcm_intern.h b/audio/decoders/adpcm_intern.h index 8e092e67ad..b566f2c765 100644 --- a/audio/decoders/adpcm_intern.h +++ b/audio/decoders/adpcm_intern.h @@ -61,7 +61,6 @@ protected: } _status; virtual void reset(); - int16 stepAdjust(byte); public: ADPCMStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, uint32 size, int rate, int channels, uint32 blockAlign); @@ -72,6 +71,16 @@ public: virtual int getRate() const { return _rate; } virtual bool rewind(); + + + /** + * This table is used by some ADPCM variants (IMA and OKI) to adjust the + * step for use on the next sample. + * The first 8 entries are identical to the second 8 entries. Hence, we + * could half the table in size. But since the lookup index is always a + * 4-bit nibble, it is more efficient to just keep it as it is. + */ + static const int16 _stepAdjustTable[16]; }; class Oki_ADPCMStream : public ADPCMStream { @@ -96,6 +105,12 @@ public: } virtual int readBuffer(int16 *buffer, const int numSamples); + + + /** + * This table is used by decodeIMA. + */ + static const int16 _imaTable[89]; }; class Apple_ADPCMStream : public Ima_ADPCMStream { |