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@setfilename dc.info
@settitle dc, an arbitrary precision calculator
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@ifinfo
This file documents @sc{dc}, an arbitrary precision calculator.

Published by the Free Software Foundation,
675 Massachusetts Avenue,
Cambridge, MA 02139 USA

Copyright (C) 1984 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo

@setchapternewpage off

@titlepage
@title dc, an arbitrary precision calculator

@author by Ken Pizzini
@author manual by Richard Stallman
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1994 Free Software Foundation, Inc.

@sp 2
Published by the Free Software Foundation, @*
675 Massachusetts Avenue, @*
Cambridge, MA 02139 USA

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.

@end titlepage
@page

@node Top, Introduction, (dir), (dir)

@menu
* Introduction::                Introduction
* Printing Commands::           Printing Commands
* Arithmetic::                  Arithmetic
* Stack Control::               Stack Control
* Registers::                   Registers
* Parameters::                  Parameters
* Strings::                     Strings
* Status Inquiry::              Status Inquiry
* Miscellaneous::               Other commands
* Notes::                       Notes
@end menu

@node Introduction, Printing Commands, Top, Top
@comment  node-name,  next,  previous,  up
@chapter Introduction

@sc{dc} is a reverse-polish desk calculator
which supports unlimited precision arithmetic.
It also allows you to define and call macros.
Normally @sc{dc} reads from the standard input;
if any command arguments are given to it, they are filenames,
and @sc{dc} reads and executes the contents of the files
before reading from standard input.
All normal output is to standard output;
all error messages are written to standard error.

To exit, use @samp{q}.
@kbd{C-c} does not exit;
it is used to abort macros that are looping, etc.
(Currently this is not true; @kbd{C-c} does exit.)

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

To enter a number in @sc{dc}, type the digits,
with an optional decimal point.
Exponential notation is not supported.
To enter a negative number, begin the number with @samp{_}.
@samp{-} 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 meaning as commands.

@node Printing Commands, Arithmetic, Introduction, Top
@chapter Printing Commands

@table @samp
@item p
Prints the value on the top of the stack,
without altering the stack.
A newline is printed after the value.

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

@item f
Prints the entire contents of the stack
@c 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 command has been.
@end table

@node Arithmetic, Stack Control, Printing Commands, Top
@chapter Arithmetic

@table @samp
@item +
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 arguments, and is enough to be exact.

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

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

@item /
Pops two values, divides the second one popped
from the first one popped, and pushes the result.
The number of fraction digits is specified by the precision value.

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

@item ^
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 value specifies the number of fraction
digits in the result.

@item v
Pops one value, computes its square root, and pushes that.
The precision value specifies the number of fraction digits
in the result.
@end table

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

The remainder operation (@samp{%}) requires some explanation:
applied to arguments @samp{a} and @samp{b}
it produces @samp{a - (b * (a / b))},
where @samp{a / b} is computed in the current precision.

@node Stack Control, Registers, Arithmetic, Top
@chapter Stack Control

@table @samp
@item c
Clears the stack, rendering it empty.

@item d
Duplicates the value on the top of the stack,
pushing another copy of it.
Thus, @samp{4d*p} computes 4 squared and prints it.
@end table

@node Registers, Parameters, Stack Control, Top
@chapter Registers

@sc{dc} provides 256 memory registers, each named by a single character.
You can store a number in a register and retrieve it later.

@table @samp
@item s@var{r}
Pop the value off the top of the stack and
store it into register @var{r}.

@item l@var{r}
Copy the value in register @var{r},
and push it onto the stack.
This does not alter the contents of @var{r}.

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

@item S@var{r}
Pop the value off the top of the (main) stack and
push it onto the stack of register @var{r}.
The previous value of the register becomes inaccessible.

@item L@var{r}
Pop the value off the top of register @var{r}'s stack
and push it onto the main stack.
The previous value in register @var{r}'s stack, if any,
is now accessible via the @samp{l@var{r}} command.
@end table
@c 
@c The @samp{f} command prints a list of all registers that have contents
@c stored in them, together with their contents.
@c Only the current contents of each register (the top of its stack)
@c is printed.

@node Parameters, Strings, Registers, Top
@chapter Parameters

@sc{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;
@emph{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.
The input radix must be between 2 and 36 inclusive.
The output radix must be at least 2.
The precision must be zero or greater.
The precision is always measured in decimal digits,
regardless of the current input or output radix.

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

@item o
Pops the value off the top of the stack
and uses it to set the output radix.

@item k
Pops the value off the top of the stack
and uses it to set the precision.

@item I
Pushes the current input radix on the stack.

@item O
Pushes the current output radix on the stack.

@item K
Pushes the current precision on the stack.

@end table

@node Strings, Status Inquiry, Parameters, Top
@chapter Strings

@sc{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 @sc{dc} commands).
Both registers and the stack can hold strings,
and @sc{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 @samp{p} command can accept either and prints the object
according to its type.

@table @samp
@item [@var{characters}]
Makes a string containing @var{characters} and pushes it on the stack.
For example, @samp{[foo]P} prints the characters @samp{foo}
(with no newline).

@item 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, @samp{[1p]x} executes the macro @samp{1p},
which pushes 1 on the stack and prints @samp{1} on a separate line.

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

@item >@var{r}
Pops two values off the stack and compares them
assuming they are numbers,
executing the contents of register @var{r} as a macro
if the original top-of-stack is greater.
Thus, @samp{1 2>a} will invoke register @samp{a}'s contents
and @samp{2 1>a} will not.

@item <@var{r}
Similar but invokes the macro if the original top-of-stack is less.

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

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

@item q
During the execution of a macro,
this command exits from the macro and also from the macro which invoked it.
If called from the top level,
or from a macro which was called directly from the top level,
the @samp{q} command will cause @sc{dc} to exit.

@item Q
Pops a value off the stack and uses it as a count
of levels of macro execution to be exited.
Thus, @samp{3Q} exits three levels.
@end table

@node Status Inquiry, Miscellaneous, Strings, Top
@chapter Status Inquiry

@table @samp
@item 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.

@item 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
@c -1.
0.

@item z
Pushes the current stack depth;
the number of objects on the stack
before the execution of the @samp{z} command.
@end table

@node Miscellaneous, Notes, Status Inquiry, Top
@chapter Miscellaneous

@table @samp
@item !
Will run the rest of the line as a system command.

@item #
Will interpret the rest of the line as a comment.

@item :@var{r}
Will pop the top two values off of the stack.
The old second-to-top value will be stored in the array @var{r},
indexed by the old top-of-stack value.

@item ;@var{r}
Pops the top-of-stack and uses it as an index into
the array @var{r}.
The selected value is then pushed onto the stack.
@end table

@node Notes,  , Miscellaneous, Top
@chapter Notes

The array operations @samp{:} and @samp{;} are usually
only used by traditional implementations of BC.
(The GNU BC is self contained and does not need @sc{dc} to run.)
The comment operator @samp{#} is a new command
not found in traditional implementations of @sc{dc}.

@contents
@bye
