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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2017-02-14 21:51:02 +0000
committerHerbert Xu <herbert@gondor.apana.org.au>2017-03-09 18:34:17 +0800
commit27c539aeffe2851bf9aeeeba8a58038187a05019 (patch)
tree7b886932aea0c06725a51b0cee0ff02b6cf63a4d /crypto
parentb56f5cbc7e08ec7d31c42fc41e5247677f20b143 (diff)
crypto: algapi - annotate expected branch behavior in crypto_inc()
To prevent unnecessary branching, mark the exit condition of the primary loop as likely(), given that a carry in a 32-bit counter occurs very rarely. On arm64, the resulting code is emitted by GCC as 9a8: cmp w1, #0x3 9ac: add x3, x0, w1, uxtw 9b0: b.ls 9e0 <crypto_inc+0x38> 9b4: ldr w2, [x3,#-4]! 9b8: rev w2, w2 9bc: add w2, w2, #0x1 9c0: rev w4, w2 9c4: str w4, [x3] 9c8: cbz w2, 9d0 <crypto_inc+0x28> 9cc: ret where the two remaining branch conditions (one for size < 4 and one for the carry) are statically predicted as non-taken, resulting in optimal execution in the vast majority of cases. Also, replace the open coded alignment test with IS_ALIGNED(). Cc: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto')
-rw-r--r--crypto/algapi.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/crypto/algapi.c b/crypto/algapi.c
index 6b52e8f0b95f..9eed4ef9c971 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -963,11 +963,11 @@ void crypto_inc(u8 *a, unsigned int size)
u32 c;
if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
- !((unsigned long)b & (__alignof__(*b) - 1)))
+ IS_ALIGNED((unsigned long)b, __alignof__(*b)))
for (; size >= 4; size -= 4) {
c = be32_to_cpu(*--b) + 1;
*b = cpu_to_be32(c);
- if (c)
+ if (likely(c))
return;
}