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g723.1: simplify and fix multiplication overflow

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In 16-bit arithmetic, x * 0xffffc is simply x * -4 with extra overflows,
(and the constant was probably meant to be 0xfffc).  Combined with the
shift, this simplifies to -x >> 1.  Finally, clearing the low two bits
with a 32-bit mask and switching to a 32-bit type allows more efficient
code on 32-bit machines.

Signed-off-by: Mans Rullgard <mans@mansr.com>
This commit is contained in:
Mans Rullgard
2012-08-10 01:14:32 +01:00
parent e141cf2c57
commit 52aa3015a3
1 changed files with 2 additions and 2 deletions
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4
libavcodec/g723_1.c
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@@ -956,7 +956,7 @@ static void formant_postfilter(G723_1_Context *p, int16_t *lpc, int16_t *buf)
signal_ptr = filter_signal + LPC_ORDER; signal_ptr = filter_signal + LPC_ORDER;
for (i = 0; i < SUBFRAMES; i++) { for (i = 0; i < SUBFRAMES; i++) {
int16_t temp_vector[SUBFRAME_LEN]; int16_t temp_vector[SUBFRAME_LEN];
int16_t temp; int temp;
int auto_corr[2]; int auto_corr[2];
int scale, energy; int scale, energy;
@@ -975,7 +975,7 @@ static void formant_postfilter(G723_1_Context *p, int16_t *lpc, int16_t *buf)
temp = (auto_corr[0] >> 2) / temp; temp = (auto_corr[0] >> 2) / temp;
} }
p->reflection_coef = (3 * p->reflection_coef + temp + 2) >> 2; p->reflection_coef = (3 * p->reflection_coef + temp + 2) >> 2;
temp = (p->reflection_coef * 0xffffc >> 3) & 0xfffc; temp = -p->reflection_coef >> 1 & ~3;
/* Compensation filter */ /* Compensation filter */
for (j = 0; j < SUBFRAME_LEN; j++) { for (j = 0; j < SUBFRAME_LEN; j++) {