Add av_clip_int8(), used in the upcoming VP8 decoder.

Originally committed as revision 23713 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/common.h

@@ -122,6 +122,17 @@ static inline av_const uint8_t av_clip_uint8(int a)
     else           return a;
 }
 
+/**
+ * Clips a signed integer value into the -128,127 range.
+ * @param a value to clip
+ * @return clipped value
+ */
+static inline av_const int8_t av_clip_int8(int a)
+{
+    if ((a+0x80) & ~0xFF) return (a>>31) ^ 0x7F;
+    else                  return a;
+}
+
 /**
  * Clips a signed integer value into the 0-65535 range.
  * @param a value to clip