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crc32: major optimization
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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

[[email protected]: coding-style fixes]
Signed-off-by: Joakim Tjernlund <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@joakim-tjernlund @torvalds
joakim-tjernlund authored and torvalds committed May 25, 2010
1 parent d4977c7 commit 836e2af
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Showing 2 changed files with 47 additions and 24 deletions.
24 changes: 15 additions & 9 deletions lib/crc32.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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 */
Expand All @@ -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
/**
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand Down
47 changes: 32 additions & 15 deletions lib/gen_crc32table.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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;
}
}
}

Expand All @@ -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 (i = 0; i < len - 1; i++) {
if (i % ENTRIES_PER_LINE == 0)
printf("\n");
printf("%s(0x%8.8xL), ", trans, table[i]);
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[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)
Expand All @@ -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");
}
Expand Down

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