Use gcc/clang builtins for av_sat_(add|sub)_64_c if available.

Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/attributes.h

@@ -34,6 +34,12 @@
 #    define AV_GCC_VERSION_AT_MOST(x,y)  0
 #endif
 
+#ifdef __has_builtin
+#    define AV_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#    define AV_HAS_BUILTIN(x) false
+#endif
+
 #ifndef av_always_inline
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define av_always_inline __attribute__((always_inline)) inline

libavutil/common.h

@@ -299,11 +299,16 @@ static av_always_inline int av_sat_dsub32_c(int a, int b)
  * @return sum with signed saturation
  */
 static av_always_inline int64_t av_sat_add64_c(int64_t a, int64_t b) {
+#if (!defined(__INTEL_COMPILER) && AV_GCC_VERSION_AT_LEAST(5,1)) || AV_HAS_BUILTIN(__builtin_add_overflow)
+    int64_t tmp;
+    return !__builtin_add_overflow(a, b, &tmp) ? tmp : (tmp < 0 ? INT64_MAX : INT64_MIN);
+#else
     if (b >= 0 && a >= INT64_MAX - b)
         return INT64_MAX;
     if (b <= 0 && a <= INT64_MIN - b)
         return INT64_MIN;
     return a + b;
+#endif
 }
 
 /**
@@ -314,11 +319,16 @@ static av_always_inline int64_t av_sat_add64_c(int64_t a, int64_t b) {
  * @return difference with signed saturation
  */
 static av_always_inline int64_t av_sat_sub64_c(int64_t a, int64_t b) {
+#if (!defined(__INTEL_COMPILER) && AV_GCC_VERSION_AT_LEAST(5,1)) || AV_HAS_BUILTIN(__builtin_sub_overflow)
+    int64_t tmp;
+    return !__builtin_sub_overflow(a, b, &tmp) ? tmp : (tmp < 0 ? INT64_MAX : INT64_MIN);
+#else
     if (b <= 0 && a >= INT64_MAX + b)
         return INT64_MAX;
     if (b >= 0 && a <= INT64_MIN + b)
         return INT64_MIN;
     return a - b;
+#endif
 }
 
 /**