pound

来自「Calc Software Package for Number Calc」· 代码 · 共 128 行

NAME
    #

SYNOPSIS
    #!/usr/local/src/cmd/calc/calc -q -f
    # x
    x # y
    ## comment

TYPES
    x, y		integer or real

    return		integer (uniary operator case)
			integer or real (binary operator case)

DESCRIPTION
    The pound sign or sharp sign "#" has special meaning in calc.

    As a uniary operator:

    	# value

    returns the number of 1 bits, or pop-count of the absolute value of
    the numerator (abs(num(value))).  Therefore when x is a non-negative
    integer , # x is the pop-count of x.  And thus when x is a negative
    integer, # x returns the pop-count of abs(x).  And in the general
    case when x is a real, # x returns the pop-count of abs(num(x)).

    As a binary operator:

	x # y

    returns abs(x-y), the absolute value of the difference.

    When two or more pound signs in a row start a comment:

	## this is a comment
	### this is also a comment
	print "this will print";  ## but this will not because it is a comment

    A pound sign followed by a bang also starts a comment:

	#! strictly speaking, this is a comment
	print "this is correct but not recommended" #! acts like ##

    On POSIX / Un*X / Linux / BSD conforming systems, when an executable
    starts with the two bytes # and !, the remainder of the 1st line
    (up to an operating system imposed limit) is taken to be the path
    to the shell (plus shell arguments) that is to be executed.  The
    kernel appends the filename of the executable as a final argument
    to the shell.

    For example, of an executable file contains:

    	#!/usr/local/src/cmd/calc/calc -q -f
	/* NOTE: The #! above must start in column 1 of the 1st line */
	/* 	 The 1st line must end with -f */
	## Single # shell comments don't work, use two or more
	print "2+2 =", 2+2;

    When the above file it is executed by the kernel, it will print:

	2+2 = 4

    Such files are known to calc as cscripts.  See "help cscript"
    for examples.

    It is suggested that the -q be added to the first line to
    disable the reading of the startup scripts.  It is not mandatory.

    The last argument of the first line must be -f without the filename
    because the kernel will supply the cscript filename as a final
    argument.  The final -f also implies -s.  See "help usage" for
    more information.


EXAMPLE
    ; #3
	2
    ; #3.5
	3
    ; 4 # 5
	1
    ; 5 # 4
	1

    ; pi() # exp(1)
	0.4233108251307480031
    ; exp(1) # pi()
	0.4233108251307480031

    ; ## this is a comment

LIMITS
    none

LINK LIBRARY
    none

SEE ALSO
    cscript, unexpected, usage

## Copyright (C) 2007  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
##
## @(#) $Revision: 29.1 $
## @(#) $Id: pound,v 29.1 2007/02/06 23:48:15 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/pound,v $
##
## Under source code control:	2007/02/06 14:09
## File existed as early as:	2007
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/