Re: Multiply Overflow - when to use UMULH
Uncle George (firstname.lastname@example.org)
Sun, 24 Nov 1996 07:51:07 -0500
Uncle George wrote:
I try to mult two (possibly) 48 bit integers. Sometimes these nums will
overflow the 64 bit reg. I'd like to know if there is an easy way
to get at the overflow bit.
>From reading the asm manual, you have to wait for the pipeline to
clear, cause an exception, then get the status/overflow bit.
1) whis is faster ?
umul, then umulh ( forget the exception fault )
2) a) umul ( no exception to process )
b) umul -> exception -> do umulh ( only when truely needed )
I have no timeings for instruction sets. I have no timeings for
I'd really like to test an overflow bit that did not involve an
exception, but that does not seem to be the case with alpha's ( maybe
all risc's )
To unsubscribe: send e-mail to email@example.com with
'unsubscribe' as the subject. Do not send it to firstname.lastname@example.org
Product Errata |
About Us |
Linux Info |
No Frames |
Copyright © 1995-1997 Red Hat Software. Legal notices