Table of Contents
dc - an arbitrary precision calculator
dc
is a reverse-polish desk calculator which supports unlimited
precision arithmetic. It also allows you to define and call macros. Normally
reads from the standard input; if any command arguments are given to it,
they are filenames, and reads and executes the contents of the files before
reading from standard input. All normal output is to standard output; all
error output is to standard error.
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 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 meaning 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.
- n
- Prints the value on the top of the stack, popping it
off, and does not print a newline after.
- P
- Pops off the value on top of
the stack. If it it a string, it is simply printed without a trailing newline.
Otherwise it is a number, and the integer portion of its absolute value
is printed out as a "base (UCHAR_MAX+1)" byte stream. Assuming that (UCHAR_MAX+1)
is 256 (as it is on most machines with 8-bit bytes), the sequence KSK 0k1/
[_1*]sx d0>x [256~aPd0<x]dsxx sxLKk could also accomplish this function,
except for the side-effect of clobbering the x register.
- f
- Prints the entire
contents of the stack 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.
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 arguments, 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 depends on the current precision value and
the number of fraction digits in the two arguments.
- /
- 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.
- %
- Pops
two values, computes the remainder of the division that the / command would
do, and pushes that. The value computed is the same as that computed by
the sequence Sd dld/ Ld*- .
- ~
- Pops two values, divides the second one popped
from the first one popped. The quotient is pushed first, and the remainder
is pushed next. The number of fraction digits used in the division is specified
by the precision value. (The sequence SdSn lnld/ LnLd% could also accomplish
this function, with slightly different error checking.)
- ^
- 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.
- |
- Pops three values and computes a modular exponentiation. The first value
popped is used as the reduction modulus; this value must be a non-zero number,
and should be an integer. The second popped is used as the exponent; this
value must be a non-negative number, and any fractional part of this exponent
will be ignored. The third value popped is the base which gets exponentiated,
which should be an integer. For small integers this is like the sequence
Sm^Lm%, but, unlike ^, this command will work with arbritrarily large exponents.
- v
- Pops one value, computes its square root, and pushes that. The precision
value specifies the number of fraction digits in the result.
Most arithmetic
operations are affected by the ``precision value'', 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.
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.
- r
- Reverses the order of (swaps) the top two values
on the stack.
Registers
provides at least 256 memory registers, each named
by a single character. You can store a number or a string 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 inaccessible.
- 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 lr command.
Parameters
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. The input radix must be
between 2 and 16 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.
- i
- Pops the value off the
top of the stack and uses it to set the input radix.
- o
- Pops the value off
the top of the stack and uses it to set the output radix.
- k
- Pops the value
off the top of the stack and uses it to set the precision.
- I
- Pushes the
current input radix on the stack.
- O
- Pushes the current output radix on the
stack.
- K
- Pushes the current precision on the stack.
Strings
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 commands). All registers and the stack can
hold strings, and 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 (contained between balanced [ and ] characters), and pushes
it on the stack. For example, [foo]P prints the characters foo (with no
newline).
- a
- The top-of-stack is popped. If it was a number, then the low-order
byte of this number is converted into a string and pushed onto the stack.
Otherwise the top-of-stack was a string, and the first character of that
string is pushed back.
- 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 this 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
original top-of-stack is greater. Thus, 1 2>a will invoke register a's contents
and 2 1>a will not.
- !>r
- Similar but invokes the macro if the original top-of-stack
is not greater than (less than or equal to) what was the second-to-top.
- <r
- Similar but invokes the macro if the original top-of-stack is less.
- !<r
- Similar
but invokes the macro if the original top-of-stack is not less than (greater
than or equal to) what was the second-to-top.
- =r
- Similar but invokes the macro
if the two numbers popped are equal.
- !=r
- Similar but invokes the macro if
the two numbers popped are not equal.
- ?
- Reads a line from the terminal and
executes it. This command allows a macro to request input from the user.
- q
- exits from a 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 q command will cause to exit.
- 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. The Q command will never cause to exit.
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 0.
- z
- Pushes the
current stack depth: the number of objects on the stack before the execution
of the z command.
Miscellaneous
- !
- Will run the rest of the line as a system
command. Note that parsing of the !<, !=, and !> commands take precidence,
so if you want to run a command starting with <, =, or > you will need to
add a space after the !.
- #
- Will interpret the rest of the line as a comment.
- :r
- Will pop the top two values off of the stack. The old second-to-top value
will be stored in the array r, indexed by the old top-of-stack value.
- ;r
- Pops
the top-of-stack and uses it as an index into the array r. The selected value
is then pushed onto the stack.
Note that each stacked instance of a register
has its own array associated with it. Thus 1 0:a 0Sa 2 0:a La 0;ap will
print 1, because the 2 was stored in an instance of 0:a that was later
popped. BUGS
Email bug reports to bug-gnu-utils@prep.ai.mit.edu. Be sure to include
the word ``dc'' somewhere in the ``Subject:'' field.
Table of Contents