patch-2.4.22 linux-2.4.22/lib/crc32.c

Next file: linux-2.4.22/lib/crc32defs.h
Previous file: linux-2.4.22/lib/Makefile
Back to the patch index
Back to the overall index

diff -urN linux-2.4.21/lib/crc32.c linux-2.4.22/lib/crc32.c
@@ -0,0 +1,536 @@
+/* 
+ * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
+ * Nicer crc32 functions/docs submitted by linux@horizon.com.  Thanks!
+ *
+ * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
+ * Same crc32 function was used in 5 other places in the kernel.
+ * I made one version, and deleted the others.
+ * There are various incantations of crc32().  Some use a seed of 0 or ~0.
+ * Some xor at the end with ~0.  The generic crc32() function takes
+ * seed as an argument, and doesn't xor at the end.  Then individual
+ * users can do whatever they need.
+ *   drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
+ *   fs/jffs2 uses seed 0, doesn't xor with ~0.
+ *   fs/partitions/efi.c uses seed ~0, xor's with ~0.
+ * 
+ */
+
+#include <linux/crc32.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/config.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <asm/atomic.h>
+#include "crc32defs.h"
+#if CRC_LE_BITS == 8
+#define tole(x) __constant_cpu_to_le32(x)
+#define tobe(x) __constant_cpu_to_be32(x)
+#else
+#define tole(x) (x)
+#define tobe(x) (x)
+#endif
+#include "crc32table.h"
+
+#if __GNUC__ >= 3	/* 2.x has "attribute", but only 3.0 has "pure */
+#define attribute(x) __attribute__(x)
+#else
+#define attribute(x)
+#endif
+
+/*
+ * This code is in the public domain; copyright abandoned.
+ * Liability for non-performance of this code is limited to the amount
+ * you paid for it.  Since it is distributed for free, your refund will
+ * be very very small.  If it breaks, you get to keep both pieces.
+ */
+
+MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
+MODULE_DESCRIPTION("Ethernet CRC32 calculations");
+MODULE_LICENSE("GPL and additional rights");
+
+#if CRC_LE_BITS == 1
+/*
+ * In fact, the table-based code will work in this case, but it can be
+ * simplified by inlining the table in ?: form.
+ */
+
+/**
+ * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
+ * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
+ *        other uses, or the previous crc32 value if computing incrementally.
+ * @p   - pointer to buffer over which CRC is run
+ * @len - length of buffer @p
+ * 
+ */
+u32 attribute((pure)) crc32_le(u32 crc, unsigned char const *p, size_t len)
+{
+	int i;
+	while (len--) {
+		crc ^= *p++;
+		for (i = 0; i < 8; i++)
+			crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
+	}
+	return crc;
+}
+#else				/* Table-based approach */
+
+/**
+ * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
+ * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
+ *        other uses, or the previous crc32 value if computing incrementally.
+ * @p   - pointer to buffer over which CRC is run
+ * @len - length of buffer @p
+ * 
+ */
+u32 attribute((pure)) crc32_le(u32 crc, unsigned char const *p, size_t len)
+{
+# if CRC_LE_BITS == 8
+	const u32      *b =(u32 *)p;
+	const u32      *tab = crc32table_le;
+
+# ifdef __LITTLE_ENDIAN
+#  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
+# else
+#  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
+# endif
+
+	crc = __cpu_to_le32(crc);
+	/* Align it */
+	if(unlikely(((long)b)&3 && len)){
+		do {
+			DO_CRC(*((u8 *)b)++);
+		} while ((--len) && ((long)b)&3 );
+	}
+	if(likely(len >= 4)){
+		/* load data 32 bits wide, xor data 32 bits wide. */
+		size_t save_len = len & 3;
+	        len = len >> 2;
+		--b; /* use pre increment below(*++b) for speed */
+		do {
+			crc ^= *++b;
+			DO_CRC(0);
+			DO_CRC(0);
+			DO_CRC(0);
+			DO_CRC(0);
+		} while (--len);
+		b++; /* point to next byte(s) */
+		len = save_len;
+	}
+	/* And the last few bytes */
+	if(len){
+		do {
+			DO_CRC(*((u8 *)b)++);
+		} while (--len);
+	}
+
+	return __le32_to_cpu(crc);
+#undef ENDIAN_SHIFT
+#undef DO_CRC
+
+# elif CRC_LE_BITS == 4
+	while (len--) {
+		crc ^= *p++;
+		crc = (crc >> 4) ^ crc32table_le[crc & 15];
+		crc = (crc >> 4) ^ crc32table_le[crc & 15];
+	}
+	return crc;
+# elif CRC_LE_BITS == 2
+	while (len--) {
+		crc ^= *p++;
+		crc = (crc >> 2) ^ crc32table_le[crc & 3];
+		crc = (crc >> 2) ^ crc32table_le[crc & 3];
+		crc = (crc >> 2) ^ crc32table_le[crc & 3];
+		crc = (crc >> 2) ^ crc32table_le[crc & 3];
+	}
+	return crc;
+# endif
+}
+#endif
+
+#if CRC_BE_BITS == 1
+/*
+ * In fact, the table-based code will work in this case, but it can be
+ * simplified by inlining the table in ?: form.
+ */
+
+/**
+ * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
+ * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
+ *        other uses, or the previous crc32 value if computing incrementally.
+ * @p   - pointer to buffer over which CRC is run
+ * @len - length of buffer @p
+ * 
+ */
+u32 attribute((pure)) crc32_be(u32 crc, unsigned char const *p, size_t len)
+{
+	int i;
+	while (len--) {
+		crc ^= *p++ << 24;
+		for (i = 0; i < 8; i++)
+			crc =
+			    (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
+					  0);
+	}
+	return crc;
+}
+
+#else				/* Table-based approach */
+/**
+ * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
+ * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
+ *        other uses, or the previous crc32 value if computing incrementally.
+ * @p   - pointer to buffer over which CRC is run
+ * @len - length of buffer @p
+ * 
+ */
+u32 attribute((pure)) crc32_be(u32 crc, unsigned char const *p, size_t len)
+{
+# if CRC_BE_BITS == 8
+	const u32      *b =(u32 *)p;
+	const u32      *tab = crc32table_be;
+
+# ifdef __LITTLE_ENDIAN
+#  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
+# else
+#  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
+# endif
+
+	crc = __cpu_to_be32(crc);
+	/* Align it */
+	if(unlikely(((long)b)&3 && len)){
+		do {
+			DO_CRC(*((u8 *)b)++);
+		} while ((--len) && ((long)b)&3 );
+	}
+	if(likely(len >= 4)){
+		/* load data 32 bits wide, xor data 32 bits wide. */
+		size_t save_len = len & 3;
+	        len = len >> 2;
+		--b; /* use pre increment below(*++b) for speed */
+		do {
+			crc ^= *++b;
+			DO_CRC(0);
+			DO_CRC(0);
+			DO_CRC(0);
+			DO_CRC(0);
+		} while (--len);
+		b++; /* point to next byte(s) */
+		len = save_len;
+	}
+	/* And the last few bytes */
+	if(len){
+		do {
+			DO_CRC(*((u8 *)b)++);
+		} while (--len);
+	}
+	return __be32_to_cpu(crc);
+#undef ENDIAN_SHIFT
+#undef DO_CRC
+
+# elif CRC_BE_BITS == 4
+	while (len--) {
+		crc ^= *p++ << 24;
+		crc = (crc << 4) ^ crc32table_be[crc >> 28];
+		crc = (crc << 4) ^ crc32table_be[crc >> 28];
+	}
+	return crc;
+# elif CRC_BE_BITS == 2
+	while (len--) {
+		crc ^= *p++ << 24;
+		crc = (crc << 2) ^ crc32table_be[crc >> 30];
+		crc = (crc << 2) ^ crc32table_be[crc >> 30];
+		crc = (crc << 2) ^ crc32table_be[crc >> 30];
+		crc = (crc << 2) ^ crc32table_be[crc >> 30];
+	}
+	return crc;
+# endif
+}
+#endif
+
+u32 bitreverse(u32 x)
+{
+	x = (x >> 16) | (x << 16);
+	x = (x >> 8 & 0x00ff00ff) | (x << 8 & 0xff00ff00);
+	x = (x >> 4 & 0x0f0f0f0f) | (x << 4 & 0xf0f0f0f0);
+	x = (x >> 2 & 0x33333333) | (x << 2 & 0xcccccccc);
+	x = (x >> 1 & 0x55555555) | (x << 1 & 0xaaaaaaaa);
+	return x;
+}
+
+#ifndef CONFIG_CRC32 
+	/* To ensure that this file is pulled in from lib/lib.a if it's
+	   configured in but nothing in-kernel uses it, we export its
+	   symbols from kernel/ksyms.c in the CONFIG_CRC32=y case.
+	   Otherwise (either modular or pulled in by the makefile magic)
+	   we export them from here. */
+EXPORT_SYMBOL(crc32_le);
+EXPORT_SYMBOL(crc32_be);
+EXPORT_SYMBOL(bitreverse);
+#endif
+
+/*
+ * A brief CRC tutorial.
+ *
+ * A CRC is a long-division remainder.  You add the CRC to the message,
+ * and the whole thing (message+CRC) is a multiple of the given
+ * CRC polynomial.  To check the CRC, you can either check that the
+ * CRC matches the recomputed value, *or* you can check that the
+ * remainder computed on the message+CRC is 0.  This latter approach
+ * is used by a lot of hardware implementations, and is why so many
+ * protocols put the end-of-frame flag after the CRC.
+ *
+ * It's actually the same long division you learned in school, except that
+ * - We're working in binary, so the digits are only 0 and 1, and
+ * - When dividing polynomials, there are no carries.  Rather than add and
+ *   subtract, we just xor.  Thus, we tend to get a bit sloppy about
+ *   the difference between adding and subtracting.
+ *
+ * A 32-bit CRC polynomial is actually 33 bits long.  But since it's
+ * 33 bits long, bit 32 is always going to be set, so usually the CRC
+ * is written in hex with the most significant bit omitted.  (If you're
+ * familiar with the IEEE 754 floating-point format, it's the same idea.)
+ *
+ * Note that a CRC is computed over a string of *bits*, so you have
+ * to decide on the endianness of the bits within each byte.  To get
+ * the best error-detecting properties, this should correspond to the
+ * order they're actually sent.  For example, standard RS-232 serial is
+ * little-endian; the most significant bit (sometimes used for parity)
+ * is sent last.  And when appending a CRC word to a message, you should
+ * do it in the right order, matching the endianness.
+ *
+ * Just like with ordinary division, the remainder is always smaller than
+ * the divisor (the CRC polynomial) you're dividing by.  Each step of the
+ * division, you take one more digit (bit) of the dividend and append it
+ * to the current remainder.  Then you figure out the appropriate multiple
+ * of the divisor to subtract to being the remainder back into range.
+ * In binary, it's easy - it has to be either 0 or 1, and to make the
+ * XOR cancel, it's just a copy of bit 32 of the remainder.
+ *
+ * When computing a CRC, we don't care about the quotient, so we can
+ * throw the quotient bit away, but subtract the appropriate multiple of
+ * the polynomial from the remainder and we're back to where we started,
+ * ready to process the next bit.
+ *
+ * A big-endian CRC written this way would be coded like:
+ * for (i = 0; i < input_bits; i++) {
+ * 	multiple = remainder & 0x80000000 ? CRCPOLY : 0;
+ * 	remainder = (remainder << 1 | next_input_bit()) ^ multiple;
+ * }
+ * Notice how, to get at bit 32 of the shifted remainder, we look
+ * at bit 31 of the remainder *before* shifting it.
+ *
+ * But also notice how the next_input_bit() bits we're shifting into
+ * the remainder don't actually affect any decision-making until
+ * 32 bits later.  Thus, the first 32 cycles of this are pretty boring.
+ * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
+ * the end, so we have to add 32 extra cycles shifting in zeros at the
+ * end of every message,
+ *
+ * So the standard trick is to rearrage merging in the next_input_bit()
+ * until the moment it's needed.  Then the first 32 cycles can be precomputed,
+ * and merging in the final 32 zero bits to make room for the CRC can be
+ * skipped entirely.
+ * This changes the code to:
+ * for (i = 0; i < input_bits; i++) {
+ *      remainder ^= next_input_bit() << 31;
+ * 	multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
+ * 	remainder = (remainder << 1) ^ multiple;
+ * }
+ * With this optimization, the little-endian code is simpler:
+ * for (i = 0; i < input_bits; i++) {
+ *      remainder ^= next_input_bit();
+ * 	multiple = (remainder & 1) ? CRCPOLY : 0;
+ * 	remainder = (remainder >> 1) ^ multiple;
+ * }
+ *
+ * Note that the other details of endianness have been hidden in CRCPOLY
+ * (which must be bit-reversed) and next_input_bit().
+ *
+ * However, as long as next_input_bit is returning the bits in a sensible
+ * order, we can actually do the merging 8 or more bits at a time rather
+ * than one bit at a time:
+ * for (i = 0; i < input_bytes; i++) {
+ * 	remainder ^= next_input_byte() << 24;
+ * 	for (j = 0; j < 8; j++) {
+ * 		multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
+ * 		remainder = (remainder << 1) ^ multiple;
+ * 	}
+ * }
+ * Or in little-endian:
+ * for (i = 0; i < input_bytes; i++) {
+ * 	remainder ^= next_input_byte();
+ * 	for (j = 0; j < 8; j++) {
+ * 		multiple = (remainder & 1) ? CRCPOLY : 0;
+ * 		remainder = (remainder << 1) ^ multiple;
+ * 	}
+ * }
+ * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
+ * word at a time and increase the inner loop count to 32.
+ *
+ * You can also mix and match the two loop styles, for example doing the
+ * bulk of a message byte-at-a-time and adding bit-at-a-time processing
+ * for any fractional bytes at the end.
+ *
+ * The only remaining optimization is to the byte-at-a-time table method.
+ * Here, rather than just shifting one bit of the remainder to decide
+ * in the correct multiple to subtract, we can shift a byte at a time.
+ * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
+ * but again the multiple of the polynomial to subtract depends only on
+ * the high bits, the high 8 bits in this case.  
+ *
+ * The multile we need in that case is the low 32 bits of a 40-bit
+ * value whose high 8 bits are given, and which is a multiple of the
+ * generator polynomial.  This is simply the CRC-32 of the given
+ * one-byte message.
+ *
+ * Two more details: normally, appending zero bits to a message which
+ * is already a multiple of a polynomial produces a larger multiple of that
+ * polynomial.  To enable a CRC to detect this condition, it's common to
+ * invert the CRC before appending it.  This makes the remainder of the
+ * message+crc come out not as zero, but some fixed non-zero value.
+ *
+ * The same problem applies to zero bits prepended to the message, and
+ * a similar solution is used.  Instead of starting with a remainder of
+ * 0, an initial remainder of all ones is used.  As long as you start
+ * the same way on decoding, it doesn't make a difference.
+ */
+
+#if UNITTEST
+
+#include <stdlib.h>
+#include <stdio.h>
+
+#if 0				/*Not used at present */
+static void
+buf_dump(char const *prefix, unsigned char const *buf, size_t len)
+{
+	fputs(prefix, stdout);
+	while (len--)
+		printf(" %02x", *buf++);
+	putchar('\n');
+
+}
+#endif
+
+static void bytereverse(unsigned char *buf, size_t len)
+{
+	while (len--) {
+		unsigned char x = *buf;
+		x = (x >> 4) | (x << 4);
+		x = (x >> 2 & 0x33) | (x << 2 & 0xcc);
+		x = (x >> 1 & 0x55) | (x << 1 & 0xaa);
+		*buf++ = x;
+	}
+}
+
+static void random_garbage(unsigned char *buf, size_t len)
+{
+	while (len--)
+		*buf++ = (unsigned char) random();
+}
+
+#if 0				/* Not used at present */
+static void store_le(u32 x, unsigned char *buf)
+{
+	buf[0] = (unsigned char) x;
+	buf[1] = (unsigned char) (x >> 8);
+	buf[2] = (unsigned char) (x >> 16);
+	buf[3] = (unsigned char) (x >> 24);
+}
+#endif
+
+static void store_be(u32 x, unsigned char *buf)
+{
+	buf[0] = (unsigned char) (x >> 24);
+	buf[1] = (unsigned char) (x >> 16);
+	buf[2] = (unsigned char) (x >> 8);
+	buf[3] = (unsigned char) x;
+}
+
+/*
+ * This checks that CRC(buf + CRC(buf)) = 0, and that
+ * CRC commutes with bit-reversal.  This has the side effect
+ * of bytewise bit-reversing the input buffer, and returns
+ * the CRC of the reversed buffer.
+ */
+static u32 test_step(u32 init, unsigned char *buf, size_t len)
+{
+	u32 crc1, crc2;
+	size_t i;
+
+	crc1 = crc32_be(init, buf, len);
+	store_be(crc1, buf + len);
+	crc2 = crc32_be(init, buf, len + 4);
+	if (crc2)
+		printf("\nCRC cancellation fail: 0x%08x should be 0\n",
+		       crc2);
+
+	for (i = 0; i <= len + 4; i++) {
+		crc2 = crc32_be(init, buf, i);
+		crc2 = crc32_be(crc2, buf + i, len + 4 - i);
+		if (crc2)
+			printf("\nCRC split fail: 0x%08x\n", crc2);
+	}
+
+	/* Now swap it around for the other test */
+
+	bytereverse(buf, len + 4);
+	init = bitreverse(init);
+	crc2 = bitreverse(crc1);
+	if (crc1 != bitreverse(crc2))
+		printf("\nBit reversal fail: 0x%08x -> %0x08x -> 0x%08x\n",
+		       crc1, crc2, bitreverse(crc2));
+	crc1 = crc32_le(init, buf, len);
+	if (crc1 != crc2)
+		printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
+		       crc2);
+	crc2 = crc32_le(init, buf, len + 4);
+	if (crc2)
+		printf("\nCRC cancellation fail: 0x%08x should be 0\n",
+		       crc2);
+
+	for (i = 0; i <= len + 4; i++) {
+		crc2 = crc32_le(init, buf, i);
+		crc2 = crc32_le(crc2, buf + i, len + 4 - i);
+		if (crc2)
+			printf("\nCRC split fail: 0x%08x\n", crc2);
+	}
+
+	return crc1;
+}
+
+#define SIZE 64
+#define INIT1 0
+#define INIT2 0
+
+int main(void)
+{
+	unsigned char buf1[SIZE + 4];
+	unsigned char buf2[SIZE + 4];
+	unsigned char buf3[SIZE + 4];
+	int i, j;
+	u32 crc1, crc2, crc3;
+
+	for (i = 0; i <= SIZE; i++) {
+		printf("\rTesting length %d...", i);
+		fflush(stdout);
+		random_garbage(buf1, i);
+		random_garbage(buf2, i);
+		for (j = 0; j < i; j++)
+			buf3[j] = buf1[j] ^ buf2[j];
+
+		crc1 = test_step(INIT1, buf1, i);
+		crc2 = test_step(INIT2, buf2, i);
+		/* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
+		crc3 = test_step(INIT1 ^ INIT2, buf3, i);
+		if (crc3 != (crc1 ^ crc2))
+			printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
+			       crc3, crc1, crc2);
+	}
+	printf("\nAll test complete.  No failures expected.\n");
+	return 0;
+}
+
+#endif				/* UNITTEST */
FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)