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-rw-r--r--lib/stdlib/mem.c34
1 files changed, 26 insertions, 8 deletions
diff --git a/lib/stdlib/mem.c b/lib/stdlib/mem.c
index 145d651..f1f335a 100644
--- a/lib/stdlib/mem.c
+++ b/lib/stdlib/mem.c
@@ -63,29 +63,47 @@ int memcmp(const void *s1, const void *s2, size_t len)
return 0;
}
-
/*
- * Move @len bytes from @src to @dst
+ * Copy @len bytes from @src to @dst
*/
-void *memmove(void *dst, const void *src, size_t len)
+void *memcpy(void *dst, const void *src, size_t len)
{
const char *s = src;
char *d = dst;
while (len--)
*d++ = *s++;
- return d;
+
+ return dst;
}
/*
- * Copy @len bytes from @src to @dst
+ * Move @len bytes from @src to @dst
*/
-void *memcpy(void *dst, const void *src, size_t len)
+void *memmove(void *dst, const void *src, size_t len)
{
- return memmove(dst, src, len);
+ /*
+ * The following test makes use of unsigned arithmetic overflow to
+ * more efficiently test the condition !(src <= dst && dst < str+len).
+ * It also avoids the situation where the more explicit test would give
+ * incorrect results were the calculation str+len to overflow (though
+ * that issue is probably moot as such usage is probably undefined
+ * behaviour and a bug anyway.
+ */
+ if ((size_t)dst - (size_t)src >= len) {
+ /* destination not in source data, so can safely use memcpy */
+ return memcpy(dst, src, len);
+ } else {
+ /* copy backwards... */
+ const char *end = dst;
+ const char *s = (const char *)src + len;
+ char *d = (char *)dst + len;
+ while (d != end)
+ *--d = *--s;
+ }
+ return dst;
}
-
/*
* Scan @len bytes of @src for value @c
*/