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author | Roy Marples <roy@marples.name> | 2019-04-19 21:47:37 +0100 |
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committer | Roy Marples <roy@marples.name> | 2019-04-19 21:47:37 +0100 |
commit | aee631aadeef4283c8a749c1caf77823304acf5e (patch) | |
tree | 624c956154dc53b415fcb2889ebb0e5434b54ce3 | |
parent | cfde89ab66cb4e5957b1c4b68ad6a9449e2784da (diff) | |
download | dhcpcd-aee631aadeef4283c8a749c1caf77823304acf5e.tar.xz |
Really add consttime_memequal
-rw-r--r-- | compat/consttime_memequal.h | 28 |
1 files changed, 28 insertions, 0 deletions
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 <drochner@NetBSD.org>. + * 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 */ |