#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <wchar.h>

#include "internal.h"

size_t mbsrtowcs(wchar_t* restrict ws, const char** restrict src, size_t wn,
                 mbstate_t* restrict st) {
  const unsigned char* s = (const void*)*src;
  size_t wn0 = wn;
  unsigned c = 0;

  if (st && (c = *(unsigned*)st)) {
    if (ws) {
      *(unsigned*)st = 0;
      goto resume;
    } else {
      goto resume0;
    }
  }

  if (MB_CUR_MAX == 1) {
    if (!ws)
      return strlen((const char*)s);
    for (;;) {
      if (!wn) {
        *src = (const void*)s;
        return wn0;
      }
      if (!*s)
        break;
      c = *s++;
      *ws++ = CODEUNIT(c);
      wn--;
    }
    *ws = 0;
    *src = 0;
    return wn0 - wn;
  }

  if (!ws)
    for (;;) {
      if (*s - 1u < 0x7f && (uintptr_t)s % 4 == 0) {
        while (!((*(uint32_t*)s | (*(uint32_t*)s - 0x01010101)) & 0x80808080)) {
          s += 4;
          wn -= 4;
        }
      }
      if (*s - 1u < 0x7f) {
        s++;
        wn--;
        continue;
      }
      if (*s - SA > SB - SA)
        break;
      c = bittab[*s++ - SA];
    resume0:
      if (OOB(c, *s)) {
        s--;
        break;
      }
      s++;
      if (c & (1U << 25)) {
        if (*s - 0x80u >= 0x40) {
          s -= 2;
          break;
        }
        s++;
        if (c & (1U << 19)) {
          if (*s - 0x80u >= 0x40) {
            s -= 3;
            break;
          }
          s++;
        }
      }
      wn--;
      c = 0;
    }
  else
    for (;;) {
      if (!wn) {
        *src = (const void*)s;
        return wn0;
      }
      if (*s - 1u < 0x7f && (uintptr_t)s % 4 == 0) {
        while (wn >= 5 && !((*(uint32_t*)s | (*(uint32_t*)s - 0x01010101)) & 0x80808080)) {
          *ws++ = *s++;
          *ws++ = *s++;
          *ws++ = *s++;
          *ws++ = *s++;
          wn -= 4;
        }
      }
      if (*s - 1u < 0x7f) {
        *ws++ = *s++;
        wn--;
        continue;
      }
      if (*s - SA > SB - SA)
        break;
      c = bittab[*s++ - SA];
    resume:
      if (OOB(c, *s)) {
        s--;
        break;
      }
      c = (c << 6) | (*s++ - 0x80);
      if (c & (1U << 31)) {
        if (*s - 0x80u >= 0x40) {
          s -= 2;
          break;
        }
        c = (c << 6) | (*s++ - 0x80);
        if (c & (1U << 31)) {
          if (*s - 0x80u >= 0x40) {
            s -= 3;
            break;
          }
          c = (c << 6) | (*s++ - 0x80);
        }
      }
      *ws++ = c;
      wn--;
      c = 0;
    }

  if (!c && !*s) {
    if (ws) {
      *ws = 0;
      *src = 0;
    }
    return wn0 - wn;
  }
  errno = EILSEQ;
  if (ws)
    *src = (const void*)s;
  return -1;
}