Table of Contents
dc - an arbitrary precision calculator
dc
[-V] [--version] [-h] [--help] [-e scriptexpression] [--expression=scriptexpression]
[-f scriptfile] [--file=scriptfile]
[file ...]
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 (using upper case letters A through F as "digits" when
working with input bases greater than ten), 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.
may be
invoked with the following command-line options:
- -V
- --version
- Print out the
version of that is being run and a copyright notice, then exit.
- -h
- --help
- Print a usage message briefly summarizing these command-line options and
the bug-reporting address, then exit.
- -e script
- --expression=script
- Add the
commands in script to the set of commands to be run while processing the
input.
- -f script-file
- --file=script-file
- Add the commands contained in the file
script-file to the set of commands to be run while processing the input.
If any command-line parameters remain after processing the above, these
parameters are interpreted as the names of input files to be processed.
A file name of - refers to the standard input stream. The standard input
will processed if no script files or expressions are specified. 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 KSK0k1/_1Ss [ls*]Sxd0>x [256~Ssd0<x]dsxxsx[q]Sq[Lsd0>qaPlxx]
dsxxsx0sqLqsxLxLK+k could also accomplish this function. (Much of the complexity
of the above native-dc code is due to the ~ computing the characters backwards,
and the desire to ensure that all registers wind up back in their original
states.)
- 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 arbitrarily 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. (This can also be
accomplished with the sequence SaSbLaLb.)
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
has a limited ability to 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. The digit count for a number
does not include any leading zeros, even if those appear to the right of
the radix point.
- 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 precedence, 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-dc@gnu.org.
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