commit b13ce13c94fedd4ba9a7a7bce277dc2249966399
author Alex Converse <aconverse@google.com> Mon Feb 06 16:22:40 2017 -0800
committer Alex Converse <aconverse@google.com> Wed Feb 08 17:56:30 2017 +0000
tree acad8b414263df051381433ab9c06e2dea24468f
parent 73ad523642d27ec13c2566e0edcc5ce5792bbbfc

ans: Increase the base state to 1<<17.

ans_multion@2017-01-25T21:00:51.374Z ->
ans_multion_rabs17@2017-01-27T19:25:33.101Z
objective-1-fast
   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0494 | -0.0494 | -0.0494 |  -0.0475 | -0.0484 | -0.0488 | -0.0497

Increasing the state any further seems to yield a compression drop.

Change-Id: Iacfd6af7e2b8a47c41033d61e338c5106bd3679c

aom_dsp/ans.h

diff --git a/aom_dsp/ans.h b/aom_dsp/ans.h
index 5a06d9d..a7a2f0e 100644
--- a/aom_dsp/ans.h
+++ b/aom_dsp/ans.h
@@ -33,9 +33,8 @@
 #define RANS_PROB_BITS 15
 #define RANS_PRECISION (1u << RANS_PROB_BITS)
 
-// L_BASE % PRECISION must be 0. Increasing L_BASE beyond 2**15 will cause uabs
-// to overflow.
-#define L_BASE (RANS_PRECISION)
+// L_BASE is the ANS base state. L_BASE % PRECISION must be 0.
+#define L_BASE (1u << 17)
 #define IO_BASE 256
 // Range I = { L_BASE, L_BASE + 1, ..., L_BASE * IO_BASE - 1 }