eden-emu/opus
19
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

fixed-point: log approximation

Browse source
This commit is contained in:
Jean-Marc Valin 2008-02-28 22:14:54 +11:00
parent 98193470ec
commit 2eaba8ac1f
2 changed files with 51 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

18
libcelt/mathops.h
View file

@ -54,6 +54,11 @@
#include "entcode.h"
static inline celt_int16_t celt_ilog2(celt_word32_t x)
{
return EC_ILOG(x)-1;
}
#define C0 3634
#define C1 21173
#define C2 -12627
@ -116,6 +121,19 @@ 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;
/*-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])))))));
/*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);
}
#endif