Re: [PATCH v6 08/10] crc32-add-slicing-by-8.diff

Bob Pearson
2011-09-01T03:03:25Z

I've been looking at this stuff for too long! I just noticed that
crc32_body incorrectly always uses CRC_LE_BITS to pick algorithm.
Replace with a function parameter that will get optimized out
by the compiler since crc32_body is inlined.

add slicing-by-8 algorithm to the existing
slicing-by-4 algorithm. This consists of:
- extend largest BITS size from 32 to 64
- extend tables from tab[4][256] to up to tab[8][256]
- Add code for inner loop.

Signed-off-by: Bob Pearson <rpearson@systemfabricworks.com>

---
lib/crc32.c | 51 ++++++++++++++++++++++++++++++++++-----------------
lib/crc32defs.h | 29 +++++++++++++++++++++--------
lib/gen_crc32table.c | 43 +++++++++++++++++++++++++++----------------
3 files changed, 82 insertions(+), 41 deletions(-)

Index: for-next/lib/crc32.c
===================================================================
--- for-next.orig/lib/crc32.c
+++ for-next/lib/crc32.c
@@ -47,25 +47,29 @@ MODULE_LICENSE("GPL");

#if CRC_LE_BITS > 8 || CRC_BE_BITS > 8

+/* implements slicing-by-4 or slicing-by-8 algorithm */
static inline u32
-crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
+crc32_body(u32 crc, unsigned char const *buf, size_t len,
+ const u32 (*tab)[256], const unsigned bits)
{
# ifdef __LITTLE_ENDIAN
# define DO_CRC(x) (crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8))
-# define DO_CRC4 crc = t3[(crc) & 255] ^ \
- t2[(crc >> 8) & 255] ^ \
- t1[(crc >> 16) & 255] ^ \
- t0[(crc >> 24) & 255]
+# define DO_CRC4 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
+ t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
+# define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
+ t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])
# else
# define DO_CRC(x) (crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8))
-# define DO_CRC4 crc = t0[(crc) & 255] ^ \
- t1[(crc >> 8) & 255] ^ \
- t2[(crc >> 16) & 255] ^ \
- t3[(crc >> 24) & 255]
+# define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
+ t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
+# define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
+ t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])
# endif
const u32 *b;
- size_t rem_len;
+ size_t rem_len;
const u32 *t0 = tab[0], *t1 = tab[1], *t2 = tab[2], *t3 = tab[3];
+ const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];
+ u32 q;

/* Align it */
if (unlikely((long)buf & 3 && len)) {
@@ -73,13 +77,25 @@ crc32_body(u32 crc, unsigned char const
DO_CRC(*buf++);
} while ((--len) && ((long)buf)&3);
}
- rem_len = len & 3;
- /* load data 32 bits wide, xor data 32 bits wide. */
- len = len >> 2;
+
+ if (bits == 32) {
+ rem_len = len & 3;
+ len = len >> 2;
+ } else {
+ rem_len = len & 7;
+ len = len >> 3;
+ }
+
b = (const u32 *)buf;
for (--b; len; --len) {
- crc ^= *++b; /* use pre increment for speed */
- DO_CRC4;
+ q = crc ^ *++b; /* use pre increment for speed */
+ if (bits == 32)
+ crc = DO_CRC4;
+ else {
+ crc = DO_CRC8;
+ q = *++b;
+ crc ^= DO_CRC4;
+ }
}
len = rem_len;
/* And the last few bytes */
@@ -92,6 +108,7 @@ crc32_body(u32 crc, unsigned char const
return crc;
#undef DO_CRC
#undef DO_CRC4
+#undef DO_CRC8
}
#endif

@@ -135,7 +152,7 @@ u32 __pure crc32_le(u32 crc, unsigned ch
const u32 (*tab)[] = crc32table_le;

crc = (__force u32) __cpu_to_le32(crc);
- crc = crc32_body(crc, p, len, tab);
+ crc = crc32_body(crc, p, len, tab, CRC_LE_BITS);
crc = __le32_to_cpu((__force __le32)crc);
#endif
return crc;
@@ -183,7 +200,7 @@ u32 __pure crc32_be(u32 crc, unsigned ch
const u32 (*tab)[] = crc32table_be;

crc = (__force u32) __cpu_to_be32(crc);
- crc = crc32_body(crc, p, len, tab);
+ crc = crc32_body(crc, p, len, tab, CRC_BE_BITS);
crc = __be32_to_cpu((__force __be32)crc);
# endif
return crc;
Index: for-next/lib/crc32defs.h
===================================================================
--- for-next.orig/lib/crc32defs.h
+++ for-next/lib/crc32defs.h
@@ -6,29 +6,42 @@
#define CRCPOLY_LE 0xedb88320
#define CRCPOLY_BE 0x04c11db7

-/* How many bits at a time to use. Valid values are 1, 2, 4, 8, and 32. */
-/* For less performance-sensitive, use 4 or 8 */
+/*
+ * How many bits at a time to use. Valid values are 1, 2, 4, 8, 32 and 64.
+ * For less performance-sensitive, use 4 or 8 to save table size.
+ * For larger systems choose same as CPU architecture as default.
+ * This works well on X86_64, SPARC64 systems. This may require some
+ * elaboration after experiments with other architectures.
+ */
#ifndef CRC_LE_BITS
-# define CRC_LE_BITS 32
+# ifdef CONFIG_64BIT
+# define CRC_LE_BITS 64
+# else
+# define CRC_LE_BITS 32
+# endif
#endif
#ifndef CRC_BE_BITS
-# define CRC_BE_BITS 32
+# ifdef CONFIG_64BIT
+# define CRC_BE_BITS 64
+# else
+# define CRC_BE_BITS 32
+# endif
#endif

/*
* Little-endian CRC computation. Used with serial bit streams sent
* lsbit-first. Be sure to use cpu_to_le32() to append the computed CRC.
*/
-#if CRC_LE_BITS > 32 || CRC_LE_BITS < 1 || CRC_LE_BITS == 16 || \
+#if CRC_LE_BITS > 64 || CRC_LE_BITS < 1 || CRC_LE_BITS == 16 || \
CRC_LE_BITS & CRC_LE_BITS-1
-# error "CRC_LE_BITS must be one of {1, 2, 4, 8, 32}"
+# error "CRC_LE_BITS must be one of {1, 2, 4, 8, 32, 64}"
#endif

/*
* Big-endian CRC computation. Used with serial bit streams sent
* msbit-first. Be sure to use cpu_to_be32() to append the computed CRC.
*/
-#if CRC_BE_BITS > 32 || CRC_BE_BITS < 1 || CRC_BE_BITS == 16 || \
+#if CRC_BE_BITS > 64 || CRC_BE_BITS < 1 || CRC_BE_BITS == 16 || \
CRC_BE_BITS & CRC_BE_BITS-1
-# error "CRC_BE_BITS must be one of {1, 2, 4, 8, 32}"
+# error "CRC_BE_BITS must be one of {1, 2, 4, 8, 32, 64}"
#endif
Index: for-next/lib/gen_crc32table.c
===================================================================
--- for-next.orig/lib/gen_crc32table.c
+++ for-next/lib/gen_crc32table.c
@@ -1,23 +1,28 @@
#include <stdio.h>
+#include "../include/generated/autoconf.h"
#include "crc32defs.h"
#include <inttypes.h>

#define ENTRIES_PER_LINE 4

-#if CRC_LE_BITS <= 8
-#define LE_TABLE_SIZE (1 << CRC_LE_BITS)
+#if CRC_LE_BITS > 8
+# define LE_TABLE_ROWS (CRC_LE_BITS/8)
+# define LE_TABLE_SIZE 256
#else
-#define LE_TABLE_SIZE 256
+# define LE_TABLE_ROWS 1
+# define LE_TABLE_SIZE (1 << CRC_LE_BITS)
#endif

-#if CRC_BE_BITS <= 8
-#define BE_TABLE_SIZE (1 << CRC_BE_BITS)
+#if CRC_BE_BITS > 8
+# define BE_TABLE_ROWS (CRC_BE_BITS/8)
+# define BE_TABLE_SIZE 256
#else
-#define BE_TABLE_SIZE 256
+# define BE_TABLE_ROWS 1
+# define BE_TABLE_SIZE (1 << CRC_BE_BITS)
#endif

-static uint32_t crc32table_le[4][256];
-static uint32_t crc32table_be[4][256];
+static uint32_t crc32table_le[LE_TABLE_ROWS][256];
+static uint32_t crc32table_be[BE_TABLE_ROWS][256];

/**
* crc32init_le() - allocate and initialize LE table data
@@ -40,7 +45,7 @@ static void crc32init_le(void)
}
for (i = 0; i < LE_TABLE_SIZE; i++) {
crc = crc32table_le[0][i];
- for (j = 1; j < 4; j++) {
+ for (j = 1; j < LE_TABLE_ROWS; j++) {
crc = crc32table_le[0][crc & 0xff] ^ (crc >> 8);
crc32table_le[j][i] = crc;
}
@@ -64,18 +69,18 @@ static void crc32init_be(void)
}
for (i = 0; i < BE_TABLE_SIZE; i++) {
crc = crc32table_be[0][i];
- for (j = 1; j < 4; j++) {
+ for (j = 1; j < BE_TABLE_ROWS; j++) {
crc = crc32table_be[0][(crc >> 24) & 0xff] ^ (crc << 8);
crc32table_be[j][i] = crc;
}
}
}

-static void output_table(uint32_t (*table)[256], int len, char *trans)
+static void output_table(uint32_t (*table)[256], int rows, int len, char *trans)
{
int i, j;

- for (j = 0 ; j < 4; j++) {
+ for (j = 0 ; j < rows; j++) {
printf("{");
for (i = 0; i < len - 1; i++) {
if (i % ENTRIES_PER_LINE == 0)
@@ -92,15 +97,21 @@ int main(int argc, char** argv)

if (CRC_LE_BITS > 1) {
crc32init_le();
- printf("static const u32 crc32table_le[4][256] = {");
- output_table(crc32table_le, LE_TABLE_SIZE, "tole");
+ printf("static const u32 __cacheline_aligned "
+ "crc32table_le[%d][%d] = {",
+ LE_TABLE_ROWS, LE_TABLE_SIZE);
+ output_table(crc32table_le, LE_TABLE_ROWS,
+ LE_TABLE_SIZE, "tole");
printf("};\n");
}

if (CRC_BE_BITS > 1) {
crc32init_be();
- printf("static const u32 crc32table_be[4][256] = {");
- output_table(crc32table_be, BE_TABLE_SIZE, "tobe");
+ printf("static const u32 __cacheline_aligned "
+ "crc32table_be[%d][%d] = {",
+ BE_TABLE_ROWS, BE_TABLE_SIZE);
+ output_table(crc32table_be, LE_TABLE_ROWS,
+ BE_TABLE_SIZE, "tobe");
printf("};\n");
}