Abs

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3 total messages Started by Dennis Mon, 02 Sep 2002 08:15

#342

Author: Dennis
Date: Mon, 02 Sep 2002 08:15

7 lines
1054 bytes

Hi

How do i find the absolute value of an signed integer the fastest way?

8 bit, 16 bit & 32 bit integers.

Dennis

Re: Abs

#343

Author: Guido Gybels
Date: Mon, 02 Sep 2002 09:22

21 lines
1565 bytes

"Dennis" <marianndennis@email.dk> wrote in message
news:3D731E35.519D3AF5@email.dk...
> How do i find the absolute value of an signed integer the fastest way?

Use Pascal. Abs is not a real function and the compiler will generate the
appropriate code inline. That will always be faster than any call to a
separate assembly function. Besides there is not much to be optimised about
something like:

cdq
xor eax,{some register}
sub eax,{same register}

Guido


--
Guido Gybels
http://www.optimalcode.com/Guido
(Disclaimer: all remarks made apply to Intel processors unless specified
otherwise)

Re: Abs

#364

Author: Pierre Maurette
Date: Tue, 03 Sep 2002 03:32

28 lines
1430 bytes

"Guido Gybels" <guido.gybels@rnid.org.uk> a �crit dans le message de news:
3d732d53@newsgroups.borland.com...
> "Dennis" <marianndennis@email.dk> wrote in message
> news:3D731E35.519D3AF5@email.dk...
> cdq
> xor eax,{some register}
> sub eax,{same register}
>
32:
[{some register} is edx]
cdq
xor eax, edx
sub eax, edx

16:
cwd
xor  ax, dx
sub  ax, dx

8:
cbw
xor al, ah
sub al, ah

[Search for Q31810 in Microsoft's knowledge base]

Pierre

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