From b6a47ff58a7831503c6fb53f0820773594fd12d5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Thu, 23 Oct 2014 13:04:30 +0200
Subject: [PATCH] Change loop order in memxor.
---
ChangeLog | 3 +++
memxor.c | 65 +++++++++++++++++++++++++++++++------------------------
2 files changed, 40 insertions(+), 28 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index f611ea2f..8311fec9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
2014-10-23 Niels Möller <nisse@lysator.liu.se>
+ * memxor.c (memxor_common_alignment, memxor_different_alignment)
+ (memxor): Change loop order, iterate from the end.
+
* examples/nettle-benchmark.c (time_memxor): Allocate buffers as
arrays of unsigned long, for more reliable alignment.
diff --git a/memxor.c b/memxor.c
index 99f46f37..e205aba8 100644
--- a/memxor.c
+++ b/memxor.c
@@ -70,13 +70,14 @@ memxor_common_alignment (word_t *dst, const word_t *src, size_t n)
if (n & 1)
{
- *dst++ ^= *src++;
n--;
+ dst[n] ^= src[n];
}
- for (; n >= 2; dst += 2, src += 2, n -= 2)
+ while (n >= 2)
{
- dst[0] ^= src[0];
- dst[1] ^= src[1];
+ n -= 2;
+ dst[n+1] ^= src[n+1];
+ dst[n] ^= src[n];
}
}
@@ -86,7 +87,6 @@ memxor_common_alignment (word_t *dst, const word_t *src, size_t n)
static void
memxor_different_alignment (word_t *dst, const char *src, size_t n)
{
- size_t i;
int shl, shr;
const word_t *src_word;
unsigned offset = ALIGN_OFFSET (src);
@@ -97,21 +97,23 @@ memxor_different_alignment (word_t *dst, const char *src, size_t n)
src_word = (const word_t *) ((uintptr_t) src & -SIZEOF_LONG);
- /* FIXME: Unroll four times, like memcmp? */
- i = n & 1;
- s0 = src_word[i];
- if (i)
+ if (n & 1)
{
- s1 = src_word[0];
- dst[0] ^= MERGE (s1, shl, s0, shr);
+ n--;
+ s1 = src_word[n];
+ s0 = src_word[n+1]; /* FIXME: Overread */
+ dst[n] ^= MERGE (s1, shl, s0, shr);
}
+ else
+ s1 = src_word[n]; /* FIXME: Overread */
- for (; i < n; i += 2)
+ while (n > 0)
{
- s1 = src_word[i+1];
- dst[i] ^= MERGE(s0, shl, s1, shr);
- s0 = src_word[i+2];
- dst[i+1] ^= MERGE(s1, shl, s0, shr);
+ n -= 2;
+ s0 = src_word[n+1];
+ dst[n+1] ^= MERGE(s0, shl, s1, shr);
+ s1 = src_word[n]; /* FIXME: Overread on last iteration */
+ dst[n] ^= MERGE(s1, shl, s0, shr);
}
}
@@ -128,26 +130,33 @@ memxor(void *dst_in, const void *src_in, size_t n)
if (n >= WORD_T_THRESH)
{
+ unsigned i;
+ unsigned offset;
+ size_t nwords;
/* There are at least some bytes to compare. No need to test
for N == 0 in this alignment loop. */
- while (ALIGN_OFFSET (dst))
+ for (i = ALIGN_OFFSET(dst + n); i > 0; i--)
{
- *dst++ ^= *src++;
n--;
+ dst[n] ^= src[n];
}
- if (ALIGN_OFFSET (src))
- memxor_different_alignment ((word_t *) dst, src, n / sizeof(word_t));
- else
- memxor_common_alignment ((word_t *) dst, (const word_t *) src, n / sizeof(word_t));
+ offset = ALIGN_OFFSET(src + n);
+ nwords = n / sizeof (word_t);
+ n %= sizeof (word_t);
- dst += n & -SIZEOF_LONG;
- src += n & -SIZEOF_LONG;
- n = n & (SIZEOF_LONG - 1);
+ if (offset)
+ memxor_different_alignment ((word_t *) (dst+n), (src+n), nwords);
+ else
+ memxor_common_alignment ((word_t *) (dst+n),
+ (const word_t *) (src+n), nwords);
+ }
+ while (n > 0)
+ {
+ n--;
+ dst[n] ^= src[n];
}
- for (; n > 0; n--)
- *dst++ ^= *src++;
- return dst_in;
+ return dst;
}
--
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