ref: 8967fcaf845ae956c5f59baebd917a5e3da53e56
parent: 980ca6324f01cdfbf6a456b9abc3eb6a9d497520
author: Ronald S. Bultje <rbultje@google.com>
date: Tue Jul 24 11:46:49 EDT 2012
Add comment for use of shift/mul instead of div. Change-Id: Ia6a0090da2097ca9337f8179a6d7b6a09e12f2e6
--- a/vp8/common/quant_common.c
+++ b/vp8/common/quant_common.c
@@ -109,6 +109,9 @@
else if (QIndex < 0)
QIndex = 0;
+ /* For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
+ * The smallest precision for that is '(x*6349) >> 12' but 16 is a good
+ * word size. */
retval = (ac_qlookup[ QIndex ] * 101581) >> 16;
if (retval < 8)