/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 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.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#ifndef __COSMOPOLITAN__
#include <stdio.h>
#include <wchar.h>
#endif
#include "blc.h"

#define ThomPikeCont(x)     (0200 == (0300 & (x)))
#define ThomPikeByte(x)     ((x) & (((1 << ThomPikeMsb(x)) - 1) | 3))
#define ThomPikeLen(x)      (7 - ThomPikeMsb(x))
#define ThomPikeMsb(x)      ((255 & (x)) < 252 ? bsr(255 & ~(x)) : 1)
#define ThomPikeMerge(x, y) ((x) << 6 | 077 & (y))

static inline int bsr(uint64_t x) {
#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
  return __builtin_clzll(x) ^ 63;
#else
  static const char kDebruijn[64] = {
      0,  47, 1,  56, 48, 27, 2,  60, 57, 49, 41, 37, 28, 16, 3,  61,
      54, 58, 35, 52, 50, 42, 21, 44, 38, 32, 29, 23, 17, 11, 4,  62,
      46, 55, 26, 59, 40, 36, 15, 53, 34, 51, 20, 43, 31, 22, 10, 45,
      25, 39, 14, 33, 19, 30, 9,  24, 13, 18, 8,  12, 7,  6,  5,  63,
  };
  x |= x >> 1, x |= x >> 2;
  x |= x >> 4, x |= x >> 8;
  x |= x >> 16, x |= x >> 32;
  return kDebruijn[(x * 0x03f79d71b4cb0a89) >> 58];
#endif
}

wint_t fgetwc(FILE *f) {
  int c, n;
  wint_t b, x, y;
  if ((c = fgetc(f)) == EOF) return EOF;
  b = c;
  if (b < 0300) return b;
  n = ThomPikeLen(b);
  x = ThomPikeByte(b);
  while (--n) {
    if ((c = fgetc(f)) == EOF) return EOF;
    y = c;
    if (ThomPikeCont(y)) {
      x = ThomPikeMerge(x, y);
    } else {
      ungetc(y, f);
      return b;
    }
  }
  return x;
}