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Increased accuracy of the reciprocal approximation and made it use

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MULT16_16_Q15() instead of Q14 (should be faster).
This commit is contained in:
Jean-Marc Valin 2008-03-12 21:34:50 +11:00
parent 0ac437b82d
commit 887ad9ff29
1 changed files with 7 additions and 4 deletions
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11
libcelt/mathops.h
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@ -165,7 +165,7 @@ static inline celt_word32_t celt_rcp(celt_word16_t x)
{ {
int i, neg=0; int i, neg=0;
celt_word16_t n, frac; 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) if (x<0)
{ {
neg = 1; neg = 1;
@ -174,9 +174,12 @@ static inline celt_word32_t celt_rcp(celt_word16_t x)
if (x==0) if (x==0)
return 0; return 0;
i = celt_ilog2(x); i = celt_ilog2(x);
n = VSHR32(x,i-15)-32768-16384; n = VSHR32(x,i-16)-SHL32(EXTEND32(3),15);
frac = ADD16(C[0], MULT16_16_Q14(n, ADD16(C[1], MULT16_16_Q14(n, ADD16(C[2], MULT16_16_Q14(n, (C[3]))))))); frac = ADD16(C[0], MULT16_16_Q15(n, ADD16(C[1], MULT16_16_Q15(n, ADD16(C[2],
return neg ? -SHL32(EXTEND32(frac),17-i) : SHL32(EXTEND32(frac),17-i); 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 */ #endif /* FIXED_POINT */