From fa5947229b2ee136a285c8d46b19915b481bde3c Mon Sep 17 00:00:00 2001 From: Roy Marples Date: Fri, 19 Apr 2019 21:47:37 +0100 Subject: [PATCH] Really add consttime_memequal --- compat/consttime_memequal.h | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) create mode 100644 compat/consttime_memequal.h diff --git a/compat/consttime_memequal.h b/compat/consttime_memequal.h new file mode 100644 index 00000000..98306484 --- /dev/null +++ b/compat/consttime_memequal.h @@ -0,0 +1,28 @@ +/* + * Written by Matthias Drochner . + * Public domain. + */ + +#ifndef CONSTTIME_MEMEQUAL_H +#define CONSTTIME_MEMEQUAL_H +inline static int +consttime_memequal(const void *b1, const void *b2, size_t len) +{ + const unsigned char *c1 = b1, *c2 = b2; + unsigned int res = 0; + + while (len--) + res |= *c1++ ^ *c2++; + + /* + * Map 0 to 1 and [1, 256) to 0 using only constant-time + * arithmetic. + * + * This is not simply `!res' because although many CPUs support + * branchless conditional moves and many compilers will take + * advantage of them, certain compilers generate branches on + * certain CPUs for `!res'. + */ + return (1 & ((res - 1) >> 8)); +} +#endif /* CONSTTIME_MEMEQUAL_H */ -- 2.47.2