Fixed various bugs in the adpcm routines
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 @@
{
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 @@
/* 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 @@
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 @@
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 @@
{
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 @@
/* 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 @@
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;
}