checksum.c   [plain text]


/*
 * Routines to support checksumming of bytes.
 *
 * Copyright (C) 1996 Andrew Tridgell
 * Copyright (C) 1996 Paul Mackerras
 * Copyright (C) 2004, 2005 Wayne Davison
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "rsync.h"

int csum_length=2; /* initial value */

#define CSUM_CHUNK 64

extern int checksum_seed;
extern int protocol_version;

/*
  a simple 32 bit checksum that can be upadted from either end
  (inspired by Mark Adler's Adler-32 checksum)
  */
uint32 get_checksum1(char *buf1, int32 len)
{
    int32 i;
    uint32 s1, s2;
    schar *buf = (schar *)buf1;

    s1 = s2 = 0;
    for (i = 0; i < (len-4); i+=4) {
	s2 += 4*(s1 + buf[i]) + 3*buf[i+1] + 2*buf[i+2] + buf[i+3] +
	  10*CHAR_OFFSET;
	s1 += (buf[i+0] + buf[i+1] + buf[i+2] + buf[i+3] + 4*CHAR_OFFSET);
    }
    for (; i < len; i++) {
	s1 += (buf[i]+CHAR_OFFSET); s2 += s1;
    }
    return (s1 & 0xffff) + (s2 << 16);
}


void get_checksum2(char *buf, int32 len, char *sum)
{
	int32 i;
	static char *buf1;
	static int32 len1;
	struct mdfour m;

	if (len > len1) {
		if (buf1)
			free(buf1);
		buf1 = new_array(char, len+4);
		len1 = len;
		if (!buf1)
			out_of_memory("get_checksum2");
	}

	mdfour_begin(&m);

	memcpy(buf1,buf,len);
	if (checksum_seed) {
		SIVAL(buf1,len,checksum_seed);
		len += 4;
	}

	for(i = 0; i + CSUM_CHUNK <= len; i += CSUM_CHUNK) {
		mdfour_update(&m, (uchar *)(buf1+i), CSUM_CHUNK);
	}
	/*
	 * Prior to version 27 an incorrect MD4 checksum was computed
	 * by failing to call mdfour_tail() for block sizes that
	 * are multiples of 64.  This is fixed by calling mdfour_update()
	 * even when there are no more bytes.
	 */
	if (len - i > 0 || protocol_version >= 27) {
		mdfour_update(&m, (uchar *)(buf1+i), (len-i));
	}

	mdfour_result(&m, (uchar *)sum);
}


void file_checksum(char *fname,char *sum,OFF_T size)
{
	OFF_T i;
	struct map_struct *buf;
	int fd;
	OFF_T len = size;
	struct mdfour m;

	memset(sum,0,MD4_SUM_LENGTH);

	fd = do_open(fname, O_RDONLY, 0);
	if (fd == -1)
		return;

	buf = map_file(fd, size, MAX_MAP_SIZE, CSUM_CHUNK);

	mdfour_begin(&m);

	for(i = 0; i + CSUM_CHUNK <= len; i += CSUM_CHUNK) {
		mdfour_update(&m, (uchar *)map_ptr(buf, i, CSUM_CHUNK),
			      CSUM_CHUNK);
	}

	/* Prior to version 27 an incorrect MD4 checksum was computed
	 * by failing to call mdfour_tail() for block sizes that
	 * are multiples of 64.  This is fixed by calling mdfour_update()
	 * even when there are no more bytes. */
	if (len - i > 0 || protocol_version >= 27)
		mdfour_update(&m, (uchar *)map_ptr(buf, i, len-i), len-i);

	mdfour_result(&m, (uchar *)sum);

	close(fd);
	unmap_file(buf);
}


static int32 sumresidue;
static char sumrbuf[CSUM_CHUNK];
static struct mdfour md;

void sum_init(int seed)
{
	char s[4];
	mdfour_begin(&md);
	sumresidue = 0;
	SIVAL(s, 0, seed);
	sum_update(s, 4);
}

/**
 * Feed data into an MD4 accumulator, md.  The results may be
 * retrieved using sum_end().  md is used for different purposes at
 * different points during execution.
 *
 * @todo Perhaps get rid of md and just pass in the address each time.
 * Very slightly clearer and slower.
 **/
void sum_update(char *p, int32 len)
{
	if (len + sumresidue < CSUM_CHUNK) {
		memcpy(sumrbuf + sumresidue, p, len);
		sumresidue += len;
		return;
	}

	if (sumresidue) {
		int32 i = CSUM_CHUNK - sumresidue;
		memcpy(sumrbuf + sumresidue, p, i);
		mdfour_update(&md, (uchar *)sumrbuf, CSUM_CHUNK);
		len -= i;
		p += i;
	}

	while (len >= CSUM_CHUNK) {
		mdfour_update(&md, (uchar *)p, CSUM_CHUNK);
		len -= CSUM_CHUNK;
		p += CSUM_CHUNK;
	}

	sumresidue = len;
	if (sumresidue)
		memcpy(sumrbuf, p, sumresidue);
}

void sum_end(char *sum)
{
	if (sumresidue || protocol_version >= 27)
		mdfour_update(&md, (uchar *)sumrbuf, sumresidue);

	mdfour_result(&md, (uchar *)sum);
}