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Commit 836e2af9 authored by Joakim Tjernlund's avatar Joakim Tjernlund Committed by Linus Torvalds
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crc32: major optimization 



Precompute more crc32 values(0xcc00, 0xcc0000 and 0xcc000000) into tables.
 This increases the table size from 1KB to 4KB but the performance benfit
makes it worth it:

28% faster on MPC8321, 266 MHz
2x faster on Core 2 Duo, 3.1GHz

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarJoakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d4977c78

lib/crc32.c

+15 −9
Original line number Diff line number Diff line
@@ -48,12 +48,20 @@ MODULE_LICENSE("GPL"); 
#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8



static inline u32

crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab)

crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])

{

# ifdef __LITTLE_ENDIAN

#  define DO_CRC(x) crc = tab[(crc ^ (x)) & 255 ] ^ (crc >> 8)

#  define DO_CRC(x) crc = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)

#  define DO_CRC4 crc = tab[3][(crc) & 255] ^ \

		tab[2][(crc >> 8) & 255] ^ \

		tab[1][(crc >> 16) & 255] ^ \

		tab[0][(crc >> 24) & 255]

# else

#  define DO_CRC(x) crc = tab[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)

#  define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)

#  define DO_CRC4 crc = tab[0][(crc) & 255] ^ \

		tab[1][(crc >> 8) & 255] ^ \

		tab[2][(crc >> 16) & 255] ^ \

		tab[3][(crc >> 24) & 255]

# endif

	const u32 *b;

	size_t    rem_len;
@@ -70,10 +78,7 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab) 
	b = (const u32 *)buf;

	for (--b; len; --len) {

		crc ^= *++b; /* use pre increment for speed */

		DO_CRC(0);

		DO_CRC(0);

		DO_CRC(0);

		DO_CRC(0);

		DO_CRC4;

	}

	len = rem_len;

	/* And the last few bytes */
@@ -85,6 +90,7 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab) 
	}

	return crc;

#undef DO_CRC

#undef DO_CRC4

}

#endif

/**
@@ -117,7 +123,7 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len) 
u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)

{

# if CRC_LE_BITS == 8

	const u32      *tab = crc32table_le;

	const u32      (*tab)[] = crc32table_le;



	crc = __cpu_to_le32(crc);

	crc = crc32_body(crc, p, len, tab);
@@ -174,7 +180,7 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len) 
u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)

{

# if CRC_BE_BITS == 8

	const u32      *tab = crc32table_be;

	const u32      (*tab)[] = crc32table_be;



	crc = __cpu_to_be32(crc);

	crc = crc32_body(crc, p, len, tab);

lib/gen_crc32table.c

+32 −15
Original line number Diff line number Diff line
@@ -7,8 +7,8 @@ 
#define LE_TABLE_SIZE (1 << CRC_LE_BITS)

#define BE_TABLE_SIZE (1 << CRC_BE_BITS)



static uint32_t crc32table_le[LE_TABLE_SIZE];

static uint32_t crc32table_be[BE_TABLE_SIZE];

static uint32_t crc32table_le[4][LE_TABLE_SIZE];

static uint32_t crc32table_be[4][BE_TABLE_SIZE];



/**

 * crc32init_le() - allocate and initialize LE table data
@@ -22,12 +22,19 @@ static void crc32init_le(void) 
	unsigned i, j;

	uint32_t crc = 1;



	crc32table_le[0] = 0;

	crc32table_le[0][0] = 0;



	for (i = 1 << (CRC_LE_BITS - 1); i; i >>= 1) {

		crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);

		for (j = 0; j < LE_TABLE_SIZE; j += 2 * i)

			crc32table_le[i + j] = crc ^ crc32table_le[j];

			crc32table_le[0][i + j] = crc ^ crc32table_le[0][j];

	}

	for (i = 0; i < LE_TABLE_SIZE; i++) {

		crc = crc32table_le[0][i];

		for (j = 1; j < 4; j++) {

			crc = crc32table_le[0][crc & 0xff] ^ (crc >> 8);

			crc32table_le[j][i] = crc;

		}

	}

}
@@ -39,25 +46,35 @@ static void crc32init_be(void) 
	unsigned i, j;

	uint32_t crc = 0x80000000;



	crc32table_be[0] = 0;

	crc32table_be[0][0] = 0;



	for (i = 1; i < BE_TABLE_SIZE; i <<= 1) {

		crc = (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE : 0);

		for (j = 0; j < i; j++)

			crc32table_be[i + j] = crc ^ crc32table_be[j];

			crc32table_be[0][i + j] = crc ^ crc32table_be[0][j];

	}

	for (i = 0; i < BE_TABLE_SIZE; i++) {

		crc = crc32table_be[0][i];

		for (j = 1; j < 4; j++) {

			crc = crc32table_be[0][(crc >> 24) & 0xff] ^ (crc << 8);

			crc32table_be[j][i] = crc;

		}

	}

}



static void output_table(uint32_t table[], int len, char *trans)

static void output_table(uint32_t table[4][256], int len, char *trans)

{

	int i;

	int i, j;



	for (j = 0 ; j < 4; j++) {

		printf("{");

		for (i = 0; i < len - 1; i++) {

			if (i % ENTRIES_PER_LINE == 0)

				printf("\n");

		printf("%s(0x%8.8xL), ", trans, table[i]);

			printf("%s(0x%8.8xL), ", trans, table[j][i]);

		}

		printf("%s(0x%8.8xL)},\n", trans, table[j][len - 1]);

	}

	printf("%s(0x%8.8xL)\n", trans, table[len - 1]);

}



int main(int argc, char** argv)
@@ -66,14 +83,14 @@ int main(int argc, char** argv) 


	if (CRC_LE_BITS > 1) {

		crc32init_le();

		printf("static const u32 crc32table_le[] = {");

		printf("static const u32 crc32table_le[4][256] = {");

		output_table(crc32table_le, LE_TABLE_SIZE, "tole");

		printf("};\n");

	}



	if (CRC_BE_BITS > 1) {

		crc32init_be();

		printf("static const u32 crc32table_be[] = {");

		printf("static const u32 crc32table_be[4][256] = {");

		output_table(crc32table_be, BE_TABLE_SIZE, "tobe");

		printf("};\n");

	}