From d4b04d3275af9938c92a386fc9178977f293362c Mon Sep 17 00:00:00 2001
From: Jean-Marc Valin <jmvalin@amazon.com>
Date: Fri, 17 Nov 2023 23:10:59 -0500
Subject: [PATCH] Speed up silk_warped_autocorrelation_FLP()
Reducing the dependency chain between tmp1 and tmp2 at the
cost of an extra multiply.
---
silk/float/warped_autocorrelation_FLP.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/silk/float/warped_autocorrelation_FLP.c b/silk/float/warped_autocorrelation_FLP.c
index 09186e73d..116dab923 100644
--- a/silk/float/warped_autocorrelation_FLP.c
+++ b/silk/float/warped_autocorrelation_FLP.c
@@ -54,11 +54,13 @@ void silk_warped_autocorrelation_FLP(
/* Loop over allpass sections */
for( i = 0; i < order; i += 2 ) {
/* Output of allpass section */
- tmp2 = state[ i ] + warping * ( state[ i + 1 ] - tmp1 );
+ /* We voluntarily use two multiples instead of factoring the expression to
+ reduce the length of the dependency chain (tmp1->tmp2->tmp1... ). */
+ tmp2 = state[ i ] + warping * state[ i + 1 ] - warping * tmp1;
state[ i ] = tmp1;
C[ i ] += state[ 0 ] * tmp1;
/* Output of allpass section */
- tmp1 = state[ i + 1 ] + warping * ( state[ i + 2 ] - tmp2 );
+ tmp1 = state[ i + 1 ] + warping * state[ i + 2 ] - warping * tmp2;
state[ i + 1 ] = tmp2;
C[ i + 1 ] += state[ 0 ] * tmp2;
}
--
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