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optimisation: changed some for() loops to do-while() to give the compiler

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a hint that there has to be at least one iteration.
This commit is contained in:
Jean-Marc Valin 2008-03-26 21:31:56 +11:00
parent df7ab43087
commit fed97d58b5
3 changed files with 13 additions and 9 deletions
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17
libcelt/vq.c
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@ -157,8 +157,9 @@ void alg_quant(celt_norm_t *X, celt_mask_t *W, int N, int K, const celt_norm_t *
/* Choose between fast and accurate strategy depending on where we are in the search */
if (pulsesLeft>1)
{
for (j=0;j<N;j++)
{
/* OPT: This loop is very CPU-intensive */
j=0;
do {
celt_word32_t num;
celt_word16_t den;
/* Select sign based on X[j] alone */
@ -173,13 +174,14 @@ void alg_quant(celt_norm_t *X, celt_mask_t *W, int N, int K, const celt_norm_t *
den = ROUND16(Ryy,14);
/* The idea is to check for num/den >= best_num/best_den, but that way
we can do it without any division */
/* OPT: Make sure to use a conditional move here */
if (MULT16_32_Q15(best_den, num) > MULT16_32_Q15(den, best_num))
{
best_den = den;
best_num = num;
best_id = j;
}
}
} while (++j<N); /* Promises we loop at least once */
} else {
for (j=0;j<N;j++)
{
@ -275,17 +277,18 @@ void intra_prediction(celt_norm_t *x, celt_mask_t *W, int N, int K, celt_norm_t
celt_word32_t xy=0, yy=0;
celt_word32_t num;
celt_word16_t den;
/* If this doesn't generate a double-MAC on supported architectures,
/* OPT: If this doesn't generate a double-MAC (on supported architectures),
complain to your compilor vendor */
for (j=0;j<N;j++)
{
j=0;
do {
xy = MAC16_16(xy, x[j], Y[i+N-j-1]);
yy = MAC16_16(yy, Y[i+N-j-1], Y[i+N-j-1]);
}
} while (++j<N); /* Promises we loop at least once */
/* Using xy^2/yy as the score but without having to do the division */
num = MULT16_16(ROUND16(xy,14),ROUND16(xy,14));
den = ROUND16(yy,14);
/* If you're really desperate for speed, just use xy as the score */
/* OPT: Make sure to use a conditional move here */
if (MULT16_32_Q15(best_den, num) > MULT16_32_Q15(den, best_num))
{
best_num = num;