/*-*- 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 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/fmt/leb128.h"

/**
 * Decodes a GNU-style varint from a buffer.
 *
 * The GNU Assembler is able to encode numbers this way, since it's used
 * by the DWARF debug format.
 */
int unsleb128(const void *buf, size_t size, int128_t *out) {
  int b;
  int128_t r, w;
  unsigned char c;
  const unsigned char *p, *pe;
  pe = (p = buf) + size;
  r = b = 0;
  do {
    if (size && p == pe) return -1;
    c = *p++;
    w = c & 0x7f;
    r |= w << b;
    b += 7;
  } while (c & 0x80);
  if (c & 0x40) r |= -1ull << b;
  if (out) *out = r;
  return p - (const unsigned char *)buf;
}