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Diffstat (limited to 'src/H5checksum.c')
| -rw-r--r-- | src/H5checksum.c | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/src/H5checksum.c b/src/H5checksum.c new file mode 100644 index 0000000..f4d702b --- /dev/null +++ b/src/H5checksum.c @@ -0,0 +1,145 @@ +/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * + * Copyright by the Board of Trustees of the University of Illinois. * + * All rights reserved. * + * * + * This file is part of HDF5. The full HDF5 copyright notice, including * + * terms governing use, modification, and redistribution, is contained in * + * the files COPYING and Copyright.html. COPYING can be found at the root * + * of the source code distribution tree; Copyright.html can be found at the * + * root level of an installed copy of the electronic HDF5 document set and * + * is linked from the top-level documents page. It can also be found at * + * http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html. If you do not have * + * access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. * + * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ + +/*------------------------------------------------------------------------- + * + * Created: H5checksum.c + * Aug 21 2006 + * Quincey Koziol <koziol@hdfgroup.org> + * + * Purpose: Internal code for computing fletcher32 checksums + * + *------------------------------------------------------------------------- + */ + +/****************/ +/* Module Setup */ +/****************/ + + +/***********/ +/* Headers */ +/***********/ +#include "H5private.h" /* Generic Functions */ + + +/****************/ +/* Local Macros */ +/****************/ + + +/******************/ +/* Local Typedefs */ +/******************/ + + +/********************/ +/* Package Typedefs */ +/********************/ + + +/********************/ +/* Local Prototypes */ +/********************/ + + +/*********************/ +/* Package Variables */ +/*********************/ + + +/*****************************/ +/* Library Private Variables */ +/*****************************/ + + +/*******************/ +/* Local Variables */ +/*******************/ + + + +/*------------------------------------------------------------------------- + * Function: H5_fletcher32 + * + * Purpose: This routine provides a generic, fast checksum algorithm for + * use in the library. + * + * Note: See the Wikipedia page for Fletcher's checksum: + * http://en.wikipedia.org/wiki/Fletcher%27s_checksum + * for more details, etc. + * + * Return: 32-bit fletcher checksum of input buffer (can't fail) + * + * Programmer: Quincey Koziol + * Monday, August 21, 2006 + * + *------------------------------------------------------------------------- + */ +uint32_t +H5_fletcher32(const void *_data, size_t _len) +{ + const uint16_t *data = (const uint16_t *)_data; /* Pointer to the data to be summed */ + size_t len = _len / 2; /* Length in 16-bit words */ + uint32_t sum1 = 0xffff, sum2 = 0xffff; + uint32_t ret_value; /* Return value */ + + FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_fletcher32) + + /* Sanity check */ + HDassert(_data); + HDassert(_len > 0); + + /* Compute checksum for pairs of bytes */ + /* The magic "360" value is is the largest number of sums that can be + * performed without numeric overflow. See the Wikipedia page for + * Fletcher's checksum: http://en.wikipedia.org/wiki/Fletcher%27s_checksum + * for more details, etc. + */ + while (len) { + unsigned tlen = len > 360 ? 360 : len; + len -= tlen; + do { + sum1 += *data++; + sum2 += sum1; + } while (--tlen); + sum1 = (sum1 & 0xffff) + (sum1 >> 16); + sum2 = (sum2 & 0xffff) + (sum2 >> 16); + } + + /* Check for odd # of bytes */ + if(_len % 2) { + sum1 += *(const uint8_t *)data; + sum2 += sum1; + sum1 = (sum1 & 0xffff) + (sum1 >> 16); + sum2 = (sum2 & 0xffff) + (sum2 >> 16); + } /* end if */ + + /* Second reduction step to reduce sums to 16 bits */ + sum1 = (sum1 & 0xffff) + (sum1 >> 16); + sum2 = (sum2 & 0xffff) + (sum2 >> 16); + +/* Byteswap result on little-endian platforms */ +#ifdef H5_WORDS_BIGENDIAN + ret_value = sum2 << 16 | sum1; +#else /* H5_WORDS_BIGENDIAN */ + ret_value = (sum2 << 8) & 0x00ff0000; + ret_value |= (sum2 << 24) & 0xff000000; + ret_value |= (sum1 << 8) & 0x0000ff00; + ret_value |= (sum1 >> 8) & 0x000000ff; +#endif /* H5_WORDS_BIGENDIAN */ + + FUNC_LEAVE_NOAPI(ret_value) +} /* end H5_fletcher32() */ + |