ich777/linux_media
1
0
Fork 0
mirror of https://github.com/tbsdtv/linux_media.git synced 2025-07-23 04:33:26 +02:00
Code Issues Packages Projects Releases Wiki Activity

crc32: major optimization

Browse Source 
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: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Joakim Tjernlund
2010-05-24 14:33:31 -07:00
committed by Linus Torvalds
parent d4977c78e9
commit 836e2af925
2 changed files with 47 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
lib/gen_crc32table.c
View File

@@ -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 (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)
@@ -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");
}