1 #include "libc.h"
2 #include <limits.h>
3 #include <stdint.h>
4 #include <string.h>
5
6 #define ALIGN (sizeof(size_t) - 1)
7 #define ONES ((size_t)-1 / UCHAR_MAX)
8 #define HIGHS (ONES * (UCHAR_MAX / 2 + 1))
9 #define HASZERO(x) (((x)-ONES) & ~(x)&HIGHS)
10
__stpncpy(char * restrict d,const char * restrict s,size_t n)11 char* __stpncpy(char* restrict d, const char* restrict s, size_t n) {
12 // This reads past the end of the string, which is usually OK since
13 // it won't cross a page boundary. But under ASan, even one byte
14 // past the actual end is diagnosed.
15 if (!__has_feature(address_sanitizer) &&
16 ((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
17 for (; ((uintptr_t)s & ALIGN) && n && (*d = *s); n--, s++, d++)
18 ;
19 if (!n || !*s)
20 goto tail;
21 size_t* wd = (void*)d;
22 const size_t* ws = (const void*)s;
23 for (; n >= sizeof(size_t) && !HASZERO(*ws); n -= sizeof(size_t), ws++, wd++)
24 *wd = *ws;
25 d = (void*)wd;
26 s = (const void*)ws;
27 }
28 for (; n && (*d = *s); n--, s++, d++)
29 ;
30 tail:
31 memset(d, 0, n);
32 return d;
33 }
34
35 weak_alias(__stpncpy, stpncpy);
36