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optimisation: simplified the "full gain" case of alg_quant() to remove some

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32-bit muls.
This commit is contained in:
Jean-Marc Valin 2008-04-15 18:04:33 +10:00
parent ed317c94c3
commit d568303134
2 changed files with 34 additions and 14 deletions
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17
libcelt/mathops.h
View file

@ -85,6 +85,7 @@ static inline int find_max32(celt_word32_t *x, int len)
#ifndef FIXED_POINT
#define celt_sqrt(x) ((float)sqrt(x))
#define celt_psqrt(x) ((float)sqrt(x))
#define celt_rsqrt(x) (1.f/celt_sqrt(x))
#define celt_acos acos
#define celt_exp exp
@ -153,6 +154,22 @@ static inline celt_word32_t celt_sqrt(celt_word32_t x)
return rt;
}
/** Sqrt approximation (QX input, QX/2 output) that assumes that the input is
strictly positive */
static inline celt_word32_t celt_psqrt(celt_word32_t x)
{
int k;
celt_word16_t n;
celt_word32_t rt;
const celt_word16_t C[5] = {23174, 11584, -3011, 1570, -557};
k = (celt_ilog2(x)>>1)-7;
x = VSHR32(x, (k<<1));
n = x-32768;
rt = 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])))))))));
rt = VSHR32(rt,7-k);
return rt;
}
#define L1 32767
#define L2 -7651

31
libcelt/vq.c
View file

@ -167,9 +167,9 @@ void alg_quant(celt_norm_t *X, celt_mask_t *W, int N, int K, const celt_norm_t *
/* Select sign based on X[j] alone */
s = signx[j]*magnitude;
/* Temporary sums of the new pulse(s) */
Rxy = SHR32(xy + MULT16_16(s,X[j]),rshift);
Rxy = EXTRACT16(SHR32(xy + MULT16_16(s,X[j]),rshift));
/* We're multiplying y[j] by two so we don't have to do it here */
Ryy = SHR32(yy + MULT16_16(s,y[j]),rshift);
Ryy = EXTRACT16(SHR32(yy + MULT16_16(s,y[j]),rshift));
/* Approximate score: we maximise Rxy/sqrt(Ryy) (we're guaranteed that
Rxy is positive because the sign is pre-computed) */
@ -189,27 +189,30 @@ void alg_quant(celt_norm_t *X, celt_mask_t *W, int N, int K, const celt_norm_t *
celt_word32_t best_num = -VERY_LARGE32;
for (j=0;j<N;j++)
{
celt_word32_t Rxy, Ryy, Ryp;
celt_word16_t Rxy, Ryy, Ryp;
celt_word32_t num;
/* Select sign based on X[j] alone */
s = signx[j]*magnitude;
/* Temporary sums of the new pulse(s) */
Rxy = xy + MULT16_16(s,X[j]);
Rxy = ROUND16(xy + MULT16_16(s,X[j]), 14);
/* We're multiplying y[j] by two so we don't have to do it here */
Ryy = yy + MULT16_16(s,y[j]);
Ryp = yp + MULT16_16(s,P[j]);
Ryy = ROUND16(yy + MULT16_16(s,y[j]), 14);
Ryp = ROUND16(yp + MULT16_16(s,P[j]), 14);
/* Compute the gain such that ||p + g*y|| = 1 */
g = MULT16_32_Q15(
celt_sqrt(MULT16_16(ROUND16(Ryp,14),ROUND16(Ryp,14)) + Ryy -
MULT16_16(ROUND16(Ryy,14),Rpp))
- ROUND16(Ryp,14),
celt_rcp(SHR32(Ryy,12)));
g = SHR32(MULT16_32_Q15(
celt_psqrt(MULT16_16(Ryp,Ryp) +
MULT16_16(Ryy,QCONST16(1.f,14)-Rpp))
- Ryp,
celt_rcp(Ryy)),4);
/* Knowing that gain, what's the error: (x-g*y)^2
(result is negated and we discard x^2 because it's constant) */
/* score = 2.f*g*Rxy - 1.f*g*g*Ryy*NORM_SCALING_1;*/
num = 2*MULT16_32_Q14(ROUND16(Rxy,14),g)
- MULT16_32_Q14(EXTRACT16(MULT16_32_Q14(ROUND16(Ryy,14),g)),g);
/* score = 2*g*Rxy - g*g*Ryy;*/
#ifdef FIXED_POINT
num = MULT16_16(Rxy,g) - SHL32(MULT16_16(MULT16_16_Q15(Ryy,g),g),2);
#else
num = 2*g*Rxy - g*g*Ryy;
#endif
if (num >= best_num)
{
best_num = num;