fixed-point: don't truncate 32-bit arg to MULT16_32_Q15

The 32-bit arg and return value have one bit more than required to represent
+/-32767 with 15 fractional bits.

Keeping the most significant bit allows saturation for 16-bit conversion to
sometimes be delayed until after these operations.

Author: karlt

libspeexdsp/fixed_debug.h

@@ -279,7 +279,7 @@ static inline int _MULT16_32_QX(int a, long long b, int Q, char *file, int line)
    {
       fprintf (stderr, "MULT16_32_Q%d: inputs are not short+int: %d %d in %s: line %d\n", Q, (int)a, (int)b, file, line);
    }
-   if (ABS32(b)>=(EXTEND32(1)<<(15+Q)))
+   if (ABS(b)>>(16+Q))
       fprintf (stderr, "MULT16_32_Q%d: second operand too large: %d %d in %s: line %d\n", Q, (int)a, (int)b, file, line);
    res = (((long long)a)*(long long)b) >> Q;
    if (!VERIFY_INT(res))
@@ -295,7 +295,7 @@ static inline int MULT16_32_PX(int a, long long b, int Q)
    {
       fprintf (stderr, "MULT16_32_P%d: inputs are not short+int: %d %d\n", Q, (int)a, (int)b);
    }
-   if (ABS32(b)>=(EXTEND32(1)<<(15+Q)))
+   if (ABS(b)>>(16+Q))
       fprintf (stderr, "MULT16_32_Q%d: second operand too large: %d %d\n", Q, (int)a, (int)b);
    res = ((((long long)a)*(long long)b) + ((EXTEND32(1)<<Q)>>1))>> Q;
    if (!VERIFY_INT(res))

libspeexdsp/fixed_generic.h

@@ -76,9 +76,9 @@
 
 #define MAC16_16(c,a,b) (ADD32((c),MULT16_16((a),(b))))
 
-#define MULT16_32_P15(a,b) ADD32(MULT16_16((a),SHR((b),15)), PSHR(MULT16_16((a),((b)&0x00007fff)),15))
-#define MULT16_32_Q15(a,b) ADD32(MULT16_16((a),SHR((b),15)), SHR(MULT16_16((a),((b)&0x00007fff)),15))
-#define MAC16_32_Q15(c,a,b) ADD32(c,ADD32(MULT16_16((a),SHR((b),15)), SHR(MULT16_16((a),((b)&0x00007fff)),15)))
+#define MULT16_32_P15(a,b) ADD32((a)*SHR((b),15), PSHR(MULT16_16((a),((b)&0x00007fff)),15))
+#define MULT16_32_Q15(a,b) ADD32((a)*SHR((b),15), SHR(MULT16_16((a),((b)&0x00007fff)),15))
+#define MAC16_32_Q15(c,a,b) ADD32(c,ADD32((a)*SHR((b),15), SHR(MULT16_16((a),((b)&0x00007fff)),15)))
 
 
 #define MAC16_16_Q11(c,a,b)     (ADD32((c),SHR(MULT16_16((a),(b)),11)))