adx: use 12-bit coefficients instead of 14-bit to avoid integer overflow

libavcodec/adx.h

@@ -43,8 +43,8 @@ typedef struct {
     int in_temp;
 } ADXContext;
 
-#define    BASEVOL   0x4000
-#define    SCALE1    0x7298
-#define    SCALE2    0x3350
+#define COEFF_BITS  12
+#define COEFF1      0x1CA6
+#define COEFF2      0x0CD4
 
 #endif /* AVCODEC_ADX_H */

libavcodec/adxdec.c

@@ -59,7 +59,7 @@ static void adx_decode(ADXContext *c, int16_t *out, const uint8_t *in, int ch)
     s2 = prev->s2;
     for (i = 0; i < 32; i++) {
         d  = get_sbits(&gb, 4);
-        s0 = (BASEVOL * d * scale + SCALE1 * s1 - SCALE2 * s2) >> 14;
+        s0 = ((d << COEFF_BITS) * scale + COEFF1 * s1 - COEFF2 * s2) >> COEFF_BITS;
         s2 = s1;
         s1 = av_clip_int16(s0);
         *out = s1;

libavcodec/adxenc.c

@@ -48,7 +48,7 @@ static void adx_encode(unsigned char *adx,const short *wav,
     s2 = prev->s2;
     for(i=0;i<32;i++) {
         s0 = wav[i];
-        d = ((s0<<14) - SCALE1*s1 + SCALE2*s2)/BASEVOL;
+        d = ((s0 << COEFF_BITS) - COEFF1 * s1 + COEFF2 * s2) >> COEFF_BITS;
         data[i]=d;
         if (max<d) max=d;
         if (min>d) min=d;