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Bug #2824

closed

New higher speed CRC code

Added by robin.carey1 over 9 years ago. Updated over 9 years ago.

Status:
Rejected
Priority:
Normal
Assignee:
-
Category:
-
Target version:
-
Start date:
06/09/2015
Due date:
% Done:

0%

Estimated time:

Description

Dear DragonFlyBSD bugs,

This isn't really a bug. I noticed there is the possibility of improving
the performance of the recently committed new CRC code ("fast iscsi crc
code").

In the following function:

sys/libkern/icrc32.c
<http://gitweb.dragonflybsd.org/dragonfly.git/blob/d557434b1f5510b6fed895379af444f0d034c07b:/sys/libkern/icrc32.c>

static uint32_t
singletable_crc32c(uint32_t crc, const void *buf, size_t size) {
const uint8_t *p = buf;

while (size--)
               crc = crc32Table[(crc ^ *p++) & 0xff] ^ (crc >> 8);
return crc;
}

The two separate operations of "size--" and "*p++" could be combined into
one operation. The way that I would do that would be something like:

...
size_t I;
for (i = 0; i < size; ++i) {
crc = crc32Table[(crc ^ p[i]) & 0xff] ^ (crc >> 8);
}
...

So you would be saving one operation; performance improvement.

I haven't looked at the rest of the code, so perhaps there are other
performance improvements that could be had.

Hope this helps ...

--
Sincerely,

Robin Carey BSc

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