Bitwise negation Post: 302117669

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Top Forums Shell Programming and Scripting Bitwise negation Post 302117669 by Perderabo on Wednesday 16th of May 2007 12:19:11 AM

05-16-2007

Administrator Emeritus

If the course says that ((~ 2#1001)) evaluates to 2#110, I wonder what shell they were using. With ksh I get:
$ typeset -i2 b
$ echo $((2#1001)) $((b=~2#1001)) $b
9 -10 -2#1010

With bash, there is no -i2 and I don't see an easy way to get binary output. I could code my own routine, but then the behavior would be whatever I decided. (But I get the "9 -10" part with bash.) Since ksh alone has a way to output binary, I did a few experiments with it. A negative number has many leading 1's while a non-negative has many leading zeros. ksh uses enough positions to output the the leftmost bit transistion. If you exceed the shell's integer size, you get undefined results, but clamping at positive or negative "infinity" (max/min integer) is common with both ksh and bash. The shells I checked have either 32 or 64 bit integers.

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LEARN ABOUT SUNOS

shells

shells(4)							   File Formats 							 shells(4)

NAME

       shells - shell database

SYNOPSIS

       /etc/shells

DESCRIPTION

       The shells file contains a list of the shells on the system. Applications use this file to determine whether a shell is valid. See getuser-
       shell(3C). For each shell a single line should be present, consisting of the shell's path, relative to root.

       A hash mark (#) indicates the beginning of a comment; subsequent characters up to the end of the line are not interpreted by  the  routines
       which search the file. Blank lines are also ignored.

       The  following  default	shells are used by utilities: /bin/bash, /bin/csh, /bin/jsh, /bin/ksh, /bin/pfcsh, /bin/pfksh, /bin/pfsh, /bin/sh,
       /bin/tcsh,  /bin/zsh,  /sbin/jsh,  /sbin/sh,  /usr/bin/bash,  /usr/bin/csh,  /usr/bin/jsh,  /usr/bin/ksh,  /usr/bin/pfcsh,  /usr/bin/pfksh,
       /usr/bin/pfsh, and /usr/bin/sh, /usr/bin/tcsh, /usr/bin/zsh. Note that /etc/shells overrides the default list.

       Invalid shells in /etc/shells may cause unexpected behavior (such as being unable to log in by way of ftp(1)).

FILES

       /etc/shells	       lists shells on system

SEE ALSO

       vipw(1B), ftpd(1M), sendmail(1M), getusershell(3C), aliases(4)

SunOS 5.10							    4 Jun 2001								 shells(4)