Add av_clip_uintp2() function

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/vp8.c

@@ -1329,9 +1329,7 @@ static av_always_inline void filter_level_for_mb(VP8Context *s, VP8Macroblock *m
         filter_level += s->lf_delta.mode[mb->mode];
     }
 
-/* Like av_clip for inputs 0 and max, where max is equal to (2^n-1) */
-#define POW2CLIP(x,max) (((x) & ~max) ? (-(x))>>31 & max : (x));
-    filter_level = POW2CLIP(filter_level, 63);
+    filter_level = av_clip_uintp2(filter_level, 6);
 
     interior_limit = filter_level;
     if (s->filter.sharpness) {

libavutil/common.h

@@ -169,6 +169,18 @@ static av_always_inline av_const int32_t av_clipl_int32_c(int64_t a)
     else                                         return a;
 }
 
+/**
+ * Clip a signed integer to an unsigned power of two range.
+ * @param  a value to clip
+ * @param  p bit position to clip at
+ * @return clipped value
+ */
+static av_always_inline av_const unsigned av_clip_uintp2_c(int a, int p)
+{
+    if (a & ~((1<<p) - 1)) return -a >> 31 & ((1<<p) - 1);
+    else                   return  a;
+}
+
 /**
  * Clip a float value into the amin-amax range.
  * @param a value to clip
@@ -362,6 +374,9 @@ static av_always_inline av_const int av_popcount_c(uint32_t x)
 #ifndef av_clipl_int32
 #   define av_clipl_int32   av_clipl_int32_c
 #endif
+#ifndef av_clip_uintp2
+#   define av_clip_uintp2   av_clip_uintp2_c
+#endif
 #ifndef av_clipf
 #   define av_clipf         av_clipf_c
 #endif