cosmopolitan/libc/stdio/ungetwc.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=8 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/stdio/stdio.h"
#include "libc/str/str.h"
#include "libc/str/tpenc.h"

/**
 * Pushes wide character back to stream.
 */
wint_t ungetwc_unlocked(wint_t c, FILE *f) {
  char b[6];
  unsigned n;
  uint64_t w;
  if (c == -1) return -1;
  n = 0;
  w = tpenc(c);
  do {
    b[n++] = w;
  } while ((w >>= 8));
  if (f->beg >= n) {
    f->beg -= n;
    memcpy(f->buf + f->beg, b, n);
  } else if (f->beg + f->end + n <= f->size) {
    memmove(f->buf + f->beg + n, f->buf + f->beg, f->end - f->beg);
    memcpy(f->buf + f->beg, b, n);
    f->end += n;
  } else {
    return -1;
  }
  return c;
}