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#include "stdio_impl.h"
#include <limits.h>
#include <string.h>
#include <errno.h>
#include <stdint.h>
struct cookie {
char *s;
size_t n;
};
#define MIN(a, b) ((a) < (b) ? (a) : (b))
static size_t sn_write(FILE *f, const unsigned char *s, size_t l)
{
struct cookie *c = f->cookie;
size_t k = MIN(c->n, f->wpos - f->wbase);
if (k) {
memcpy(c->s, f->wbase, k);
c->s += k;
c->n -= k;
}
k = MIN(c->n, l);
if (k) {
memcpy(c->s, s, k);
c->s += k;
c->n -= k;
}
*c->s = 0;
f->wpos = f->wbase = f->buf;
/* pretend to succeed, even if we discarded extra data */
return l;
}
int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
{
unsigned char buf[1];
char dummy[1];
struct cookie c = { .s = n ? s : dummy, .n = n ? n-1 : 0 };
FILE f = {
.lbf = EOF,
.write = sn_write,
.lock = -1,
.buf = buf,
.cookie = &c,
};
if (n > INT_MAX) {
errno = EOVERFLOW;
return -1;
}
*c.s = 0;
return vfprintf(&f, fmt, ap);
}
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