From 8967fcaf845ae956c5f59baebd917a5e3da53e56 Mon Sep 17 00:00:00 2001
From: "Ronald S. Bultje" <rbultje@google.com>
Date: Tue, 24 Jul 2012 15:46:49 -0700
Subject: [PATCH] Add comment for use of shift/mul instead of div.

Change-Id: Ia6a0090da2097ca9337f8179a6d7b6a09e12f2e6
---
 vp8/common/quant_common.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/vp8/common/quant_common.c b/vp8/common/quant_common.c
index a0b212cc4..05f921070 100644
--- a/vp8/common/quant_common.c
+++ b/vp8/common/quant_common.c
@@ -109,6 +109,9 @@ int vp8_ac2quant(int QIndex, int Delta)
     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)