From: "Tony Harminc" <[email protected]>
Sent: Tuesday, June 03, 2014 11:52 AM
On 2 June 2014 20:14, Robin Vowels <[email protected]> wrote:
From: "Rob van der Heij" <[email protected]>
Sent: Tuesday, June 03, 2014 1:00 AM
More recently I've been working on porting Linux gcc object code to CMS,
and now that I needed a nice checksum routine, I figured I might take a
popular open source checksum routine http://en.wikipedia.org/wiki/Adler-32
and let gcc compile and optimize it. Since the generated assembler source
wasn't that obvious to me, I was getting interested to know why.
My simplistic implementation was like this (for each byte, so wrapped in a
loop)
* IC R4,0(R6) AR R2,R4 AR R3,R2 *
Must have muissed something here.
A 3-instruction loop to sum bytes.
LA 6,X+offset (last byte of area to be summed)
SR 2,2
SR 4,4
Loop IC 4,0(0,6)
AR 2,4
BCT 6,Loop
And you can use BCTR to save a few µS.
Why do you think BCTR would save such a large amount of time?
And while I have the manual out, BCTR is from 40% to 70% faster than BCT.
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