fdchecksum32.c
Author: cmaier@cmassoc.net

    /*====================================================================*
     *
     *   uint32_t fdchecksum32 (int fd, size_t extent, uint32_t checksum);
     *
     *   memory.h
     *
     *   return the 32-bit checksum of a file region starting from the
     *   current file position; extent is specified in bytes but will be
     *   rounded to a multiple of four bytes;
     *
     *   Motley Tools by Charles Maier <cmaier@cmassoc.net>;
     *   Copyright (c) 2001-2006 by Charles Maier Associates;
     *   Licensed under the Internet Software Consortium License;
     *
     *--------------------------------------------------------------------*/

    #ifndef FDCHECKSUM32_SOURCE
    #define FDCHECKSUM32_SOURCE

    #include <stdio.h>
    #include <unistd.h>
    #include <errno.h>

    #include "../tools/memory.h"

    uint32_t fdchecksum32 (int fd, register size_t extent, register uint32_t checksum)

    {
    	uint32_t memory;
    	while (extent >= sizeof (memory))
    	{
    		if (read (fd, &memory, sizeof (memory)) != sizeof (memory))
    		{
    			return (-1);
    		}
    		extent -= sizeof (memory);
    		checksum ^= memory;
    	}
    	return (~checksum);
    }

    #endif

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