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Defined the celt_rcp() reciprocal approximation

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This commit is contained in:
Jean-Marc Valin 2008-03-12 11:28:26 +11:00
parent 3c7ae6c3b9
commit 931db72e75
1 changed files with 20 additions and 3 deletions
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23
libcelt/mathops.h
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@ -44,7 +44,7 @@
#define celt_exp exp #define celt_exp exp
#define celt_cos_norm(x) (cos((.5f*M_PI)*(x))) #define celt_cos_norm(x) (cos((.5f*M_PI)*(x)))
#define celt_atan atan #define celt_atan atan
#define celt_rcp(x) (1.f/(x))
#endif #endif
@ -161,8 +161,25 @@ static inline celt_word32_t celt_exp2(celt_word16_t x)
return VSHR32(EXTEND32(frac), -integer-2); return VSHR32(EXTEND32(frac), -integer-2);
} }
static inline celt_word32_t celt_rcp(celt_word16_t x)
{
int i, neg=0;
celt_word16_t n, frac;
const celt_word16_t C[4] = {10905, -3624, 1362, -470};
if (x<0)
{
neg = 1;
x = NEG16(x);
}
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);
}
#endif #endif /* FIXED_POINT */
#endif #endif /* MATHOPS_H */