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md5_utils,MD5Transform: don't check for unsigned overflow

this transform is well-defined and relies on unsigned rollover

Change-Id: Ia39f3a65a7a07ac871bf857d2684c9839862c2aa

--- a/md5_utils.c

+++ b/md5_utils.c

@@ -150,12 +150,23 @@

 #define MD5STEP(f,w,x,y,z,in,s) \

   (w += f(x,y,z) + in, w = (w<<s | w>>(32-s)) + x)

+#if defined(__clang__) && defined(__has_attribute)

+#if __has_attribute(no_sanitize)

+#define VPX_NO_UNSIGNED_OVERFLOW_CHECK \

+  __attribute__((no_sanitize("unsigned-integer-overflow")))

+#endif

+#endif

+

+#ifndef VPX_NO_UNSIGNED_OVERFLOW_CHECK

+#define VPX_NO_UNSIGNED_OVERFLOW_CHECK

+#endif

+

 /*

  * The core of the MD5 algorithm, this alters an existing MD5 hash to

  * reflect the addition of 16 longwords of new data.  MD5Update blocks

  * the data and converts bytes into longwords for this routine.

  */

-void

+VPX_NO_UNSIGNED_OVERFLOW_CHECK void

 MD5Transform(UWORD32 buf[4], UWORD32 const in[16]) {

   register UWORD32 a, b, c, d;

@@ -237,5 +248,7 @@

   buf[2] += c;

   buf[3] += d;

 }

+

+#undef VPX_NO_UNSIGNED_OVERFLOW_CHECK

 #endif