av_rescale with user specified rounding

Originally committed as revision 3481 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -230,6 +230,14 @@ enum Motion_Est_ID {
     ME_X1
 };
 
+enum AVRounding {
+    AV_ROUND_ZERO     = 0, ///< round toward zero
+    AV_ROUND_INF      = 1, ///< round away from zero
+    AV_ROUND_DOWN     = 2, ///< round toward -infinity
+    AV_ROUND_UP       = 3, ///< round toward +infinity
+    AV_ROUND_NEAR_INF = 5, ///< round to nearest and halfway cases away from zero
+};
+
 typedef struct RcOverride{
     int start_frame;
     int end_frame;
@@ -2061,11 +2069,16 @@ char av_get_pict_type_char(int pict_type);
 int av_reduce(int *dst_nom, int *dst_den, int64_t nom, int64_t den, int64_t max);
 
 /**
- * rescale a 64bit integer.
+ * rescale a 64bit integer with rounding to nearest.
  * a simple a*b/c isnt possible as it can overflow
  */
 int64_t av_rescale(int64_t a, int64_t b, int64_t c);
 
+/**
+ * rescale a 64bit integer with specified rounding.
+ * a simple a*b/c isnt possible as it can overflow
+ */
+int64_t av_rescale_rnd(int64_t a, int64_t b, int64_t c, enum AVRounding);
 
 /**
  * Interface for 0.5.0 version

libavcodec/utils.c

@@ -822,25 +822,33 @@ int av_reduce(int *dst_nom, int *dst_den, int64_t nom, int64_t den, int64_t max)
     return den==0;
 }
 
-int64_t av_rescale(int64_t a, int64_t b, int64_t c){
-    AVInteger ai, ci;
+int64_t av_rescale_rnd(int64_t a, int64_t b, int64_t c, enum AVRounding rnd){
+    AVInteger ai;
+    int64_t r=0;
     assert(c > 0);
     assert(b >=0);
+    assert(rnd >=0 && rnd<=5 && rnd!=4);
     
-    if(a<0) return -av_rescale(-a, b, c);
+    if(a<0) return -av_rescale_rnd(-a, b, c, rnd ^ ((rnd>>1)&1)); 
     
+    if(rnd==AV_ROUND_NEAR_INF) r= c/2;
+    else if(rnd&1)             r= c-1;
+
     if(b<=INT_MAX && c<=INT_MAX){
         if(a<=INT_MAX)
-            return (a * b + c/2)/c;
+            return (a * b + r)/c;
         else
-            return a/c*b + (a%c*b + c/2)/c;
+            return a/c*b + (a%c*b + r)/c;
     }
     
     ai= av_mul_i(av_int2i(a), av_int2i(b));
-    ci= av_int2i(c);
-    ai= av_add_i(ai, av_shr_i(ci,1));
+    ai= av_add_i(ai, av_int2i(r));
     
-    return av_i2int(av_div_i(ai, ci));
+    return av_i2int(av_div_i(ai, av_int2i(c)));
+}
+
+int64_t av_rescale(int64_t a, int64_t b, int64_t c){
+    return av_rescale_rnd(a, b, c, AV_ROUND_NEAR_INF);
 }
 
 /* av_log API */