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fixed-point: copied the exp2 implementation from Speex, using it for dB2Amp()

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This commit is contained in:
Jean-Marc Valin 2008-02-28 23:37:26 +11:00
parent 2eaba8ac1f
commit 68b02b1025
2 changed files with 37 additions and 13 deletions
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33
libcelt/mathops.h
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@ -124,17 +124,44 @@ static inline celt_word16_t celt_cos_norm(celt_word32_t x)
static inline celt_word16_t celt_log2(celt_word32_t x)
{
int i;
celt_word16_t n, frac;
/*-0.41446 0.96093 -0.33981 0.15600 */
const celt_word16_t C[4] = {-6791, 7872, -1392, 319};
if (x==0)
return -32767;
i = celt_ilog2(x);
celt_word16_t n = VSHR32(x,i-15)-32768-16384;
celt_word16_t ret = ADD16(C[0], MULT16_16_Q14(n, ADD16(C[1], MULT16_16_Q14(n, ADD16(C[2], MULT16_16_Q14(n, (C[3])))))));
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])))))));
/*printf ("%d %d %d %d\n", x, n, ret, SHL16(i-13,8)+SHR16(ret,14-8));*/
return SHL16(i-13,8)+SHR16(ret,14-8);
return SHL16(i-13,8)+SHR16(frac,14-8);
}
/*
K0 = 1
K1 = log(2)
K2 = 3-4*log(2)
K3 = 3*log(2) - 2
*/
#define D0 16384
#define D1 11356
#define D2 3726
#define D3 1301
/* Input in Q11 format, output in Q16 */
static inline celt_word32_t celt_exp2(celt_word16_t x)
{
int integer;
celt_word16_t frac;
integer = SHR16(x,11);
if (integer>14)
return 0x7fffffff;
else if (integer < -15)
return 0;
frac = SHL16(x-SHL16(integer,11),3);
frac = ADD16(D0, MULT16_16_Q14(frac, ADD16(D1, MULT16_16_Q14(frac, ADD16(D2 , MULT16_16_Q14(D3,frac))))));
return VSHR32(EXTEND32(frac), -integer-2);
}
#endif