1 #include "stdio_impl.h"
2 #include <limits.h>
3 #include <string.h>
4 #include <errno.h>
5 #include <stdint.h>
6
7 struct cookie {
8 char *s;
9 size_t n;
10 };
11
12 #define MIN(a, b) ((a) < (b) ? (a) : (b))
13
sn_write(FILE * f,const unsigned char * s,size_t l)14 static size_t sn_write(FILE *f, const unsigned char *s, size_t l)
15 {
16 struct cookie *c = f->cookie;
17 size_t k = MIN(c->n, f->wpos - f->wbase);
18 if (k) {
19 memcpy(c->s, f->wbase, k);
20 c->s += k;
21 c->n -= k;
22 }
23 k = MIN(c->n, l);
24 if (k) {
25 memcpy(c->s, s, k);
26 c->s += k;
27 c->n -= k;
28 }
29 *c->s = 0;
30 f->wpos = f->wbase = f->buf;
31 /* pretend to succeed, even if we discarded extra data */
32 return l;
33 }
34
vsnprintf(char * restrict s,size_t n,const char * restrict fmt,va_list ap)35 int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
36 {
37 unsigned char buf[1];
38 char dummy[1];
39 struct cookie c = { .s = n ? s : dummy, .n = n ? n-1 : 0 };
40 FILE f = {
41 .lbf = EOF,
42 .write = sn_write,
43 .lock = -1,
44 .buf = buf,
45 .cookie = &c,
46 };
47
48 if (n > INT_MAX) {
49 errno = EOVERFLOW;
50 return -1;
51 }
52
53 *c.s = 0;
54 return vfprintf(&f, fmt, ap);
55 }
56