396 lines
9.1 KiB
Groff
396 lines
9.1 KiB
Groff
.TH DC 1 "07 Apr 1994" "GNU Project"
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.ds dc \fIdc\fP
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.ds Dc \fIDc\fP
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.SH
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NAME
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dc \- an arbitrary precision calculator
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.SH
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SYNOPSIS
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dc
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.SH
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DESCRIPTION
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.PP
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\*(Dc is a reverse-polish desk calculator which supports
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unlimited precision arithmetic.
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It also allows you to define and call macros.
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Normally \*(dc reads from the standard input;
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if any command arguments are given to it, they are filenames,
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and \*(dc reads and executes the contents of the files before reading
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from standard input.
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All normal output is to standard output;
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all error output is to standard error.
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.PP
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A reverse-polish calculator stores numbers on a stack.
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Entering a number pushes it on the stack.
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Arithmetic operations pop arguments off the stack and push the results.
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.PP
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To enter a number in
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.IR dc ,
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type the digits with an optional decimal point.
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Exponential notation is not supported.
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To enter a negative number,
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begin the number with ``_''.
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``-'' cannot be used for this,
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as it is a binary operator for subtraction instead.
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To enter two numbers in succession,
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separate them with spaces or newlines.
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These have no meaning as commands.
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.PD
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.SH
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Printing Commands
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.TP
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.B p
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Prints the value on the top of the stack,
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without altering the stack.
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A newline is printed after the value.
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.TP
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.B P
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Prints the value on the top of the stack, popping it off,
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and does not print a newline after.
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.TP
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.B f
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Prints the entire contents of the stack
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.ig
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and the contents of all of the registers,
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..
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without altering anything.
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This is a good command to use if you are lost or want
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to figure out what the effect of some command has been.
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.PD
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.SH
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Arithmetic
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.TP
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.B +
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Pops two values off the stack, adds them,
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and pushes the result.
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The precision of the result is determined only
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by the values of the arguments,
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and is enough to be exact.
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.TP
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.B -
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Pops two values,
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subtracts the first one popped from the second one popped,
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and pushes the result.
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.TP
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.B *
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Pops two values, multiplies them, and pushes the result.
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The number of fraction digits in the result is controlled
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by the current precision value (see below) and does not
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depend on the values being multiplied.
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.TP
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.B /
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Pops two values,
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divides the second one popped from the first one popped,
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and pushes the result.
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The number of fraction digits is specified by the precision value.
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.TP
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.B %
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Pops two values,
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computes the remainder of the division that the
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.B /
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command would do,
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and pushes that.
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The division is done with as many fraction digits
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as the precision value specifies,
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and the remainder is also computed with that many fraction digits.
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.TP
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.B ^
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Pops two values and exponentiates,
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using the first value popped as the exponent
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and the second popped as the base.
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The fraction part of the exponent is ignored.
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The precision value specifies the number of fraction
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digits in the result.
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.TP
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.B v
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Pops one value,
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computes its square root,
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and pushes that.
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The precision value specifies the number of fraction digits in the result.
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.PP
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Most arithmetic operations are affected by the ``precision value'',
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which you can set with the
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.B k
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command.
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The default precision value is zero,
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which means that all arithmetic except for
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addition and subtraction produces integer results.
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.PP
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The remainder operation
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.B %
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requires some explanation:
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applied to arguments ``a'' and ``b'' it produces ``a - (b * (a / b))'',
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where ``a / b'' is computed in the current precision.
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.SH
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Stack Control
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.TP
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.B c
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Clears the stack, rendering it empty.
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.TP
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.B d
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Duplicates the value on the top of the stack,
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pushing another copy of it.
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Thus, ``4d*p'' computes 4 squared and prints it.
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.SH
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Registers
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.PP
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\*(Dc provides 256 memory registers,
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each named by a single character.
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You can store a number or a string in a register and retrieve it later.
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.TP
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.BI s r
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Pop the value off the top of the stack and store
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it into register
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.IR r .
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.TP
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.BI l r
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Copy the value in register
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.I r
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and push it onto the stack.
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This does not alter the contents of
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.IR r .
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.PP
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Each register also contains its own stack.
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The current register value is the top of the register's stack.
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.TP
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.BI S r
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Pop the value off the top of the (main) stack and
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push it onto the stack of register
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.IR r .
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The previous value of the register becomes inaccessible.
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.TP
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.BI L r
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Pop the value off the top of register
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.IR r 's
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stack and push it onto the main stack.
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The previous value
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in register
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.IR r 's
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stack, if any,
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is now accessible via the
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.BI l r
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command.
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.ig
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.PP
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The
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.B f
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command prints a list of all registers that have contents stored in them,
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together with their contents.
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Only the current contents of each register
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(the top of its stack)
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is printed.
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..
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.SH
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Parameters
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.PP
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\*(Dc has three parameters that control its operation:
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the precision, the input radix, and the output radix.
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The precision specifies the number
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of fraction digits to keep in the result of most arithmetic operations.
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The input radix controls the interpretation of numbers typed in;
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all numbers typed in use this radix.
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The output radix is used for printing numbers.
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.PP
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The input and output radices are separate parameters;
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you can make them unequal,
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which can be useful or confusing.
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The input radix must be between 2 and 36 inclusive.
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The output radix must be at least 2.
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The precision must be zero or greater.
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The precision is always measured in decimal digits,
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regardless of the current input or output radix.
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.TP
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.B i
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Pops the value off the top of the stack
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and uses it to set the input radix.
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.TP
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.B o
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Pops the value off the top of the stack
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and uses it to set the output radix.
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.TP
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.B k
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Pops the value off the top of the stack
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and uses it to set the precision.
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.TP
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.B I
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Pushes the current input radix on the stack.
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.TP
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.B O
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Pushes the current output radix on the stack.
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.TP
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.B K
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Pushes the current precision on the stack.
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.SH
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Strings
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.PP
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\*(Dc can operate on strings as well as on numbers.
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The only things you can do with strings are
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print them and execute them as macros
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(which means that the contents of the string are processed as
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\*(dc commands).
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All registers and the stack can hold strings,
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and \*(dc always knows whether any given object is a string or a number.
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Some commands such as arithmetic operations demand numbers
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as arguments and print errors if given strings.
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Other commands can accept either a number or a string;
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for example, the
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.B p
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command can accept either and prints the object
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according to its type.
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.TP
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.BI [ characters ]
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Makes a string containing
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.I characters
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(contained between balanced
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.B [
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and
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.B ]
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characters),
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and pushes it on the stack.
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For example,
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.B [foo]P
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prints the characters
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.B foo
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(with no newline).
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.TP
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.B x
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Pops a value off the stack and executes it as a macro.
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Normally it should be a string;
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if it is a number,
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it is simply pushed back onto the stack.
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For example,
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.B [1p]x
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executes the macro
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.B 1p
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which pushes
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.B 1
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on the stack and prints
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.B 1
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on a separate line.
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.PP
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Macros are most often stored in registers;
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.B [1p]sa
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stores a macro to print
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.B 1
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into register
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.BR a ,
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and
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.B lax
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invokes this macro.
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.TP
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.BI > r
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Pops two values off the stack and compares them
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assuming they are numbers,
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executing the contents of register
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.I r
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as a macro if the original top-of-stack
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is greater.
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Thus,
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.B 1 2>a
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will invoke register
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.BR a 's
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contents and
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.B 2 1>a
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will not.
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.TP
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.BI < r
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Similar but invokes the macro if the original top-of-stack is less.
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.TP
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.BI = r
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Similar but invokes the macro if the two numbers popped are equal.
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.ig
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This can also be validly used to compare two strings for equality.
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..
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.TP
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.B ?
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Reads a line from the terminal and executes it.
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This command allows a macro to request input from the user.
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.TP
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.B q
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exits from a macro and also from the macro which invoked it.
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If called from the top level,
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or from a macro which was called directly from the top level,
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the
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.B q
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command will cause \*(dc to exit.
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.TP
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.B Q
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Pops a value off the stack and uses it as a count
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of levels of macro execution to be exited.
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Thus,
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.B 3Q
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exits three levels.
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The
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.B Q
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command will never cause \*(dc to exit.
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.SH
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Status Inquiry
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.TP
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.B Z
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Pops a value off the stack,
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calculates the number of digits it has
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(or number of characters, if it is a string)
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and pushes that number.
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.TP
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.B X
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Pops a value off the stack,
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calculates the number of fraction digits it has,
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and pushes that number.
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For a string,
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the value pushed is
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.\" -1.
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0.
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.TP
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.B z
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Pushes the current stack depth;
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the number of objects on the stack before the execution of the
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.B z
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command.
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.SH
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Miscellaneous
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.TP
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.B !
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Will run the rest of the line as a system command.
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.TP
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.B #
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Will interpret the rest of the line as a comment.
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.TP
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.BI : r
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Will pop the top two values off of the stack.
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The old second-to-top value will be stored in the array
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.IR r ,
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indexed by the old top-of-stack value.
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.TP
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.BI ; r
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Pops the top-of-stack and uses it as an index into
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the array
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.IR r .
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The selected value is then pushed onto the stack.
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.SH
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NOTES
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.PP
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The array operations
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.B :
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and
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.B ;
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are usually only used by traditional implementations of
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.IR bc .
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(The GNU
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.I bc
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is self contained and does not need \*(dc to run.)
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The comment operator
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.B #
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is a new command not found in traditional implementations of
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.IR dc .
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.SH
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BUGS
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.PP
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Email bug reports to
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.BR bug-gnu-utils@prep.ai.mit.edu .
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Be sure to include the word ``dc'' somewhere in the ``Subject:'' field.
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.SH HISTORY
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A
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.I dc
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command appeared in
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Version 1 AT&T UNIX.
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