From 7c645606c4825aae7754275a598bbd129a8c6374 Mon Sep 17 00:00:00 2001
From: Jean-Marc Valin <jmvalin@jmvalin.ca>
Date: Fri, 19 Feb 2016 10:44:09 +0800
Subject: [PATCH] Implement sum_sqr_shift() using two passes with no branch
inside the loops
Slightly slower on x86, about the same speed on ARMv7, should be faster on
DSPs.
---
silk/sum_sqr_shift.c | 51 +++++++++++++++++++++-----------------------
1 file changed, 24 insertions(+), 27 deletions(-)
diff --git a/silk/sum_sqr_shift.c b/silk/sum_sqr_shift.c
index 129df191d..4fd0c3d7d 100644
--- a/silk/sum_sqr_shift.c
+++ b/silk/sum_sqr_shift.c
@@ -41,43 +41,40 @@ void silk_sum_sqr_shift(
)
{
opus_int i, shft;
- opus_int32 nrg_tmp, nrg;
+ opus_uint32 nrg_tmp;
+ opus_int32 nrg;
- nrg = 0;
- shft = 0;
- len--;
- for( i = 0; i < len; i += 2 ) {
- nrg = silk_SMLABB_ovflw( nrg, x[ i ], x[ i ] );
- nrg = silk_SMLABB_ovflw( nrg, x[ i + 1 ], x[ i + 1 ] );
- if( nrg < 0 ) {
- /* Scale down */
- nrg = (opus_int32)silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
- shft = 2;
- i+=2;
- break;
- }
+ /* Do a first run with the maximum shift we could have. */
+ shft = 31-silk_CLZ32(len);
+ /* Let's be conservative with rounding and start with nrg=len. */
+ nrg = len;
+ for( i = 0; i < len - 1; i += 2 ) {
+ nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
+ nrg_tmp = silk_SMLABB_ovflw( nrg_tmp, x[ i + 1 ], x[ i + 1 ] );
+ nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, nrg_tmp, shft );
}
- for( ; i < len; i += 2 ) {
+ if( i < len ) {
+ /* One sample left to process */
+ nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
+ nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, nrg_tmp, shft );
+ }
+ silk_assert( nrg >= 0 );
+ /* Make sure the result will fit in a 32-bit signed integer with two bits
+ of headroom. */
+ shft = silk_max_32(0, shft+3 - silk_CLZ32(nrg));
+ nrg = 0;
+ for( i = 0 ; i < len - 1; i += 2 ) {
nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
nrg_tmp = silk_SMLABB_ovflw( nrg_tmp, x[ i + 1 ], x[ i + 1 ] );
- nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, (opus_uint32)nrg_tmp, shft );
- if( nrg < 0 ) {
- /* Scale down */
- nrg = (opus_int32)silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
- shft += 2;
- }
+ nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, nrg_tmp, shft );
}
- if( i == len ) {
+ if( i < len ) {
/* One sample left to process */
nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, nrg_tmp, shft );
}
- /* Make sure to have at least one extra leading zero (two leading zeros in total) */
- if( nrg & 0xC0000000 ) {
- nrg = silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
- shft += 2;
- }
+ silk_assert( nrg >= 0 );
/* Output arguments */
*shift = shft;
--
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