ref: 887ad9ff2983a89350ffd182c51a957d6bc21121
parent: 0ac437b82d40bc3c319a48d7baf8e248143668a2
author: Jean-Marc Valin <[email protected]>
date: Wed Mar 12 17:34:50 EDT 2008
Increased accuracy of the reciprocal approximation and made it use MULT16_16_Q15() instead of Q14 (should be faster).
--- a/libcelt/mathops.h
+++ b/libcelt/mathops.h
@@ -165,7 +165,7 @@
{int i, neg=0;
celt_word16_t n, frac;
- const celt_word16_t C[4] = {10905, -3624, 1362, -470};+ const celt_word16_t C[5] = {21848, -7251, 2403, -934, 327};if (x<0)
{neg = 1;
@@ -174,9 +174,12 @@
if (x==0)
return 0;
i = celt_ilog2(x);
- n = VSHR32(x,i-15)-32768-16384;
- frac = ADD16(C[0], MULT16_16_Q14(n, ADD16(C[1], MULT16_16_Q14(n, ADD16(C[2], MULT16_16_Q14(n, (C[3])))))));
- return neg ? -SHL32(EXTEND32(frac),17-i) : SHL32(EXTEND32(frac),17-i);
+ n = VSHR32(x,i-16)-SHL32(EXTEND32(3),15);
+ frac = ADD16(C[0], MULT16_16_Q15(n, ADD16(C[1], MULT16_16_Q15(n, ADD16(C[2],
+ MULT16_16_Q15(n, ADD16(C[3], MULT16_16_Q15(n, (C[4])))))))));
+ if (neg)
+ frac = -frac;
+ return SHL32(EXTEND32(frac),16-i);
}
#endif /* FIXED_POINT */