42 lines
847 B
C
42 lines
847 B
C
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#include <stdio.h>
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#include <limits.h>
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#include <string.h>
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#include <errno.h>
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#include <stdint.h>
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static size_t sn_write(FILE *f, const char *s, size_t l)
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{
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size_t k = f->wend - f->wpos;
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if (k > l) k = l;
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memcpy(f->wpos, s, k);
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f->wpos += k;
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/* pretend to succeed, but discard extra data */
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return l;
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}
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int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
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{
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int r;
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char b;
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FILE f = { .write = sn_write };
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if (n-1 > INT_MAX-1) {
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if (n) {
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errno = EOVERFLOW;
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return -1;
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}
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s = &b;
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n = 1;
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}
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/* Ensure pointers don't wrap if "infinite" n is passed in */
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if (n > (char *)0+SIZE_MAX-s-1) n = (char *)0+SIZE_MAX-s-1;
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f.wpos = s;
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f.wend = (s+n);
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r = vfprintf(&f, fmt, ap);
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/* Null-terminate, overwriting last char if dest buffer is full */
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if (n) f.wpos[-(f.wpos == f.wend)] = 0;
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return r;
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}
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