Messages in this thread Patch in this message | | | Date | Thu, 13 Feb 2003 12:13:16 +0100 | From | Joakim Tjernlund <> | Subject | [PATCH] crc32 improvements for 2.5 [RESEND] |
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[This is a resend, feedback welcome]
Hi
I did the optimizations in the crc32 patch Brian Murphy submitted a while ago. Now I have cleaned it up a little and made some more optimizations.
gcc is quite bad at loop optimizations (at least for PPC) so I have rewritten them to make gcc to generate better code. Even recent gcc's(3.2.x) produces better code.
Also reduced the unrolling since it did not make a noticeable difference.
Joakim Tjernlund
--- lib/crc32.c.org Thu Jan 9 00:19:02 2003 +++ lib/crc32.c Tue Feb 4 19:05:01 2003 @@ -87,55 +87,51 @@ { # if CRC_LE_BITS == 8 const u32 *b =(u32 *)p; - const u32 *e; - /* load data 32 bits wide, xor data 32 bits wide. */ + const u32 *tab = crc32table_le; - crc = __cpu_to_le32(crc); - /* Align it */ - for ( ; ((long)b)&3 && len ; len--){ -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_le[ (crc ^ *((u8 *)b)++) & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_le[ crc>>24 ^ *((u8 *)b)++ ]; -# endif - } - e = (u32 *) ( (u8 *)b + (len & ~7)); - while (b < e) { - crc ^= *b++; -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; -# endif - crc ^= *b++; # ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_le[ crc & 0xff ]; +# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ] +# define ENDIAN_SHIFT 0 # else - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_le[ crc >> 24 ]; +# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ] +# define ENDIAN_SHIFT 24 # endif + + crc = __cpu_to_le32(crc); + /* Align it */ + if(unlikely(((long)b)&3 && len)){ + do { + crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; + DO_CRC; + } while ((--len) && ((long)b)&3 ); + } + if(likely(len >= 4)){ + /* load data 32 bits wide, xor data 32 bits wide. */ + size_t save_len = len & 3; + len = len >> 2; + --b; /* use pre increment below(*++b) for speed */ + do { + crc ^= *++b; + DO_CRC; + DO_CRC; + DO_CRC; + DO_CRC; + } while (--len); + b++; /* point to next byte(s) */ + len = save_len; } /* And the last few bytes */ - e = (u32 *)((u8 *)b + (len & 7)); - while (b < e){ -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_le[ (crc ^ *((u8 *)b)++) & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_le[ crc>>24 ^ *((u8 *)b)++ ]; -# endif + if(len){ + do { + crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; + DO_CRC; + } while (--len); } - return __le32_to_cpu(crc) ; + + return __le32_to_cpu(crc); +#undef ENDIAN_SHIFT +#undef DO_CRC + # elif CRC_LE_BITS == 4 while (len--) { crc ^= *p++; @@ -196,55 +192,50 @@ { # if CRC_BE_BITS == 8 const u32 *b =(u32 *)p; - const u32 *e; - /* load data 32 bits wide, xor data 32 bits wide. */ + const u32 *tab = crc32table_be; - crc = __cpu_to_be32(crc); - /* Align it */ - for ( ; ((long)b)&3 && len ; len--){ -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_be[ (crc ^ *((u8 *)b)++) & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_be[ crc>>24 ^ *((u8 *)b)++ ]; -# endif - } - e = (u32 *) ( (u8 *)b + (len & ~7)); - while (b < e) { - crc ^= *b++; -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; -# endif - crc ^= *b++; # ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; - crc = (crc>>8) ^ crc32table_be[ crc & 0xff ]; +# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ] +# define ENDIAN_SHIFT 24 # else - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; - crc = (crc<<8) ^ crc32table_be[ crc >> 24 ]; +# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ] +# define ENDIAN_SHIFT 0 # endif + + crc = __cpu_to_be32(crc); + /* Align it */ + if(unlikely(((long)b)&3 && len)){ + do { + crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; + DO_CRC; + } while ((--len) && ((long)b)&3 ); + } + if(likely(len >= 4)){ + /* load data 32 bits wide, xor data 32 bits wide. */ + size_t save_len = len & 3; + len = len >> 2; + --b; /* use pre increment below(*++b) for speed */ + do { + crc ^= *++b; + DO_CRC; + DO_CRC; + DO_CRC; + DO_CRC; + } while (--len); + b++; /* point to next byte(s) */ + len = save_len; } /* And the last few bytes */ - e = (u32 *)((u8 *)b + (len & 7)); - while (b < e){ -# ifdef __LITTLE_ENDIAN - crc = (crc>>8) ^ crc32table_be[ (crc ^ *((u8 *)b)++) & 0xff ]; -# else - crc = (crc<<8) ^ crc32table_be[ crc>>24 ^ *((u8 *)b)++ ]; -# endif - } - return __be32_to_cpu(crc) ; + if(len){ + do { + crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; + DO_CRC; + } while (--len); + } + return __be32_to_cpu(crc); +#undef ENDIAN_SHIFT +#undef DO_CRC + # elif CRC_BE_BITS == 4 while (len--) { crc ^= *p++ << 24;
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