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optimisation: managed to avoid dividing in the "full gain" case of alg_quant()

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Jean-Marc Valin 2008-04-15 21:14:18 +10:00
parent 684fb28eba
commit 96069fd013
1 changed files with 18 additions and 17 deletions
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33
libcelt/vq.c
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@ -183,42 +183,43 @@ void alg_quant(celt_norm_t *X, celt_mask_t *W, int N, int K, const celt_norm_t *
best_num = Rxy; best_num = Rxy;
best_id = j; best_id = j;
} }
} while (++j<N); /* Promises we loop at least once */ } while (++j<N);
} else { } else {
celt_word16_t g; celt_word16_t g;
celt_word32_t best_num = -VERY_LARGE32; celt_word16_t best_num = -VERY_LARGE16;
for (j=0;j<N;j++) celt_word16_t best_den = 0;
{ j=0;
do {
celt_word16_t Rxy, Ryy, Ryp; celt_word16_t Rxy, Ryy, Ryp;
celt_word32_t num; celt_word16_t num;
/* Select sign based on X[j] alone */ /* Select sign based on X[j] alone */
s = signx[j]*magnitude; s = signx[j]*magnitude;
/* Temporary sums of the new pulse(s) */ /* Temporary sums of the new pulse(s) */
Rxy = ROUND16(xy + MULT16_16(s,X[j]), 14); /* We only shift by 13 so we don't have to multiply by 2 later */
Rxy = ROUND16(xy + MULT16_16(s,X[j]), 13);
/* We're multiplying y[j] by two so we don't have to do it here */ /* We're multiplying y[j] by two so we don't have to do it here */
Ryy = ROUND16(yy + MULT16_16(s,y[j]), 14); Ryy = ROUND16(yy + MULT16_16(s,y[j]), 14);
Ryp = ROUND16(yp + MULT16_16(s,P[j]), 14); Ryp = ROUND16(yp + MULT16_16(s,P[j]), 14);
/* Compute the gain such that ||p + g*y|| = 1 */ /* Compute the gain such that ||p + g*y|| = 1
g = EXTRACT16(SHR32(MULT16_32_Q15( ...but instead, we compute g*Ryy to avoid dividing */
celt_psqrt(MULT16_16(Ryp,Ryp) + g = celt_psqrt(MULT16_16(Ryp,Ryp) + MULT16_16(Ryy,QCONST16(1.f,14)-Rpp)) - 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 /* Knowing that gain, what's the error: (x-g*y)^2
(result is negated and we discard x^2 because it's constant) */ (result is negated and we discard x^2 because it's constant) */
/* score = 2*g*Rxy - g*g*Ryy;*/ /* score = 2*g*Rxy - g*g*Ryy;*/
#ifdef FIXED_POINT #ifdef FIXED_POINT
num = MULT16_16(Rxy,g) - SHL32(MULT16_16(MULT16_16_Q15(Ryy,g),g),2); /* No need to multiply Rxy by 2 because we did it earlier */
num = EXTRACT16(SHR32(MULT16_16(SUB16(Rxy,g),g),15));
#else #else
num = 2*g*Rxy - g*g*Ryy; num = g*(2*Rxy-g);
#endif #endif
if (num >= best_num) if (MULT16_16(best_den, num) > MULT16_16(Ryy, best_num))
{ {
best_den = Ryy;
best_num = num; best_num = num;
best_id = j; best_id = j;
} }
} } while (++j<N);
} }
j = best_id; j = best_id;