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DC(1)									 DC(1)

NAME
       dc, An Arbitrary	Precision Calculator

SYNOPSIS
       dc

DESCRIPTION
       DC  is a	reverse-polish desk calculator which supports unlimited	preci-
       sion arithmetic.	 It also allows	you to define and call	macros.	  Nor-
       mally  DC  reads	 from the standard input; if any command arguments are
       given to	it, they are filenames,	and DC reads and executes the contents
       of  the	files  before  reading	from standard input.  All output is to
       standard	output.

       A reverse-polish	calculator stores numbers on a stack.  Entering	a num-
       ber  pushes  it	on the stack.  Arithmetic operations pop arguments off
       the stack and push the results.

       To enter	a number in DC,	type the  digits,  with	 an  optional  decimal
       point.	Exponential  notation  is  not supported.  To enter a negative
       number, begin the number	with `_'.  `-' cannot be used for this,	as  it
       is  a binary operator for subtraction instead.  To enter	two numbers in
       succession, separate them with spaces or	newlines.  These have no mean-
       ing as commands.

Printing Commands
       p Prints	the value on the top of	the stack, without altering the	stack.
       A newline is printed after the value.

       P Prints	the value on the top of	the stack, popping it  off,  and  does
       not print a newline after.

       f  Prints  the  entire contents of the stack and	the contents of	all of
       the registers, without altering anything.  This is a  good  command  to
       use  if you are lost or want to figure out what the effect of some com-
       mand has	been.

Arithmetic
       + Pops two values off the stack,	adds them, and pushes the result.  The
       precision  of  the result is determined only by the values of the argu-
       ments, and is enough to be exact.

       - Pops two values, subtracts the	first one popped from the  second  one
       popped, and pushes the result.

       *  Pops two values, multiplies them, and	pushes the result.  The	number
       of fraction digits in the result	is controlled by the current precision
       flag (see below)	and does not depend on the values being	multiplied.

       /  Pops	two  values,  divides the second one popped from the first one
       popped, and pushes the result.  The number of fraction digits is	speci-
       fied by the precision flag.

       %  Pops	two  values, computes the remainder of the division that the /
       command would do, and pushes that.  The division	is done	with  as  many
       fraction	 digits	 as the	precision flag specifies, and the remainder is
       also computed with that many fraction digits.

       ^ Pops two values and exponentiates, using the first  value  popped  as
       the  exponent  and the second popped as the base.  The fraction part of
       the exponent is ignored.	 The precision flag specifies  the  number  of
       fraction	digits in the result.

       v  Pops one value, computes its square root, and	pushes that.  The pre-
       cision flag specifies the number	of fraction digits in the result.

       Most arithmetic operations are affected by the "precision flag",	 which
       you  can	 set with the k	command.  The default precision	value is zero,
       which means that	all arithmetic except  for  addition  and  subtraction
       produces	integer	results.

       The  remainder  operation % requires some explanation: applied to argu-
       ments `a' and `b' it produces `a	- (b * (a / b))', where	 `a  /	b'  is
       computed	in the current precision.

Stack Control
       c Clears	the stack, rendering it	empty.

       d Duplicates the	value on the top of the	stack, pushing another copy of
       it.  Thus, `4d*p' computes 4 squared and	prints it.

Registers
       DC provides 128 memory registers, each named by a single	ASCII  charac-
       ter.  You can store a number in a register and retrieve it later.

       sr Pop the value	off the	top of the stack and store it into register r.

       lr Copy the value in register r and push	it onto	the stack.  This  does
       not alter the contents of r.

       Each  register also contains its	own stack.  The	current	register value
       is the top of the register's stack.

       Sr Pop the value	off the	top of the (main) stack	and push it  onto  the
       stack  of register r.  The previous value of the	register becomes inac-
       cessible.

       Lr Pop the value	off the	top of register	r's stack and push it onto the
       main  stack.   The previous value in register r's stack,	if any,	is now
       accessible via the Ir command.

       The f command prints a list of all registers that have contents	stored
       in  them,  together  with their contents.  Only the current contents of
       each register (the top of its stack) is printed.

Parameters
       DC has three parameters that control its	operation: the precision,  the
       input  radix, and the output radix.  The	precision specifies the	number
       of fraction digits to keep in the result	of most	arithmetic operations.
       The  input  radix controls the interpretation of	numbers	typed in; all-
       numbers typed in	use this radix.	 The output radix is used for printing
       numbers.

       The input and output radices are	separate parameters; you can make them
       unequal,	which can be useful or confusing.  Each	radix must be  between
       2 and 36	inclusive.  The	precision must be zero or greater.  The	preci-
       sion is always measured in decimal digits, regardless  of  the  current
       input or	output radix.

       i  Pops the value off the top of	the stack and uses it to set the input
       radix.

       o

       k Similarly set the output radix	and the	precision.

       I Pushes	the current input radix	on the stack.

       O

       K Similarly push	the current output radix and the current precision.

Strings
       DC can operate on strings as well as on numbers.	 The only  things  you
       can  do	with  strings are print	them and execute them as macros	(which
       means that the contents of the string are processed  as	DC  commands).
       Both  registers	and  the  stack	 can hold strings, and DC always knows
       whether any given object	is a string or a number.  Some	commands  such
       as  arithmetic  operations demand numbers as arguments and print	errors
       if given	strings.  Other	commands can  accept  either  a	 number	 or  a
       string;	for  example,  the  p command can accept either	and prints the
       object according	to its type.

       [characters] Makes a string containing characters and pushes it on  the
       stack.	For  example,  [foo]p  prints the characters foo (with no new-
       line).

       x Pops a	value off the stack and	executes it as a macro.	  Normally  it
       should  be  a  string; if it is a number, it is simply pushed back onto
       the stack.  For example,	[1p]x executes the macro 1p which pushes 1  on
       the stack and prints 1 on a separate line.

       Macros  are  most  often	 stored	in registers; [1p]sa stores a macro to
       print 1 into register a,	and lax	invokes	the macro.

       >r Pops two values off the stack	and compares them  assuming  they  are
       numbers,	 executing the contents	of register r as a macro if the	origi-
       nal top-of-stack	is greater.  Thus, 1 2>a will invoke register a's con-
       tents and 2 1>a will not.

       <r  Similar but invokes the macro if the	original top-of-stack is less.

       =r Similar but invokes the macro	if the two numbers popped  are	equal.
       This can	also be	validly	used to	compare	two strings for	equality.

       ?  Reads	a line from the	terminal and executes it.  This	command	allows
       a macro to request input	from the user.

       q During	the execution of a  macro,  this  comand  does	not  exit  DC.
       Instead,	it exits from that macro and also from the macro which invoked
       it (if any).

       Q Pops a	value off the stack and	uses it	as a count of levels of	 macro
       execution to be exited.	Thus, 3Q exits three levels.

Status Inquiry
       Z  Pops	a  value off the stack,	calculates the number of digits	it has
       (or number of characters, if it is a string) and	pushes that number.

       X Pops a	value off the stack, calculates	the number of fraction	digits
       it  has,	and pushes that	number.	 For a string, the value pushed	is -1.

       z Pushes	the current stack depth; the number of objects	on  the	 stack
       before the execution of the z command.

       I Pushes	the current value of the input radix.

       O Pushes	the current value of the output	radix.

       K Pushes	the current value of the precision.

Notes
       The  :  and ; commands of the Unix DC program are not supported,	as the
       documentation does not say what they do.	 The !	command	 is  not  sup-
       ported, but will	be supported as	soon as	a library for executing	a line
       as a command exists.

BUGS
       Email bug reports to bug-gnu-utils@prep.ai.mit.edu.  Be sure to include
       the word	``dc'' somewhere in the	``Subject:'' field.

GNU Project			  03 Aug 1993				 DC(1)

NAME | SYNOPSIS | DESCRIPTION | Printing Commands | Arithmetic | Stack Control | Registers | Parameters | Strings | Status Inquiry | Notes | BUGS

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