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Message-ID: <OFBF50514E.82734B36-ONC12578E7.005E58EE-C12578E7.005F648F@transmode.se>
Date: Tue, 9 Aug 2011 19:21:56 +0200
From: Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To: Bob Pearson <rpearson@...temfabricworks.com>
Cc: akpm@...ux-foundation.org, fzago@...temfabricworks.com,
linux@...izon.com, linux-kernel@...r.kernel.org
Subject: Re: [patch v3 6/7] crc32: add-slicing-by-8.diff
Bob Pearson <rpearson@...temfabricworks.com> wrote on 2011/08/09 07:27:59:
>
> add slicing-by-8 algorithm to the existing
> slicing-by-4 algorithm. This consists of:
>
> - extend largest BITS size from 32 to 64
> - extend table from tab[4][256] to tab[8][256]
> - change algorithm to align on 8 byte boundary
> (it was noted that all that is really required
> is that the inner loop must comsume 8 bytes.
> As written it can start on even or odd 4 byte
> boundary.)
So why not do that in the code too?
> - Add code for inner loop.
>
> Signed-off-by: Bob Pearson <rpearson@...temfabricworks.com>
>
> ---
> lib/crc32.c | 58 ++++++++++++++++++++++++++++++++++++++++++---------
> lib/crc32defs.h | 14 ++++++------
> lib/gen_crc32table.c | 40 +++++++++++++++++++++--------------
> 3 files changed, 79 insertions(+), 33 deletions(-)
>
> Index: infiniband/lib/crc32.c
> ===================================================================
> --- infiniband.orig/lib/crc32.c
> +++ infiniband/lib/crc32.c
> @@ -45,6 +45,7 @@ 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])
> {
> @@ -54,41 +55,78 @@ crc32_body(u32 crc, unsigned char const
> tab[2][(crc >> 8) & 255] ^ \
> tab[1][(crc >> 16) & 255] ^ \
> tab[0][(crc >> 24) & 255]
> +# define DO_CRC8a (tab[7][(q) & 255] ^ \
> + tab[6][(q >> 8) & 255] ^ \
> + tab[5][(q >> 16) & 255] ^ \
> + tab[4][(q >> 24) & 255])
> +# define DO_CRC8b (tab[3][(q) & 255] ^ \
> + tab[2][(q >> 8) & 255] ^ \
> + tab[1][(q >> 16) & 255] ^ \
> + tab[0][(q >> 24) & 255])
> # else
> # 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]
> +# define DO_CRC8a (tab[4][(q) & 255] ^ \
> + tab[5][(q >> 8) & 255] ^ \
> + tab[6][(q >> 16) & 255] ^ \
> + tab[8][(q >> 24) & 255])
> +# define DO_CRC8b (tab[0][(q) & 255] ^ \
> + tab[1][(q >> 8) & 255] ^ \
> + tab[2][(q >> 16) & 255] ^ \
> + tab[3][(q >> 24) & 255])
> # endif
> const u32 *b;
> - size_t rem_len;
> + size_t init_len;
> + size_t middle_len;
> + size_t rem_len;
> +
> + /* break buf into init_len bytes before and
> + * rem_len bytes after a middle section with
> + * middle_len properly aligned words */
> +# if CRC_LE_BITS == 32
> + init_len = min((-((uintptr_t)buf)) & 3, len);
> + middle_len = (len - init_len) >> 2;
> + rem_len = (len - init_len) & 3;
> +# else
> + init_len = min((-((uintptr_t)buf)) & 7, len);
> + middle_len = (len - init_len) >> 3;
> + rem_len = (len - init_len) & 7;
> +# endif
>
> /* Align it */
> - if (unlikely((long)buf & 3 && len)) {
> + if (unlikely(init_len)) {
> do {
> DO_CRC(*buf++);
> - } while ((--len) && ((long)buf)&3);
> + } while (--init_len);
> }
As discussed earlier, don't change initial loop. Best left alone unless
you have verified it generates better code.
> - rem_len = len & 3;
> - /* load data 32 bits wide, xor data 32 bits wide. */
> - len = len >> 2;
> b = (const u32 *)buf;
> - for (--b; len; --len) {
> + for (--b; middle_len; --middle_len) {
> +# if CRC_LE_BITS == 32
> crc ^= *++b; /* use pre increment for speed */
> DO_CRC4;
> +# else
> + u32 q;
> + q = crc ^ *++b;
> + crc = DO_CRC8a;
> + q = *++b;
> + crc ^= DO_CRC8b;
> +# endif
> }
> - len = rem_len;
> /* And the last few bytes */
> - if (len) {
> + if (rem_len) {
> u8 *p = (u8 *)(b + 1) - 1;
> do {
> DO_CRC(*++p); /* use pre increment for speed */
> - } while (--len);
> + } while (--rem_len);
> }
> return crc;
> #undef DO_CRC
> #undef DO_CRC4
> +#undef DO_CRC8a
> +#undef DO_CRC8b
> }
> #endif
>
> Index: infiniband/lib/crc32defs.h
> ===================================================================
> --- infiniband.orig/lib/crc32defs.h
> +++ infiniband/lib/crc32defs.h
> @@ -6,29 +6,29 @@
> #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. */
> +/* 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 */
> #ifndef CRC_LE_BITS
> -# define CRC_LE_BITS 32
> +# define CRC_LE_BITS 64
64 bits as default for all archs? Not very likely, especially
as I already told you that 64 bits made my ppc32 drop to
half the size.
> #endif
> #ifndef CRC_BE_BITS
> -# define CRC_BE_BITS 32
> +# define CRC_BE_BITS 64
> #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, 64}"
32 is missing
> #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, 64}"
Ditto.
> #endif
> Index: infiniband/lib/gen_crc32table.c
> ===================================================================
> --- infiniband.orig/lib/gen_crc32table.c
> +++ infiniband/lib/gen_crc32table.c
> @@ -4,20 +4,24 @@
>
> #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[8][256];
> -static uint32_t crc32table_be[8][256];
> +static uint32_t crc32table_le[LE_TABLE_ROWS][256];
> +static uint32_t crc32table_be[BE_TABLE_ROWS][256];
256 should be XX_TABLE_SIZE
>
> /**
> * crc32init_le() - allocate and initialize LE table data
> @@ -40,7 +44,7 @@ static void crc32init_le(void)
> }
> for (i = 0; i < LE_TABLE_SIZE; i++) {
> crc = crc32table_le[0][i];
> - for (j = 1; j < 8; j++) {
> + for (j = 1; j < LE_TABLE_ROWS; j++) {
> crc = crc32table_le[0][crc & 0xff] ^ (crc >> 8);
> crc32table_le[j][i] = crc;
> }
> @@ -64,18 +68,18 @@ static void crc32init_be(void)
> }
> for (i = 0; i < BE_TABLE_SIZE; i++) {
> crc = crc32table_be[0][i];
> - for (j = 1; j < 8; 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[8][256], int len, char *trans)
> +static void output_table(uint32_t (*table)[256], int rows, int len, char *trans)
Size is not always 256.
> {
> int i, j;
>
> - for (j = 0 ; j < 8; j++) {
> + for (j = 0 ; j < rows; j++) {
> printf("{");
> for (i = 0; i < len - 1; i++) {
> if (i % ENTRIES_PER_LINE == 0)
> @@ -92,15 +96,19 @@ int main(int argc, char** argv)
>
> if (CRC_LE_BITS > 1) {
> crc32init_le();
> - printf("static const u32 crc32table_le[8][256] = {");
> - output_table(crc32table_le, LE_TABLE_SIZE, "tole");
> + printf("static const u32 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[8][256] = {");
> - output_table(crc32table_be, BE_TABLE_SIZE, "tobe");
> + printf("static const u32 crc32table_be[%d][%d] = {",
> + BE_TABLE_ROWS, BE_TABLE_SIZE);
> + output_table(crc32table_be, LE_TABLE_ROWS,
> + BE_TABLE_SIZE, "tobe");
> printf("};\n");
> }
>
--
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