#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)
{
- /* pretend to succeed, but discard data */
+ 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 *s, size_t n, const char *fmt, va_list ap)
+int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
{
- int r;
- FILE f;
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,
+ };
- memset(&f, 0, sizeof(FILE));
- f.lbf = EOF;
- f.write = sn_write;
- f.buf_size = 1;
- f.buf = buf;
if (n > INT_MAX) {
errno = EOVERFLOW;
return -1;
- } else if (n > 0) {
- if (n > (char *)0+SIZE_MAX-s) n = (char *)0+SIZE_MAX-s;
- f.wpos = s;
- f.wbase = f.wend = s+n-1;
- f.wstop = f.wend - 1;
}
- r = vfprintf(&f, fmt, ap);
- /* wpos points just after last byte written, or to s+n-1 (wbase) */
- *f.wpos = 0;
- return r;
+
+ *c.s = 0;
+ return vfprintf(&f, fmt, ap);
}