ref: 96069fd013043d8979fd4d41aac1cedbd05e2e92
parent: 684fb28eba163857fc4bcd5d04f37b9450a8c753
author: Jean-Marc Valin <[email protected]>
date: Tue Apr 15 17:14:18 EDT 2008
optimisation: managed to avoid dividing in the "full gain" case of alg_quant()
--- a/libcelt/vq.c
+++ b/libcelt/vq.c
@@ -183,42 +183,43 @@
best_num = Rxy;
best_id = j;
}
- } while (++j<N); /* Promises we loop at least once */
+ } while (++j<N);
} else {celt_word16_t g;
- celt_word32_t best_num = -VERY_LARGE32;
- for (j=0;j<N;j++)
- {+ celt_word16_t best_num = -VERY_LARGE16;
+ celt_word16_t best_den = 0;
+ j=0;
+ do {celt_word16_t Rxy, Ryy, Ryp;
- celt_word32_t num;
+ celt_word16_t num;
/* Select sign based on X[j] alone */
s = signx[j]*magnitude;
/* 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 */
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 = EXTRACT16(SHR32(MULT16_32_Q15(
- celt_psqrt(MULT16_16(Ryp,Ryp) +
- MULT16_16(Ryy,QCONST16(1.f,14)-Rpp))
- - Ryp,
- celt_rcp(Ryy)),4));
+ /* Compute the gain such that ||p + g*y|| = 1
+ ...but instead, we compute g*Ryy to avoid dividing */
+ g = celt_psqrt(MULT16_16(Ryp,Ryp) + MULT16_16(Ryy,QCONST16(1.f,14)-Rpp)) - Ryp;
/* 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*g*Rxy - g*g*Ryy;*/
#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
- num = 2*g*Rxy - g*g*Ryy;
+ num = g*(2*Rxy-g);
#endif
- if (num >= best_num)
+ if (MULT16_16(best_den, num) > MULT16_16(Ryy, best_num))
{+ best_den = Ryy;
best_num = num;
best_id = j;
- }
- }
+ }
+ } while (++j<N);
}
j = best_id;