Messages in this thread Patch in this message | | | Date | Tue, 20 May 2008 17:25:29 +0200 (CEST) | From | Soumyadip Das Mahapatra <> | Subject | Re: [PATCH 1/2] bitreversal program |
| |
Thanks for giving a reply Akinobu :-) I forgot that bitrev8() is static in header file. Sorry for that.
Below is my new patch considering this. Cant it be applicable? Please review it.
I know that my bitrev8() takes more instructions than that of yours. But we have to think about faster access of cpu cache over that of memory cache(which your bit_rev_table uses).
Thanks anyway ;-)
---Inline Attachment--- --- a/include/linux/bitrev.h 2008-04-17 08:19:44.000000000 +0530 +++ b/include/linux/bitrev.h 2008-05-20 20:41:13.000000000 +0530 @@ -3,11 +3,49 @@
#include <linux/types.h>
-extern u8 const byte_rev_table[256]; +/** + * Here is a generalised bit reversal program + * @x: word to get bits reversed + * @k: key, explained below + * for k = 31, it reverses the bits of word(32 bit) + * for k = 24, it reverses the bytes in word + * for k = 7, it reverses the bits in every byte without + * changing the positions of bytes in a word + * and for k = 16 it swaps the left and right halves of a + * word + */ + +static inline u32 gen_bit_rev(u32 x, u32 k) +{ + if(k & 1) + x = (x & 0x55555555) << 1 | (x & 0xaaaaaaaa) >> 1; + if(k & 2) + x = (x & 0x33333333) << 2 | (x & 0xcccccccc) >> 2; + if(k & 4) + x = (x & 0x0f0f0f0f) << 4 | (x & 0xf0f0f0f0) >> 4; + if(k & 8) + x = (x & 0x00ff00ff) << 8 | (x & 0xff00ff00) >> 8; + if(k & 16) + x = (x & 0x0000ffff) << 16 | (x & 0xffff0000) >> 16; + + return x; +} + +/** + * bitrev8(): function for reversing bits of a byte + * @byte: the byte to get its bits reversed + */
static inline u8 bitrev8(u8 byte) { - return byte_rev_table[byte]; + u8 k = 7; + if(k & 1) + byte = (byte & 0x5555) << 1 | (byte & 0xaaaa) >> 1; + if(k & 2) + byte = (byte & 0x3333) << 2 | (byte & 0xcccc) >> 2; + if(k & 4) + byte = (byte & 0x0f0f) << 4 | (byte & 0xf0f0) >> 4; + return byte; }
extern u32 bitrev32(u32 in);
-- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.
| |