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: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 15 deletions

diff --git a/lib/gen_crc32table.c b/lib/gen_crc32table.c
index bea5d97df991..85d0e412a04f 100644
--- a/lib/gen_crc32table.c
+++ b/lib/gen_crc32table.c
@@ -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");
         }