diff options
Diffstat (limited to 'Modules')
| -rw-r--r-- | Modules/audioop.c | 111 |
1 files changed, 71 insertions, 40 deletions
diff --git a/Modules/audioop.c b/Modules/audioop.c index 0c75a46..c938eea 100644 --- a/Modules/audioop.c +++ b/Modules/audioop.c @@ -847,7 +847,7 @@ audioop_lin2adpcm(self, args) { signed char *cp; signed char *ncp; - int len, size, val, step, valprev, delta, index, sign; + int len, size, val, step, valpred, delta, index, sign, vpdiff, diff; object *rv, *state, *str; int i, outputbuffer, bufferstep; @@ -869,10 +869,10 @@ audioop_lin2adpcm(self, args) /* Decode state, should have (value, step) */ if ( state == None ) { /* First time, it seems. Set defaults */ - valprev = 0; + valpred = 0; step = 7; index = 0; - } else if ( !getargs(state, "(iii)", &valprev, &step, &index) ) + } else if ( !getargs(state, "(iii)", &valpred, &step, &index) ) return 0; bufferstep = 1; @@ -883,29 +883,50 @@ audioop_lin2adpcm(self, args) else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 16; /* Step 1 - compute difference with previous value */ - delta = val - valprev; - sign = (delta < 0) ? 8 : 0; - if ( sign ) delta = (-delta); + diff = val - valpred; + sign = (diff < 0) ? 8 : 0; + if ( sign ) diff = (-diff); /* Step 2 - Divide and clamp */ -#ifdef NODIVIDE - Program using shifts and subtracts; -#else - delta = (delta<<2) / step; - if ( delta > 7 ) delta = 7; -#endif - + /* Note: + ** This code *approximately* computes: + ** delta = diff*4/step; + ** vpdiff = (delta+0.5)*step/4; + ** but in shift step bits are dropped. The net result of this is + ** that even if you have fast mul/div hardware you cannot put it to + ** good use since the fixup would be too expensive. + */ + delta = 0; + vpdiff = (step >> 3); + + if ( diff >= step ) { + delta = 4; + diff -= step; + vpdiff += step; + } + step >>= 1; + if ( diff >= step ) { + delta |= 2; + diff -= step; + vpdiff += step; + } + step >>= 1; + if ( diff >= step ) { + delta |= 1; + vpdiff += step; + } + /* Step 3 - Update previous value */ if ( sign ) - valprev -= (delta*step)>>2; + valpred -= vpdiff; else - valprev += (delta*step)>>2; + valpred += vpdiff; /* Step 4 - Clamp previous value to 16 bits */ - if ( valprev > 32767 ) - valprev = 32767; - else if ( valprev < -32768 ) - valprev = -32768; + if ( valpred > 32767 ) + valpred = 32767; + else if ( valpred < -32768 ) + valpred = -32768; /* Step 5 - Assemble value, update index and step values */ delta |= sign; @@ -915,15 +936,15 @@ audioop_lin2adpcm(self, args) if ( index > 88 ) index = 88; step = stepsizeTable[index]; - /* Step 6 - Output value (as a whole byte, currently) */ + /* Step 6 - Output value */ if ( bufferstep ) { - outputbuffer = (delta << 4); + outputbuffer = (delta << 4) & 0xf0; } else { - *ncp++ = delta | outputbuffer; + *ncp++ = (delta & 0x0f) | outputbuffer; } bufferstep = !bufferstep; } - rv = mkvalue("(O(iii))", str, valprev, step, index); + rv = mkvalue("(O(iii))", str, valpred, step, index); DECREF(str); return rv; } @@ -935,7 +956,7 @@ audioop_adpcm2lin(self, args) { signed char *cp; signed char *ncp; - int len, size, val, valprev, step, delta, index, sign; + int len, size, val, valpred, step, delta, index, sign, vpdiff; object *rv, *str, *state; int i, inputbuffer, bufferstep; @@ -951,10 +972,10 @@ audioop_adpcm2lin(self, args) /* Decode state, should have (value, step) */ if ( state == None ) { /* First time, it seems. Set defaults */ - valprev = 0; + valpred = 0; step = 7; index = 0; - } else if ( !getargs(state, "(iii)", &valprev, &step, &index) ) + } else if ( !getargs(state, "(iii)", &valpred, &step, &index) ) return 0; str = newsizedstringobject(NULL, len*size*2); @@ -975,36 +996,46 @@ audioop_adpcm2lin(self, args) bufferstep = !bufferstep; + /* Step 2 - Find new index value (for later) */ index += indexTable[delta]; if ( index < 0 ) index = 0; if ( index > 88 ) index = 88; - /* Step 2 - Separate sign and magnitude */ + /* Step 3 - Separate sign and magnitude */ sign = delta & 8; delta = delta & 7; - /* Step 3 - update output value */ + /* Step 4 - Compute difference and new predicted value */ + /* + ** Computes 'vpdiff = (delta+0.5)*step/4', but see comment + ** in adpcm_coder. + */ + vpdiff = step >> 3; + if ( delta & 4 ) vpdiff += step; + if ( delta & 2 ) vpdiff += step>>1; + if ( delta & 1 ) vpdiff += step>>2; + if ( sign ) - valprev -= (delta*step) >> 2; + valpred -= vpdiff; else - valprev += (delta*step) >> 2; + valpred += vpdiff; - /* Step 4 - clamp output value */ - if ( valprev > 32767 ) - valprev = 32767; - else if ( valprev < -32768 ) - valprev = -32768; + /* Step 5 - clamp output value */ + if ( valpred > 32767 ) + valpred = 32767; + else if ( valpred < -32768 ) + valpred = -32768; - /* Step 5 - Update step value */ + /* Step 6 - Update step value */ step = stepsizeTable[index]; /* Step 6 - Output value */ - if ( size == 1 ) *CHARP(ncp, i) = (signed char)(valprev >> 8); - else if ( size == 2 ) *SHORTP(ncp, i) = (short)(valprev); - else if ( size == 4 ) *LONGP(ncp, i) = (long)(valprev<<16); + if ( size == 1 ) *CHARP(ncp, i) = (signed char)(valpred >> 8); + else if ( size == 2 ) *SHORTP(ncp, i) = (short)(valpred); + else if ( size == 4 ) *LONGP(ncp, i) = (long)(valpred<<16); } - rv = mkvalue("(O(iii))", str, valprev, step, index); + rv = mkvalue("(O(iii))", str, valpred, step, index); DECREF(str); return rv; } |