Hi Prafulla, Le 05/10/2010 07:57, Prafulla Wadaskar a écrit : > > >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Albert Aribaud >> Sent: Tuesday, October 05, 2010 3:52 AM >> To: [email protected] >> Subject: [U-Boot] [PATCH] orion5x: optimize window size computation >> >> >> Signed-off-by: Chris Moore<[email protected]> >> --- >> >> This is a simple optimization of the orion5x window size >> computation. This code was contributed by Chris Moore so >> I put his Signed-off-by rather than mine. > This is wrong, you should be singed-off since you are posting and Chris can > be contributor > Or let him post the patch. >
I asked Albert to post the patch as I am mainly a U-Boot lurker and I have no U-Boot git tree. If there is a problem I don't mind if he signs off either with or without me. >> See<http://www.mail-archive.com/[email protected]/msg37075.html> >> >> arch/arm/cpu/arm926ejs/orion5x/cpu.c | 30 >> ++++++++++++++++++++---------- >> 1 files changed, 20 insertions(+), 10 deletions(-) >> >> diff --git a/arch/arm/cpu/arm926ejs/orion5x/cpu.c >> b/arch/arm/cpu/arm926ejs/orion5x/cpu.c >> index c36d7bf..5c443fe 100644 >> --- a/arch/arm/cpu/arm926ejs/orion5x/cpu.c >> +++ b/arch/arm/cpu/arm926ejs/orion5x/cpu.c >> @@ -48,24 +48,34 @@ void reset_cpu(unsigned long ignored) >> } >> >> /* >> - * Window Size >> + * Compute Window Size field value from size expressed in bytes >> * Used with the Base register to set the address window >> size and location. >> * Must be programmed from LSB to MSB as sequence of ones followed by >> * sequence of zeros. The number of ones specifies the size >> of the window in >> * 64 KByte granularity (e.g., a value of 0x00FF specifies >> 256 = 16 MByte). >> - * NOTE: A value of 0x0 specifies 64-KByte size. >> + * NOTES: >> + * 1) A sizeval equal to 0x0 specifies 4 TB. >> + * 2) A return value of 0x0 specifies 64 KB. >> */ >> unsigned int orion5x_winctrl_calcsize(unsigned int sizeval) >> { >> - int i; >> - unsigned int j = 0; >> - u32 val = sizeval>> 1; >> + /* >> + * Calculate the number of 64 KiB blocks needed minus >> one (rounding up). >> + * For sizeval> 0 this is equivalent to: >> + * sizeval = (u32) ceil((double) sizeval / 65536.0) - 1 >> + */ >> + sizeval = (sizeval - 1)>> 16; >> >> - for (i = 0; val>= 0x10000; i++) { >> - j |= (1<< i); >> - val = val>> 1; >> - } >> - return 0x0000ffff& j; >> + /* >> + * Propagate 'one' bits to the right by 'oring' them. >> + * We need only treat bits 15-0. >> + */ >> + sizeval |= sizeval>> 1; /* 'Or' bit 15 onto bit 14 */ >> + sizeval |= sizeval>> 2; /* 'Or' bits 15-14 onto bits 13-12 */ >> + sizeval |= sizeval>> 4; /* 'Or' bits 15-12 onto bits 11-8 */ >> + sizeval |= sizeval>> 8; /* 'Or' bits 15-8 onto bits 7-0*/ >> + >> + return sizeval; > BTW: How much this saves on size? > It is not so much a question of size. I am afraid that the other version was just plain *wrong* :( See my previous post here: http://www.mail-archive.com/[email protected]/msg36996.html In this post I presented two versions: a) a corrected version along the lines of the original, b) a version similar to the above. The loop version may be slightly shorter in code size, particularly if one removes the unnecessary and with 0x0000ffff at the end. But aesthetically I find the version above much more pleasing. (Didn't Donald Knuth write "The *Art* of Computer Programming"?) It is also much faster for large window sizes but this probably doesn't matter here. Cheers, Chris _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
