shithub: libvpx

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ref: ef665996ae59a43575272449d0120a67457a7856
parent: b3933e2d3ccf0de83441eac9d22a145c20ac6803
author: Yaowu Xu <yaowu@google.com>
date: Wed Jun 22 06:41:52 EDT 2016 

Prevent negative variance

Due to rounding used computation, HDB variance computation may produce
slightly negative values. This commit adds clamping to make sure
output variance values for 10 and 12 to be non-negative.

Change-Id: Id679aa55a4c201958c4c7d28cd8733b9246a71c8


--- a/vpx_dsp/variance.c
+++ b/vpx_dsp/variance.c
@@ -341,8 +341,10 @@
                                              int b_stride, \
                                              uint32_t *sse) { \
   int sum; \
+  int64_t var; \
   highbd_10_variance(a, a_stride, b, b_stride, W, H, sse, &sum); \
-  return *sse - (((int64_t)sum * sum) / (W * H)); \
+  var = (int64_t)(*sse) - (((int64_t)sum * sum) / (W * H)); \
+  return (var >= 0) ? (uint32_t)var : 0; \
 } \
 \
 uint32_t vpx_highbd_12_variance##W##x##H##_c(const uint8_t *a, \
@@ -351,8 +353,10 @@
                                              int b_stride, \
                                              uint32_t *sse) { \
   int sum; \
+  int64_t var; \
   highbd_12_variance(a, a_stride, b, b_stride, W, H, sse, &sum); \
-  return *sse - (((int64_t)sum * sum) / (W * H)); \
+  var = (int64_t)(*sse) - (((int64_t)sum * sum) / (W * H)); \
+  return (var >= 0) ? (uint32_t)var : 0; \
 }
 
 #define HIGHBD_GET_VAR(S) \