ref: 7481edb33f5ea82e29f12e0e872d04ea1a5373cb
parent: 240726ac85c16792d2bcf656c20248ea24d4734c
author: James Zern <[email protected]>
date: Tue Sep 27 15:43:03 EDT 2016
vpx_dsp/get_prob: make clip_prob branchless + inline the function directly as there was only one consumer (get_prob()) this is an attempt to reduce the amount of branches to workaround an amd bug. this change is mildly faster or neutral across x86-64, arm. http://support.amd.com/TechDocs/44739_12h_Rev_Gd.pdf 665 Integer Divide Instruction May Cause Unpredictable Behavior BUG=chromium:639712 Suggested-by: Pascal Massimino <[email protected]> Change-Id: Ia91823aded79aab469dd68095d44300e8df04ed2
--- a/vpx_dsp/prob.h
+++ b/vpx_dsp/prob.h
@@ -43,13 +43,14 @@
typedef const vpx_tree_index vpx_tree[];
-static INLINE vpx_prob clip_prob(int p) {- return (p > 255) ? 255 : (p < 1) ? 1 : p;
-}
-
static INLINE vpx_prob get_prob(unsigned int num, unsigned int den) {if (den == 0) return 128u;
- return clip_prob((int)(((int64_t)num * 256 + (den >> 1)) / den));
+ {+ const int p = (int)(((int64_t)num * 256 + (den >> 1)) / den);
+ // (p > 255) ? 255 : (p < 1) ? 1 : p;
+ const int clipped_prob = p | ((255 - p) >> 23) | (p == 0);
+ return (vpx_prob)clipped_prob;
+ }
}
static INLINE vpx_prob get_binary_prob(unsigned int n0, unsigned int n1) {