From f46b6cf6b8733bc3111754d3603a01a7e32c980b Mon Sep 17 00:00:00 2001
From: Nathan Caldwell <saintdev@gmail.com>
Date: Sun, 16 Aug 2009 20:53:32 -0600
Subject: [PATCH] Remove float calculation to scale probabilities.

---
 libavcodec/lagarith.c | 61 ++++++++++++++++++++++++++-------------------------
 1 file changed, 31 insertions(+), 30 deletions(-)

diff --git a/libavcodec/lagarith.c b/libavcodec/lagarith.c
index 61f20430c2..dcb442d8ef 100644
--- a/libavcodec/lagarith.c
+++ b/libavcodec/lagarith.c
@@ -125,7 +125,7 @@ static int lag_read_prob_header(lag_rac *rac, GetBitContext *gb)
 {
     int i, j;
     int prob = 0;
-    double scale_factor = 0;
+    int scale_factor = 0;
     unsigned cumul_prob = 0;
     unsigned cumulative_target = 1;
     unsigned scaled_cumul_prob = 0;
@@ -145,42 +145,43 @@ static int lag_read_prob_header(lag_rac *rac, GetBitContext *gb)
     }
 
     /* Scale probabilities so cumulative probability is an even power of 2. */
-    cumulative_target = 2 << av_log2(cumul_prob-1);
+    scale_factor = cumul_prob ? av_log2(cumul_prob - 1) + 1 : 0;
+    if (cumul_prob & (cumul_prob - 1)) {
+        for (i = 1; i < 257; i++) {
+            rac->prob[i] = ((uint64_t)rac->prob[i] << scale_factor) / cumul_prob;
+            scaled_cumul_prob += rac->prob[i];
+        }
 
-    scale_factor = cumulative_target / (double) cumul_prob;
+        cumulative_target = 1 << scale_factor;
 
-    for (i = 1; i < 257; i++) {
-        rac->prob[i] = (unsigned) (rac->prob[i] * scale_factor);
-        scaled_cumul_prob += rac->prob[i];
-    }
-
-    scaled_cumul_prob = cumulative_target - scaled_cumul_prob;
+        if (scaled_cumul_prob > cumulative_target) {
+            av_log(rac->avctx, AV_LOG_ERROR,
+                   "Scaled probabilities are larger than target!");
+            return -1;
+        }
 
-    if (scaled_cumul_prob > INT_MAX) {
-        av_log(rac->avctx, AV_LOG_ERROR,
-               "Scaled cumulative probability is larger than target!");
-        return -1;
-    }
+        scaled_cumul_prob = cumulative_target - scaled_cumul_prob;
 
-    for (i = 1; scaled_cumul_prob; i = (i & 0x7f) + 1) {
-        if (rac->prob[i]) {
-            rac->prob[i]++;
-            scaled_cumul_prob--;
+        for (i = 1; scaled_cumul_prob; i = (i & 0x7f) + 1) {
+            if (rac->prob[i]) {
+                rac->prob[i]++;
+                scaled_cumul_prob--;
+            }
+            /* Comment from reference source:
+             * if (b & 0x80 == 0) {     // order of operations is 'wrong'; it has been left this way
+             *                          // since the compression change is negligable and fixing it
+             *                          // breaks backwards compatibilty
+             *      b =- (signed int)b;
+             *      b &= 0xFF;
+             * } else {
+             *      b++;
+             *      b &= 0x7f;
+             * }
+             */
         }
-        /* Comment from reference source:
-         * if (b & 0x80 == 0) {     // order of operations is 'wrong'; it has been left this way
-         *                          // since the compression change is negligable and fixing it
-         *                          // breaks backwards compatibilty
-         *      b =- (signed int)b;
-         *      b &= 0xFF;
-         * } else {
-         *      b++;
-         *      b &= 0x7f;
-         * }
-         */
     }
 
-    rac->scale = cumulative_target ? av_log2(cumulative_target) : 0;
+    rac->scale = scale_factor;
 
     /* Fill probability array with cumulative probability for each symbol. */
     for (i = 1; i < 257; i++)
-- 
2.11.4.GIT