Re: 64-bit arithmetic in scripts?

From: Andrew (infofarmer_at_mail.ru)
Date: 10/01/04

  • Next message: Simon Barner: "Re: Last Question On Which Release Is Best For Production" 
    Date: Fri, 1 Oct 2004 12:56:14 +0400

    Dan Nelson has kindly explained everything:
    > In the last episode (Oct 01), Andrew said:
    > > Thanks! I haven't thought about using expr.
    > >
    > > How come that my expr(1) manpage has nothing to say about -e option?
    > > In fact my expr(1) does not accept it. I have FreeBSD 4.10. I've
    just
    > > looked into a current manpage from www.freebsd.org, and it says
    > > something about 4.x compatibility.
    > >
    > > What is the best way to go if I need to write scripts now, but I'm
    > > planning to switch to 5.x later? Can I upgrade expr(1) now? If not,
    > > what should I do?
    >
    > In 4.x, expr does 64-bit math by default. Apparently POSIX requires
    > that expr use whatever the systems' "signed long" size is, so the
    > default was changed for 5.x, and -e was added to get the old
    behaviour.
    >
    > If you want your script to work on both, you'll have to do a feature
    > test. I started out just testing expr and expr -e, but it sort of
    > grew... The following script will check the shell's math, two ways of
    > calling expr, and finally fall back on calling bc. As long as you
    just
    > use the basic math operators, quote your "*"'s, and put spaces between
    > everything, all the methods should be compatible, and your script will
    > work on any bourne-compatible shell :)
    >
    > #! /bin/sh
    >
    > if [ x$(( 65536 * 65536 )) = "x4294967296" ] ; then
    > shellarith() { echo $(( $@ )) ; }
    > MATH="shellarith"
    > else
    > if [ x`expr 65536 "*" 65536` = "x4294967296" ] ; then
    > MATH="expr"
    > else
    > if [ x`expr -e 65536 "*" 65536 2>/dev/null` = x"4294967296" ] ;
    then
    > MATH="expr -e"
    > else
    > if [ x`echo 65536 "*" 65536 | bc` = "x4294967296" ] ; then
    > bcfunc() { echo "$@" | bc ; }
    > MATH="bcfunc"
    > else
    > echo "Can't do 64-bit math noway nohow"
    > fi
    > fi
    > fi
    > fi
    >
    > echo "Using $MATH"
    > bigval=`$MATH 65536 "*" 65536`
    > echo $bigval

    Thank you very much! I think, I'll just assign MATH="expr" and change it
    to something else when I need it.

    Best regards,
    Andrew P.

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