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Rotate-byte instructions

General and Gameplay Programming Programming

Started by ZackCQB February 28, 2004 06:56 PM

6 comments, last by ZackCQB 20 years, 2 months ago

ZackCQB

122

Author

February 28, 2004 06:56 PM

Is there any Rotate-bit instructions in C/C++? I mean the C/C++ equivalents of Assembly''s ROL and ROR instructions. Or am I stuck using embedded ASM?

http://thegeekery.org/

Fruny

1,658

February 28, 2004 07:25 PM

There isn''t.

“Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.” — Brian W. Kernighan (C programming language co-inventor)

"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan

krez

443

February 28, 2004 07:32 PM

it wouldn''t be hard to whip something up, but if you know how the ASM will be better anyway.

--- krez ([email="krez_AT_optonline_DOT_net"]krez_AT_optonline_DOT_net[/email])

ZackCQB

122

Author

February 28, 2004 09:52 PM

Yeah, I''m okay at ASM, so I guess I''ll do it that way.
Thanks.

http://thegeekery.org/

SiCrane

11,840

February 28, 2004 10:42 PM

Some compilers supply functions to do it. For example, MSVC uses the _rotl() and _rotr() functions. And because of the magic of compiler intrisics they turn into ROL and ROR assembly instructions when compiled in release mode.

ZackCQB

122

Author

February 29, 2004 08:55 PM

I''m stuck with Mingw32, but hopefully I''ll get MSVC sometime.

http://thegeekery.org/

SiCrane

11,840

March 01, 2004 03:14 AM

The good news is that MinGW, because it uses the Microsoft C runtime, has the _rotl() and _rotr() functions. So you can use them without resorting to inline assembly.

The bad news is that, even with optimization, MinGW doesn''t recognize _rotl() or _rotr() as intrinsics so they''ll show up in the machine code as function calls. (At least of MinGW 3.2 20020817-1, I haven''t upgraded my non-cygwin gcc builds on my system in a while.)