From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 10 Sep 2012 22:16:11 +0000 (-0400)
Subject: reenable word-at-at-time copying in memmove
X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=commitdiff_plain;h=1701e4f3d46b14c4c4be8a46e64f8eaf15a5c061;hp=3b5e69052a867e9d99cf4c655d775bd06e3437f1

reenable word-at-at-time copying in memmove

before restrict was added, memove called memcpy for forward copies and
used a byte-at-a-time loop for reverse copies. this was changed to
avoid invoking UB now that memcpy has an undefined copying order,
making memmove considerably slower.

performance is still rather bad, so I'll be adding asm soon.
---

diff --git a/src/string/memmove.c b/src/string/memmove.c
index 9153a644..27f670e1 100644
--- a/src/string/memmove.c
+++ b/src/string/memmove.c
@@ -1,13 +1,36 @@
 #include <string.h>
+#include <stdint.h>
+
+#define WT size_t
+#define WS (sizeof(WT))
 
 void *memmove(void *dest, const void *src, size_t n)
 {
 	char *d = dest;
 	const char *s = src;
+
 	if (d==s) return d;
-	if ((size_t)(d-s) < n)
-		while (n--) d[n] = s[n];
-	else
-		while (n--) *d++ = *s++;
+	if (s+n <= d || d+n <= s) return memcpy(d, s, n);
+
+	if (d<s) {
+		if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
+			while ((uintptr_t)d % WS) {
+				if (!n--) return dest;
+				*d++ = *s++;
+			}
+			for (; n>=WS; n-=WS, d+=WS, s+=WS) *(WT *)d = *(WT *)s;
+		}
+		for (; n; n--) *d++ = *s++;
+	} else {
+		if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
+			while ((uintptr_t)(d+n) % WS) {
+				if (!n--) return dest;
+				d[n] = s[n];
+			}
+			while (n>=WS) n-=WS, *(WT *)(d+n) = *(WT *)(s+n);
+		}
+		while (n) n--, d[n] = s[n];
+	}
+
 	return dest;
 }