Merge pull request webmproject#53 from webmproject/psnr

make GetPSNR() be the same on ARM and x86
skal65535 · Mar 21, 2018 · 78148b2 · 78148b2
2 parents 494a85d + dea51ad
commit 78148b2
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/src/dichotomy.cc b/src/dichotomy.cc
@@ -261,8 +261,11 @@ float Encoder::ComputeSize(const DCTCoeffs* coeffs) {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-static double GetPSNR(uint64_t err, uint64_t size) {
-  return (err > 0 && size > 0) ? 10. * log10(255. * 255. * size / err) : 99.;
+static float GetPSNR(uint64_t err, uint64_t size) {
+  // This expression is written such that it gives the same result on ARM
+  // and x86 (for large values of err/size in particular). Don't change it!
+  return (err > 0 && size > 0) ? -4.3429448f * log(size / (err / 255. / 255.))
+                               : 99.f;
 }
 
 float Encoder::ComputePSNR() const {