diff options
| -rw-r--r-- | lib/stdlib/mem.c | 34 |
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 */ |