Fixed various bugs in the adpcm routines

diff --git a/Modules/audioop.c b/Modules/audioop.c
index 0c75a46d570f24cc8758d2681a79769b55089d0b..c938eea010bb9157a72c6d16f82c3572666d01e0 100644 (file)
--- 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;
 }