Optimization for isZero to reduce processor instructions

Results showed an improvement of ~0.58% of app cpu-cycles that happen
mostly within RenderNodeDrawable::onDraw hits this path every frame during view
drawing traversal. At the assembly code level, the fabsf fuction is
instrinsic and replaced by a single instruction which is the reason this
code is more optimal.

Did further benchmarking with a binary that contained a for loop
iterating on calling this function and the cpu-cycle results obtained are:

Overhead  Shared Object                                   Symbol
16.87%    /data/local/tmp/edgartest                       isZeroOld(float)
9.66%     /data/local/tmp/edgartest                       isZeroNew(float)

where isZeroNew is the proposed function, and we can see it is ~40% faster
than the old method.

Test: Ran hwuimacro benchmarks and also did some benchmarking with my
own binary

Change-Id: I68b7db1bf501a3faa669ad5b7d3807ad9cb8798e

1 files changed, 3 insertions, 1 deletions

diff --git a/libs/hwui/utils/MathUtils.h b/libs/hwui/utils/MathUtils.h
index cc8d83f10d43..62bf39ca8a7a 100644
--- a/libs/hwui/utils/MathUtils.h
+++ b/libs/hwui/utils/MathUtils.h
@@ -31,7 +31,9 @@ public:
      * Check for floats that are close enough to zero.
      */
     inline static bool isZero(float value) {
-        return (value >= -NON_ZERO_EPSILON) && (value <= NON_ZERO_EPSILON);
+        // Using fabsf is more performant as ARM computes
+        // fabsf in a single instruction.
+        return fabsf(value) <= NON_ZERO_EPSILON;
     }
 
     inline static bool isOne(float value) {