[thirdparty/mdadm.git] / crc32.c

/* crc32.c -- compute the CRC-32 of a data stream
 * Copyright (C) 1995-2003 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 *
 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
 * tables for updating the shift register in one step with three exclusive-ors
 * instead of four steps with four exclusive-ors.  This results about a factor
 * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
 */

/* @(#) $Id$ */

/*
  Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  protection on the static variables used to control the first-use generation
  of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  first call get_crc_table() to initialize the tables before allowing more than
  one thread to use crc32().
 */

#ifdef MAKECRCH
#  include <stdio.h>
#  ifndef DYNAMIC_CRC_TABLE
#    define DYNAMIC_CRC_TABLE
#  endif /* !DYNAMIC_CRC_TABLE */
#endif /* MAKECRCH */

/* #include "zutil.h"      / * for STDC and FAR definitions */
#define STDC
#define FAR
#define Z_NULL ((void*)0)
#define OF(X) X
#define ZEXPORT
typedef long ptrdiff_t;
#define NOBYFOUR

#define local static

/* Find a four-byte integer type for crc32_little() and crc32_big(). */
#ifndef NOBYFOUR
#  ifdef STDC           /* need ANSI C limits.h to determine sizes */
#    include <limits.h>
#    define BYFOUR
#    if (UINT_MAX == 0xffffffffUL)
       typedef unsigned int u4;
#    else
#      if (ULONG_MAX == 0xffffffffUL)
         typedef unsigned long u4;
#      else
#        if (USHRT_MAX == 0xffffffffUL)
           typedef unsigned short u4;
#        else
#          undef BYFOUR     /* can't find a four-byte integer type! */
#        endif
#      endif
#    endif
#  endif /* STDC */
#endif /* !NOBYFOUR */

/* Definitions for doing the crc four data bytes at a time. */
#ifdef BYFOUR
#  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
                (((w)&0xff00)<<8)+(((w)&0xff)<<24))
   local unsigned long crc32_little OF((unsigned long,
                        const unsigned char FAR *, unsigned));
   local unsigned long crc32_big OF((unsigned long,
                        const unsigned char FAR *, unsigned));
#  define TBLS 8
#else
#  define TBLS 1
#endif /* BYFOUR */

#ifdef DYNAMIC_CRC_TABLE

local volatile int crc_table_empty = 1;
local unsigned long FAR crc_table[TBLS][256];
local void make_crc_table OF((void));
#ifdef MAKECRCH
   local void write_table OF((FILE *, const unsigned long FAR *));
#endif /* MAKECRCH */

/*
  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
  x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.

  Polynomials over GF(2) are represented in binary, one bit per coefficient,
  with the lowest powers in the most significant bit.  Then adding polynomials
  is just exclusive-or, and multiplying a polynomial by x is a right shift by
  one.  If we call the above polynomial p, and represent a byte as the
  polynomial q, also with the lowest power in the most significant bit (so the
  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
  where a mod b means the remainder after dividing a by b.

  This calculation is done using the shift-register method of multiplying and
  taking the remainder.  The register is initialized to zero, and for each
  incoming bit, x^32 is added mod p to the register if the bit is a one (where
  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
  x (which is shifting right by one and adding x^32 mod p if the bit shifted
  out is a one).  We start with the highest power (least significant bit) of
  q and repeat for all eight bits of q.

  The first table is simply the CRC of all possible eight bit values.  This is
  all the information needed to generate CRCs on data a byte at a time for all
  combinations of CRC register values and incoming bytes.  The remaining tables
  allow for word-at-a-time CRC calculation for both big-endian and little-
  endian machines, where a word is four bytes.
*/
local void make_crc_table()
{
    unsigned long c;
    int n, k;
    unsigned long poly;                 /* polynomial exclusive-or pattern */
    /* terms of polynomial defining this crc (except x^32): */
    static volatile int first = 1;      /* flag to limit concurrent making */
    static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

    /* See if another task is already doing this (not thread-safe, but better
       than nothing -- significantly reduces duration of vulnerability in
       case the advice about DYNAMIC_CRC_TABLE is ignored) */
    if (first) {
        first = 0;

        /* make exclusive-or pattern from polynomial (0xedb88320UL) */
        poly = 0UL;
        for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
            poly |= 1UL << (31 - p[n]);

        /* generate a crc for every 8-bit value */
        for (n = 0; n < 256; n++) {
            c = (unsigned long)n;
            for (k = 0; k < 8; k++)
                c = c & 1 ? poly ^ (c >> 1) : c >> 1;
            crc_table[0][n] = c;
        }

#ifdef BYFOUR
        /* generate crc for each value followed by one, two, and three zeros,
           and then the byte reversal of those as well as the first table */
        for (n = 0; n < 256; n++) {
            c = crc_table[0][n];
            crc_table[4][n] = REV(c);
            for (k = 1; k < 4; k++) {
                c = crc_table[0][c & 0xff] ^ (c >> 8);
                crc_table[k][n] = c;
                crc_table[k + 4][n] = REV(c);
            }
        }
#endif /* BYFOUR */

        crc_table_empty = 0;
    }
    else {      /* not first */
        /* wait for the other guy to finish (not efficient, but rare) */
        while (crc_table_empty)
            ;
    }

#ifdef MAKECRCH
    /* write out CRC tables to crc32.h */
    {
        FILE *out;

        out = fopen("crc32.h", "w");
        if (out == NULL) return;
        fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
        fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
        fprintf(out, "local const unsigned long FAR ");
        fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
        write_table(out, crc_table[0]);
#  ifdef BYFOUR
        fprintf(out, "#ifdef BYFOUR\n");
        for (k = 1; k < 8; k++) {
            fprintf(out, "  },\n  {\n");
            write_table(out, crc_table[k]);
        }
        fprintf(out, "#endif\n");
#  endif /* BYFOUR */
        fprintf(out, "  }\n};\n");
        fclose(out);
    }
#endif /* MAKECRCH */
}

#ifdef MAKECRCH
local void write_table(out, table)
    FILE *out;
    const unsigned long FAR *table;
{
    int n;

    for (n = 0; n < 256; n++)
        fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
                n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
}
#endif /* MAKECRCH */

#else /* !DYNAMIC_CRC_TABLE */
/* ========================================================================
 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 */
#include "crc32.h"
#endif /* DYNAMIC_CRC_TABLE */

/* =========================================================================
 * This function can be used by asm versions of crc32()
 */
const unsigned long FAR * ZEXPORT get_crc_table(void)
{
#ifdef DYNAMIC_CRC_TABLE
    if (crc_table_empty)
        make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
    return (const unsigned long FAR *)crc_table;
}

/* ========================================================================= */
#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1

/* ========================================================================= */
unsigned long ZEXPORT crc32(
	unsigned long crc,
	const unsigned char FAR *buf,
	unsigned len)
{
    if (buf == Z_NULL) return 0UL;

#ifdef DYNAMIC_CRC_TABLE
    if (crc_table_empty)
        make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */

#ifdef BYFOUR
    if (sizeof(void *) == sizeof(ptrdiff_t)) {
        u4 endian;

        endian = 1;
        if (*((unsigned char *)(&endian)))
            return crc32_little(crc, buf, len);
        else
            return crc32_big(crc, buf, len);
    }
#endif /* BYFOUR */
/*    crc = crc ^ 0xffffffffUL;*/
    while (len >= 8) {
        DO8;
        len -= 8;
    }
    if (len) do {
        DO1;
    } while (--len);
    return crc /* ^ 0xffffffffUL*/;
}

#ifdef BYFOUR

/* ========================================================================= */
#define DOLIT4 c ^= *buf4++; \
        c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
            crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4

/* ========================================================================= */
local unsigned long crc32_little(crc, buf, len)
    unsigned long crc;
    const unsigned char FAR *buf;
    unsigned len;
{
    register u4 c;
    register const u4 FAR *buf4;

    c = (u4)crc;
    c = ~c;
    while (len && ((ptrdiff_t)buf & 3)) {
        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
        len--;
    }

    buf4 = (const u4 FAR *)buf;
    while (len >= 32) {
        DOLIT32;
        len -= 32;
    }
    while (len >= 4) {
        DOLIT4;
        len -= 4;
    }
    buf = (const unsigned char FAR *)buf4;

    if (len) do {
        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
    } while (--len);
    c = ~c;
    return (unsigned long)c;
}

/* ========================================================================= */
#define DOBIG4 c ^= *++buf4; \
        c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
            crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4

/* ========================================================================= */
local unsigned long crc32_big(crc, buf, len)
    unsigned long crc;
    const unsigned char FAR *buf;
    unsigned len;
{
    register u4 c;
    register const u4 FAR *buf4;

    c = REV((u4)crc);
    c = ~c;
    while (len && ((ptrdiff_t)buf & 3)) {
        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
        len--;
    }

    buf4 = (const u4 FAR *)buf;
    buf4--;
    while (len >= 32) {
        DOBIG32;
        len -= 32;
    }
    while (len >= 4) {
        DOBIG4;
        len -= 4;
    }
    buf4++;
    buf = (const unsigned char FAR *)buf4;

    if (len) do {
        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
    } while (--len);
    c = ~c;
    return (unsigned long)(REV(c));
}

#endif /* BYFOUR */
Commit	Line	Data
11fcec12 NB	1	/* crc32.c -- compute the CRC-32 of a data stream
	2	* Copyright (C) 1995-2003 Mark Adler
	3	* For conditions of distribution and use, see copyright notice in zlib.h
	4	*
	5	* Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
	6	* CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
	7	* tables for updating the shift register in one step with three exclusive-ors
	8	* instead of four steps with four exclusive-ors. This results about a factor
	9	* of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
	10	*/
	11
	12	/* @(#) $Id$ */
	13
	14	/*
	15	Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
	16	protection on the static variables used to control the first-use generation
	17	of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
	18	first call get_crc_table() to initialize the tables before allowing more than
	19	one thread to use crc32().
	20	*/
	21
	22	#ifdef MAKECRCH
	23	# include <stdio.h>
	24	# ifndef DYNAMIC_CRC_TABLE
	25	# define DYNAMIC_CRC_TABLE
	26	# endif /* !DYNAMIC_CRC_TABLE */
	27	#endif /* MAKECRCH */
	28
	29	/* #include "zutil.h" / * for STDC and FAR definitions */
	30	#define STDC
	31	#define FAR
	32	#define Z_NULL ((void*)0)
	33	#define OF(X) X
	34	#define ZEXPORT
	35	typedef long ptrdiff_t;
	36	#define NOBYFOUR
	37
	38	#define local static
	39
	40	/* Find a four-byte integer type for crc32_little() and crc32_big(). */
	41	#ifndef NOBYFOUR
	42	# ifdef STDC /* need ANSI C limits.h to determine sizes */
	43	# include <limits.h>
	44	# define BYFOUR
	45	# if (UINT_MAX == 0xffffffffUL)
	46	typedef unsigned int u4;
	47	# else
	48	# if (ULONG_MAX == 0xffffffffUL)
	49	typedef unsigned long u4;
	50	# else
	51	# if (USHRT_MAX == 0xffffffffUL)
	52	typedef unsigned short u4;
	53	# else
	54	# undef BYFOUR /* can't find a four-byte integer type! */
	55	# endif
	56	# endif
	57	# endif
	58	# endif /* STDC */
	59	#endif /* !NOBYFOUR */
	60
	61	/* Definitions for doing the crc four data bytes at a time. */
	62	#ifdef BYFOUR
	63	# define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
	64	(((w)&0xff00)<<8)+(((w)&0xff)<<24))
65	local unsigned long crc32_little OF((unsigned long,
66	const unsigned char FAR *, unsigned));
67	local unsigned long crc32_big OF((unsigned long,
68	const unsigned char FAR *, unsigned));
69	# define TBLS 8
70	#else
71	# define TBLS 1
72	#endif /* BYFOUR */
73
74	#ifdef DYNAMIC_CRC_TABLE
75
76	local volatile int crc_table_empty = 1;
77	local unsigned long FAR crc_table[TBLS][256];
78	local void make_crc_table OF((void));
79	#ifdef MAKECRCH
80	local void write_table OF((FILE , const unsigned long FAR ));
81	#endif /* MAKECRCH */
82
83	/*
84	Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
85	x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
86
87	Polynomials over GF(2) are represented in binary, one bit per coefficient,
88	with the lowest powers in the most significant bit. Then adding polynomials
89	is just exclusive-or, and multiplying a polynomial by x is a right shift by
90	one. If we call the above polynomial p, and represent a byte as the
91	polynomial q, also with the lowest power in the most significant bit (so the
92	byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
93	where a mod b means the remainder after dividing a by b.
94
95	This calculation is done using the shift-register method of multiplying and
96	taking the remainder. The register is initialized to zero, and for each
97	incoming bit, x^32 is added mod p to the register if the bit is a one (where
98	x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
99	x (which is shifting right by one and adding x^32 mod p if the bit shifted
100	out is a one). We start with the highest power (least significant bit) of
101	q and repeat for all eight bits of q.
102
103	The first table is simply the CRC of all possible eight bit values. This is
104	all the information needed to generate CRCs on data a byte at a time for all
105	combinations of CRC register values and incoming bytes. The remaining tables
106	allow for word-at-a-time CRC calculation for both big-endian and little-
107	endian machines, where a word is four bytes.
108	*/
109	local void make_crc_table()
110	{
111	unsigned long c;
112	int n, k;
113	unsigned long poly; /* polynomial exclusive-or pattern */
114	/* terms of polynomial defining this crc (except x^32): */
115	static volatile int first = 1; /* flag to limit concurrent making */
116	static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
117
118	/* See if another task is already doing this (not thread-safe, but better
119	than nothing -- significantly reduces duration of vulnerability in
120	case the advice about DYNAMIC_CRC_TABLE is ignored) */
121	if (first) {
122	first = 0;
123
124	/* make exclusive-or pattern from polynomial (0xedb88320UL) */
125	poly = 0UL;
126	for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
127	poly \|= 1UL << (31 - p[n]);
128
129	/* generate a crc for every 8-bit value */
130	for (n = 0; n < 256; n++) {
131	c = (unsigned long)n;
132	for (k = 0; k < 8; k++)
133	c = c & 1 ? poly ^ (c >> 1) : c >> 1;
134	crc_table[0][n] = c;
135	}
136
137	#ifdef BYFOUR
138	/* generate crc for each value followed by one, two, and three zeros,
139	and then the byte reversal of those as well as the first table */
140	for (n = 0; n < 256; n++) {
141	c = crc_table[0][n];
142	crc_table[4][n] = REV(c);
143	for (k = 1; k < 4; k++) {
144	c = crc_table[0][c & 0xff] ^ (c >> 8);
145	crc_table[k][n] = c;
146	crc_table[k + 4][n] = REV(c);
147	}
148	}
149	#endif /* BYFOUR */
150
151	crc_table_empty = 0;
152	}
153	else { /* not first */
154	/* wait for the other guy to finish (not efficient, but rare) */
155	while (crc_table_empty)
156	;
157	}
158
159	#ifdef MAKECRCH
160	/* write out CRC tables to crc32.h */
161	{
162	FILE *out;
163
164	out = fopen("crc32.h", "w");
165	if (out == NULL) return;
166	fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
167	fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
168	fprintf(out, "local const unsigned long FAR ");
169	fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
170	write_table(out, crc_table[0]);
171	# ifdef BYFOUR
172	fprintf(out, "#ifdef BYFOUR\n");
173	for (k = 1; k < 8; k++) {
174	fprintf(out, " },\n {\n");
175	write_table(out, crc_table[k]);
176	}
177	fprintf(out, "#endif\n");
178	# endif /* BYFOUR */
179	fprintf(out, " }\n};\n");
180	fclose(out);
181	}
182	#endif /* MAKECRCH */
183	}
184
185	#ifdef MAKECRCH
186	local void write_table(out, table)
187	FILE *out;
188	const unsigned long FAR *table;
189	{
190	int n;
191
192	for (n = 0; n < 256; n++)
193	fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
194	n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
195	}
196	#endif /* MAKECRCH */
197
198	#else /* !DYNAMIC_CRC_TABLE */
199	/* ========================================================================
200	* Tables of CRC-32s of all single-byte values, made by make_crc_table().
201	*/
202	#include "crc32.h"
203	#endif /* DYNAMIC_CRC_TABLE */
204
205	/* =========================================================================
206	* This function can be used by asm versions of crc32()
207	*/
208	const unsigned long FAR * ZEXPORT get_crc_table(void)
209	{
210	#ifdef DYNAMIC_CRC_TABLE
211	if (crc_table_empty)
212	make_crc_table();
213	#endif /* DYNAMIC_CRC_TABLE */
214	return (const unsigned long FAR *)crc_table;
215	}
216
217	/* ========================================================================= */
218	#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
219	#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
220
221	/* ========================================================================= */
222	unsigned long ZEXPORT crc32(
223	unsigned long crc,
224	const unsigned char FAR *buf,
225	unsigned len)
226	{
227	if (buf == Z_NULL) return 0UL;
228
229	#ifdef DYNAMIC_CRC_TABLE
230	if (crc_table_empty)
231	make_crc_table();
232	#endif /* DYNAMIC_CRC_TABLE */
233
234	#ifdef BYFOUR
235	if (sizeof(void *) == sizeof(ptrdiff_t)) {
236	u4 endian;
237
238	endian = 1;
239	if (((unsigned char )(&endian)))
240	return crc32_little(crc, buf, len);
241	else
242	return crc32_big(crc, buf, len);
243	}
244	#endif /* BYFOUR */
245	/* crc = crc ^ 0xffffffffUL;*/
246	while (len >= 8) {
247	DO8;
248	len -= 8;
249	}
250	if (len) do {
251	DO1;
252	} while (--len);
253	return crc /* ^ 0xffffffffUL*/;
254	}
255
256	#ifdef BYFOUR
257
258	/* ========================================================================= */
259	#define DOLIT4 c ^= *buf4++; \
260	c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
261	crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
262	#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
263
264	/* ========================================================================= */
265	local unsigned long crc32_little(crc, buf, len)
266	unsigned long crc;
267	const unsigned char FAR *buf;
268	unsigned len;
269	{
270	register u4 c;
271	register const u4 FAR *buf4;
272
273	c = (u4)crc;
274	c = ~c;
275	while (len && ((ptrdiff_t)buf & 3)) {
276	c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
277	len--;
278	}
279
280	buf4 = (const u4 FAR *)buf;
281	while (len >= 32) {
282	DOLIT32;
283	len -= 32;
284	}
285	while (len >= 4) {
286	DOLIT4;
287	len -= 4;
288	}
289	buf = (const unsigned char FAR *)buf4;
290
291	if (len) do {
292	c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
293	} while (--len);
294	c = ~c;
295	return (unsigned long)c;
296	}
297
298	/* ========================================================================= */
299	#define DOBIG4 c ^= *++buf4; \
300	c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
301	crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
302	#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
303
304	/* ========================================================================= */
305	local unsigned long crc32_big(crc, buf, len)
306	unsigned long crc;
307	const unsigned char FAR *buf;
308	unsigned len;
309	{
310	register u4 c;
311	register const u4 FAR *buf4;
312
313	c = REV((u4)crc);
314	c = ~c;
315	while (len && ((ptrdiff_t)buf & 3)) {
316	c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
317	len--;
318	}
319
320	buf4 = (const u4 FAR *)buf;
321	buf4--;
322	while (len >= 32) {
323	DOBIG32;
324	len -= 32;
325	}
326	while (len >= 4) {
327	DOBIG4;
328	len -= 4;
329	}
330	buf4++;
331	buf = (const unsigned char FAR *)buf4;
332
333	if (len) do {
334	c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
335	} while (--len);
336	c = ~c;
337	return (unsigned long)(REV(c));
338	}
339
340	#endif /* BYFOUR */