fix return value of wmemcmp for extreme wchar_t values

[musl] / src / string / memset.c

diff --git a/src/string/memset.c b/src/string/memset.c
index 20e47c4..5613a14 100644 (file)
--- a/src/string/memset.c
+++ b/src/string/memset.c
@@ -1,21 +1,90 @@
 #include <string.h>
-#include <stdlib.h>
 #include <stdint.h>
-#include <limits.h>
-
-#define SS (sizeof(size_t))
-#define ALIGN (sizeof(size_t)-1)
-#define ONES ((size_t)-1/UCHAR_MAX)
 
 void *memset(void *dest, int c, size_t n)
 {
        unsigned char *s = dest;
-       c = (unsigned char)c;
-       for (; ((uintptr_t)s & ALIGN) && n; n--) *s++ = c;
-       if (n) {
-               size_t *w, k = ONES * c;
-               for (w = (void *)s; n>=SS; n-=SS, w++) *w = k;
-               for (s = (void *)w; n; n--, s++) *s = c;
+       size_t k;
+
+       /* Fill head and tail with minimal branching. Each
+        * conditional ensures that all the subsequently used
+        * offsets are well-defined and in the dest region. */
+
+       if (!n) return dest;
+       s[0] = c;
+       s[n-1] = c;
+       if (n <= 2) return dest;
+       s[1] = c;
+       s[2] = c;
+       s[n-2] = c;
+       s[n-3] = c;
+       if (n <= 6) return dest;
+       s[3] = c;
+       s[n-4] = c;
+       if (n <= 8) return dest;
+
+       /* Advance pointer to align it at a 4-byte boundary,
+        * and truncate n to a multiple of 4. The previous code
+        * already took care of any head/tail that get cut off
+        * by the alignment. */
+
+       k = -(uintptr_t)s & 3;
+       s += k;
+       n -= k;
+       n &= -4;
+
+#ifdef __GNUC__
+       typedef uint32_t __attribute__((__may_alias__)) u32;
+       typedef uint64_t __attribute__((__may_alias__)) u64;
+
+       u32 c32 = ((u32)-1)/255 * (unsigned char)c;
+
+       /* In preparation to copy 32 bytes at a time, aligned on
+        * an 8-byte bounary, fill head/tail up to 28 bytes each.
+        * As in the initial byte-based head/tail fill, each
+        * conditional below ensures that the subsequent offsets
+        * are valid (e.g. !(n<=24) implies n>=28). */
+
+       *(u32 *)(s+0) = c32;
+       *(u32 *)(s+n-4) = c32;
+       if (n <= 8) return dest;
+       *(u32 *)(s+4) = c32;
+       *(u32 *)(s+8) = c32;
+       *(u32 *)(s+n-12) = c32;
+       *(u32 *)(s+n-8) = c32;
+       if (n <= 24) return dest;
+       *(u32 *)(s+12) = c32;
+       *(u32 *)(s+16) = c32;
+       *(u32 *)(s+20) = c32;
+       *(u32 *)(s+24) = c32;
+       *(u32 *)(s+n-28) = c32;
+       *(u32 *)(s+n-24) = c32;
+       *(u32 *)(s+n-20) = c32;
+       *(u32 *)(s+n-16) = c32;
+
+       /* Align to a multiple of 8 so we can fill 64 bits at a time,
+        * and avoid writing the same bytes twice as much as is
+        * practical without introducing additional branching. */
+
+       k = 24 + ((uintptr_t)s & 4);
+       s += k;
+       n -= k;
+
+       /* If this loop is reached, 28 tail bytes have already been
+        * filled, so any remainder when n drops below 32 can be
+        * safely ignored. */
+
+       u64 c64 = c32 | ((u64)c32 << 32);
+       for (; n >= 32; n-=32, s+=32) {
+               *(u64 *)(s+0) = c64;
+               *(u64 *)(s+8) = c64;
+               *(u64 *)(s+16) = c64;
+               *(u64 *)(s+24) = c64;
        }
+#else
+       /* Pure C fallback with no aliasing violations. */
+       for (; n; n--, s++) *s = c;
+#endif
+
        return dest;
 }