Messages in this thread Patches in this message | ![/](/images/icornerl.gif) | | Date | Tue, 18 Feb 2003 10:28:57 +0100 | From | Joakim Tjernlund <> | Subject | [PATCH] crc32 improvements for 2.5, more optimizations |
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Hi
Here is another update(against BK curr) for crc32(). A kind soul pointed out the optimizations below.
lib/crc32defs.h: - Make it possible to define new values for CRC_LE_BITS/CRC_BE_BITS without modifying the source.
lib/crc32.c: - Eliminate the need for ENDIAN_SHIFT. Saves a 24 bit shift in the byte loops.
- Swap the XOR expression in DO_CRC. gcc for x86 can not do that simple optimization itself(gcc 3.2.2 and RH gcc 2.96 tested). Will improve performance with 20-25% on x86.
Joakim Tjernlund
--- lib/crc32defs.h Wed Jan 8 01:35:35 2003 +++ lib/new.crc32defs.h Tue Feb 18 09:38:08 2003 @@ -8,8 +8,12 @@ /* How many bits at a time to use. Requires a table of 4<<CRC_xx_BITS bytes. */ /* For less performance-sensitive, use 4 */ -#define CRC_LE_BITS 8 -#define CRC_BE_BITS 8 +#ifndef CRC_LE_BITS +# define CRC_LE_BITS 8 +#endif +#ifndef CRC_BE_BITS +# define CRC_BE_BITS 8 +#endif /* * Little-endian CRC computation. Used with serial bit streams sent
--- lib/crc32.c Tue Feb 18 09:29:46 2003 +++ lib/new.crc32.c Tue Feb 18 09:43:15 2003 @@ -90,19 +90,16 @@ const u32 *tab = crc32table_le; # ifdef __LITTLE_ENDIAN -# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ] -# define ENDIAN_SHIFT 0 +# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8) # else -# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ] -# define ENDIAN_SHIFT 24 +# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8) # endif crc = __cpu_to_le32(crc); /* Align it */ if(unlikely(((long)b)&3 && len)){ do { - crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; - DO_CRC; + DO_CRC(*((u8 *)b)++); } while ((--len) && ((long)b)&3 ); } if(likely(len >= 4)){ @@ -112,10 +109,10 @@ --b; /* use pre increment below(*++b) for speed */ do { crc ^= *++b; - DO_CRC; - DO_CRC; - DO_CRC; - DO_CRC; + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); } while (--len); b++; /* point to next byte(s) */ len = save_len; @@ -123,8 +120,7 @@ /* And the last few bytes */ if(len){ do { - crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; - DO_CRC; + DO_CRC(*((u8 *)b)++); } while (--len); } @@ -195,19 +191,16 @@ const u32 *tab = crc32table_be; # ifdef __LITTLE_ENDIAN -# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ] -# define ENDIAN_SHIFT 24 +# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8) # else -# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ] -# define ENDIAN_SHIFT 0 +# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8) # endif crc = __cpu_to_be32(crc); /* Align it */ if(unlikely(((long)b)&3 && len)){ do { - crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; - DO_CRC; + DO_CRC(*((u8 *)b)++); } while ((--len) && ((long)b)&3 ); } if(likely(len >= 4)){ @@ -217,10 +210,10 @@ --b; /* use pre increment below(*++b) for speed */ do { crc ^= *++b; - DO_CRC; - DO_CRC; - DO_CRC; - DO_CRC; + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); } while (--len); b++; /* point to next byte(s) */ len = save_len; @@ -228,8 +221,7 @@ /* And the last few bytes */ if(len){ do { - crc ^= *((u8 *)b)++ << ENDIAN_SHIFT; - DO_CRC; + DO_CRC(*((u8 *)b)++); } while (--len); } return __be32_to_cpu(crc);
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