(c) 2000 M. A. Chatterjee, < deftio [at] deftio [dot] com >
release notes:
- cleaned up comments 2012
- changed to markdown 2016
Actually this code does .. virtually nothing and is more of a historical exploration of different compiler/processor issues I was investigating in the mid 1990s. Both embedded (e.g. ARM, mcore, 68xxx) and desktop (PowerPC, 80x86) compilers were being target for work I was doing in speech and handwriting recognition. Many of the embedded platforms were running in the low single digit to low 10s of MHz.
These musings on bit shifting and absolute values come from the mid 1990s when processors could have pipeline stalls and I was experimenting with ways to avoid cache/pipeline misses on branch predictors.
This started a subset line of thinking on measuring branch penalties vs statements. Some processors then didn't have hardware absolute value (ABS) instructions so with a little fun the macros below were created. I make no statements that they were useful and I looked at these and other statement constructs to study effects of branch-miss, cache fill issues for a specific problem I was dealing with at the time which which I've since forgotten.
Those of you coming from a Java background, bear in mind the difference in Java between >> and >>> as here in C >> means arithmetic shift (e.g. if there is a 1 in the high order bit then the register 1 fills not zero-fills).
I'm publishing this as a way to preserve some thought experiments rather than as a true open-source "library" of any kind. Many times I've run accross some little brainbender of code someone wrote and thought "hmmm cute" and soe here is a small contribution to such thinking.
Cheers- MC
See C language code "absolute_this.c" command line compile via gcc or equivalent. e.g. in gcc
#build it
gcc absolute_this.c -lm -o abs_this
#run it
./abs_this
Note the code uses stdio.h so your platform will need to support printf like
statements.
Copyright (c) 2001-2016, M. A. Chatterjee < deftio at deftio dot com > All rights reserved.
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