The return value of SDL_MostSignificantBitIndex32(0) is defined as -1.

libsdl-org · Aug 7, 2013 · 32fcb5c · 32fcb5c
1 parent a9506a4
commit 32fcb5c
Showing 1 changed file with 13 additions and 6 deletions.
diff --git a/include/SDL_bits.h b/include/SDL_bits.h
@@ -45,26 +45,33 @@ extern "C" {
  *  with 0. This operation can also be stated as "count leading zeroes" and
  *  "log base 2".
  *
- *  \return Index of the most significant bit.
+ *  \return Index of the most significant bit, or -1 if the value is 0.
  */
-SDL_FORCE_INLINE Sint8
+SDL_FORCE_INLINE int
 SDL_MostSignificantBitIndex32(Uint32 x)
 {
 #if defined(__GNUC__) && __GNUC__ >= 4
     /* Count Leading Zeroes builtin in GCC.
      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
-     */
+	 */
+	if (x == 0) {
+		return -1;
+	}
     return 31 - __builtin_clz(x);
 #else
     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
      * <seander@cs.stanford.edu>, released in the public domain.
      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
      */
     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
-    const Uint8  S[] = {1, 2, 4, 8, 16};
+    const int    S[] = {1, 2, 4, 8, 16};
+
+    int msbIndex = 0;
+	int i;
 
-    Uint8 msbIndex = 0;
-    int i;
+	if (x == 0) {
+		return -1;
+	}
 
     for (i = 4; i >= 0; i--)
     {