circuitpython/lib/uzlib/crc32.c

/*
 * CRC32 checksum
 *
 * Copyright (c) 1998-2003 by Joergen Ibsen / Jibz
 * All Rights Reserved
 *
 * http://www.ibsensoftware.com/
 *
 * This software is provided 'as-is', without any express
 * or implied warranty.  In no event will the authors be
 * held liable for any damages arising from the use of
 * this software.
 *
 * Permission is granted to anyone to use this software
 * for any purpose, including commercial applications,
 * and to alter it and redistribute it freely, subject to
 * the following restrictions:
 *
 * 1. The origin of this software must not be
 *    misrepresented; you must not claim that you
 *    wrote the original software. If you use this
 *    software in a product, an acknowledgment in
 *    the product documentation would be appreciated
 *    but is not required.
 *
 * 2. Altered source versions must be plainly marked
 *    as such, and must not be misrepresented as
 *    being the original software.
 *
 * 3. This notice may not be removed or altered from
 *    any source distribution.
 */

/*
 * CRC32 algorithm taken from the zlib source, which is
 * Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
 */

#include "tinf.h"

static const unsigned int tinf_crc32tab[16] = {
   0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190,
   0x6b6b51f4, 0x4db26158, 0x5005713c, 0xedb88320, 0xf00f9344,
   0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278,
   0xbdbdf21c
};

/* crc is previous value for incremental computation, 0xffffffff initially */
uint32_t uzlib_crc32(const void *data, unsigned int length, uint32_t crc)
{
   const unsigned char *buf = (const unsigned char *)data;
   unsigned int i;

   for (i = 0; i < length; ++i)
   {
      crc ^= buf[i];
      crc = tinf_crc32tab[crc & 0x0f] ^ (crc >> 4);
      crc = tinf_crc32tab[crc & 0x0f] ^ (crc >> 4);
   }

   // return value suitable for passing in next time, for final value invert it
   return crc/* ^ 0xffffffff*/;
}