[FFmpeg-devel] [PATCH] avcodec/golomb: simplify sign conversion

[zhaoxiu.zeng]

>From 7d782e106cf485ca9a44d4283a18402bf0a84fb9 Mon Sep 17 00:00:00 2001
From: Zeng Zhaoxiu <zhaoxiu.zeng at gmail.com>
Date: Sat, 14 Feb 2015 00:44:39 +0800
Subject: [PATCH] avcodec/golomb: simplify sign conversion

Signed-off-by: Zeng Zhaoxiu <zhaoxiu.zeng at gmail.com>
---
 libavcodec/golomb.h | 41 +++++++++++++----------------------------
 1 file changed, 13 insertions(+), 28 deletions(-)

diff --git a/libavcodec/golomb.h b/libavcodec/golomb.h
index c4b1354..1632ee3 100644
--- a/libavcodec/golomb.h
+++ b/libavcodec/golomb.h
@@ -195,7 +195,7 @@ static inline int get_se_golomb(GetBitContext *gb)
 
         return ff_se_golomb_vlc_code[buf];
     } else {
-        int log = av_log2(buf);
+        int log = av_log2(buf), sign;
         LAST_SKIP_BITS(re, gb, 31 - log);
         UPDATE_CACHE(re, gb);
         buf = GET_CACHE(re, gb);
@@ -205,10 +205,8 @@ static inline int get_se_golomb(GetBitContext *gb)
         LAST_SKIP_BITS(re, gb, 32 - log);
         CLOSE_READER(re, gb);
 
-        if (buf & 1)
-            buf = -(buf >> 1);
-        else
-            buf = (buf >> 1);
+        sign = -(buf & 1);
+        buf  = ((buf >> 1) ^ sign) - sign;
 
         return buf;
     }
@@ -217,13 +215,10 @@ static inline int get_se_golomb(GetBitContext *gb)
 static inline int get_se_golomb_long(GetBitContext *gb)
 {
     unsigned int buf = get_ue_golomb_long(gb);
+    int sign;
 
-    if (buf & 1)
-        buf = (buf + 1) >> 1;
-    else
-        buf = -(buf >> 1);
-
-    return buf;
+    sign = (buf & 1) - 1;
+    return ((buf >> 1) ^ sign) + 1;
 }
 
 static inline int svq3_get_se_golomb(GetBitContext *gb)
@@ -264,13 +259,9 @@ static inline int dirac_get_se_golomb(GetBitContext *gb)
     uint32_t ret = svq3_get_ue_golomb(gb);
 
     if (ret) {
-        uint32_t buf;
-        OPEN_READER(re, gb);
-        UPDATE_CACHE(re, gb);
-        buf = SHOW_SBITS(re, gb, 1);
-        LAST_SKIP_BITS(re, gb, 1);
-        ret = (ret ^ buf) - buf;
-        CLOSE_READER(re, gb);
+        int sign;
+        sign = -get_bits1(gb);
+        ret = (ret ^ sign) - sign;
     }
 
     return ret;
@@ -372,14 +363,11 @@ static inline int get_sr_golomb(GetBitContext *gb, int k, int limit,
                                 int esc_len)
 {
     int v = get_ur_golomb(gb, k, limit, esc_len);
+    int sign;
 
     v++;
-    if (v & 1)
-        return v >> 1;
-    else
-        return -(v >> 1);
-
-//    return (v>>1) ^ -(v&1);
+    sign = (v & 1) - 1;
+    return ((v >> 1) ^ sign) - sign;
 }
 
 /**
@@ -406,10 +394,7 @@ static inline unsigned int get_ur_golomb_shorten(GetBitContext *gb, int k)
 static inline int get_sr_golomb_shorten(GetBitContext *gb, int k)
 {
     int uvar = get_ur_golomb_jpegls(gb, k + 1, INT_MAX, 0);
-    if (uvar & 1)
-        return ~(uvar >> 1);
-    else
-        return uvar >> 1;
+    return (uvar >> 1) ^ -(uvar & 1);
 }
 
 #ifdef TRACE
-- 
2.1.0