Re: Portable bitwise operations library (was Re: Portability Considerations)

[Michael Riedl]

Hallo Alice,

just tried your code with XDS Modula-2 (single pass 32 Bit compiler).

For the implementation module of CardBitOps you need to shift the 
declaration of powerOf2 to the top of the module, otherwise a single 
pass compiler will claim about that.

For the test module you are using WriteString for some single char 
outputs - gives at least a warning (would replace by WriteChar) and the 
import of Bitwidth is unused (all more or less cosmetics ... ).

Finally, the "0 rotated left by 0" results in an exception (if all is 
compiled with bound checks enabled):

<snip>

0 shifted left by 0 is 0
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 -> 0000 : 0000 : 
0000 : 0000 : 0000 : 0000 : 0000 : 0000
0 shifted right by 0 is 0
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 -> 0000 : 0000 : 
0000 : 0000 : 0000 : 0000 : 0000 : 0000
0 shifted left with carry by 0 is 0
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 -> 0000 : 0000 : 
0000 : 0000 : 0000 : 0000 : 0000 : 0000
Carry: 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000
0 arithmetically shifted right by 0 is 0
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000 -> 0000 : 0000 : 
0000 : 0000 : 0000 : 0000 : 0000 : 0000
0 rotated left by 0 is
#RTS: unhandled exception #1: expression out of bounds at line 270 of 
CardBitOps.mod

Had a look in the code and replaced

-----

 IF n = 0 THEN

  (* NOP *)

ELSIF shiftFactor = 0 THEN

  (* NOP *)

-----

by

----

 IF (n = 0) OR (shiftFactor = 0) THEN

    (* NOP *)

----

in shl, shr, ashr. I also added

----

  IF (shiftFactor = 0) THEN
    (* NOP *)
    RETURN n
  ELSE

-----

in rotr, rotl and the tests passed. Attached the updated versions (the 
test module is renamed to not mix it up with your version) and the 
output of the updated portable code with the XDS compiler.

In the hope that this is helpful (and I did not spoile the code) ...

Gruß

Michael


Am 22.03.24 um 08:49 schrieb Alice Osako:
> Eric Streit:
> > Hi Alice,
> >
> > imho, I think this list is just perfect for the discussions about 
> > Modula2; Telegram Modula2 is not restricted by M2R10, we exchange 
> > about any Modula2 stuff (, and Oberon which is not very liked by 
> > Benjamin.)
>
> Fair enough then, I will continue posting here unless someone says to 
> stop.
>
> In the meanwhile, I have worked out most of a version of the bitwise 
> library for GNU Modula-2 on x86_64. I did use inline assembly 
> extensively, but if this is a problem I can easily re-write it as 
> stand-alone assembly functions.
>
> See https://github.com/Schol-R-LEA/Modula-2-Portable-Bit-Manipulation 
> for the current status of this project.

CardBitOps.mod
Description: audio/mod

TstCardBitOps.mod
Description: audio/mod

TestResults.xds
Description: Text document