# 任意精度の計算機 dcを使いこなせるようになりたい

man dcで確認できるマニュアルを読破してdcコマンドを完全に使いこなせるようにしたいと思います。

```dc(1)                       General Commands Manual                      dc(1)

NAME
dc - an arbitrary precision calculator

SYNOPSIS
dc [-V] [--version] [-h] [--help]
[-e scriptexpression] [--expression=scriptexpression]
[-f scriptfile] [--file=scriptfile]
[file ...]

```

```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 normal output is
to standard output; all error output is to standard error.

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 (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 new‐
lines.  These have no meaning as commands.

```

ちょっと確認してみます。

```takk~\$ echo 10p | dc
10
takk~\$
```

スタックに10を積んで、スタックの一番を、pコマンドで表示してみました。
10が表示されましたね。

```takk~\$ echo 10 20 +p | dc
30
takk~\$
```

これは面白いですねえ。

では、man dcのマニュアルにしたがってオプションを確認していきます。

```OPTIONS
dc may be invoked with the following command-line options:

-V

--version
Print out the version of dc that is being run  and  a  copyright
notice, then exit.
```

バージョン表示ですね。ロングオプションの方も、ショートと同じなので省略しまｓ。

```takk~\$ dc -V
dc (GNU bc 1.07.1) 1.4.1

Copyright 1994, 1997, 1998, 2000, 2001, 2003-2006, 2008, 2010, 2012-2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE,
to the extent permitted by law.
```

```
-h

--help Print a usage message briefly summarizing these command-line op‐
tions and the bug-reporting address, then exit.

```

こちらもショートオプションだけ確認します。

```takk~\$ dc -h
Usage: dc [OPTION] [file ...]
-e, --expression=EXPR    evaluate expression
-f, --file=FILE          evaluate contents of file
-h, --help               display this help and exit
-V, --version            output version information and exit

Email bug reports to:  bug-dc@gnu.org .
takk~\$
```

ふむふむ。忘れなさそうなオプションだけが表示されるヘルプですねえ。

```       -e script

--expression=script
Add the commands in script to the set  of  commands  to  be  run
while processing the input.

```

スクリプトを直接指定できるんですね。

```takk~\$ dc -e '10 20 +p'
30
takk~\$
```

```takk~\$ dc <<< '10 20 +p'
30
takk~\$
```

ビミョーなところです。

```       -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.

```

スクリプトファイルが使えるとのこと。

```takk~\$ cat a.txt
10
20
+
p
takk~\$ dc -f a.txt
30
takk~\$
```

スクリプトファイルだと、後から計算式を見直すのに効率がよさそうです。

```       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 in‐
put will processed if no script files or expressions are specified.
```

すでに使い方が分かってたので先走りましたが、ここに使い方が書いてありますね。

では各オプションです。

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

```

```takk~\$ dc <<< '10 20 30 ppp'
30
30
30
takk~\$
```

pを3回実行しても、スタックを更新しないので、同じ値が3回表示されました。

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

```

```takk~\$ dc <<< '10 20 30 nnn'
302010takk~\$
```

スタックの一番上から順に取り出して表示されました。改行は表示されません。

```      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.)

```
```文字列は、文字列は[]で囲みます。Pで文字列を表示すると改行されません。
takk~\$ dc <<< '[HELLO] P'
HELLOtakk~\$
```
```      f      Prints  the  entire  contents of the stack without altering any‐
thing.  This is a good command to use if you are lost or want to
figure out what the effect of some command has been.
```

```takk~\$ dc <<< '10 20 30 f'
30
20
10
takk~\$
```
```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.

```

```takk~\$ dc <<< '10 20 30 +f'
50
10
takk~\$
```

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

```

5 – 3を計算してみます。

```takk~\$ dc <<< '5 3 -p'
2
takk~\$
```

```      *      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 ar‐
guments.

```

11 * 20です。

```takk~\$ dc <<< '11 20 *p'
220
takk~\$
```

```      /      Pops  two  values,  divides the second one popped from the first
one popped, and pushes the result.  The number of fraction  dig‐
its is specified by the precision value.

```

30 ÷ 2です。

```takk~\$ dc <<< '30 2 /p'
15
takk~\$
```

```      %      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*- .

```

5÷3の余りです。

```takk~\$ dc <<< '5 3 %p'
2
takk~\$
```

```      ~      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 differ‐
ent error checking.)
```

20 ÷ 3を実行してみます。

```takk~\$ dc <<< '20 3 ~f'
2
6
takk~\$
```

```      ^      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.

```

2の8乗を計算してみます。

```takk~\$ dc <<<'2 8 ^p'
256
takk~\$
```
```      |      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-nega‐
tive  number,  and  any fractional part of this exponent will be
ignored.  The third value popped is the base which gets exponen‐
tiated,  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.

```

13の2乗を5で割った余を求めてみます。

```takk~\$ dc <<<'13 2 5 |p'
4
takk~\$
```
```     v       Pops  one value, computes its square root, and pushes that.  The
maximum of the precision value and the precision of the argument
is  used  to  determine the number of fraction digits in the re‐
sult.

```

```takk~\$ dc <<<'9vp 25vp 36vp'
3
5
6
takk~\$
```

2の平方根を求めてみます。

```takk~\$ dc <<<'2vp'
1
takk~\$
```

1.4142…とはならずに、1が返りました。

```             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  subtrac‐
tion produces integer results.
```

kコマンドで精度を変えられるが、初期精度は整数になっているようです(k=0)。
さきほどの2の平方根の結果も、精度を変更すれば小数点以下が返ってくるということですね。

```takk~\$ dc <<<'5k 2vp'
1.41421
takk~\$
```

```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.)

R      Pops  the  top-of-stack as an integer n.  Cyclically rotates the
top n items on the updated stack.  If n is  positive,  then  the
rotation direction will make the topmost element the second-from
top; if n is negative, then the rotation will make  the  topmost
element  the  n-th  element from the top.  If the stack depth is
less than n, then the entire stack is rotated (in the  appropri‐
ate direction), without any error being reported.
```
```Registers
dc provides at least 256 memory registers, each named by a single char‐
acter.  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 regis‐
ter r.

lr     Copy the value in register r and push it onto  the  stack.   The
value  0  is  retrieved  if the register is uninitialized.  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 be‐
comes 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
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.  The input radix must be be‐
tween 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
dc  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
dc commands).  All registers and the stack can hold strings, and dc al‐
ways knows whether any given object is a string or a number.  Some com‐
mands such as arithmetic operations demand  numbers  as  arguments  and
print errors if given strings.  Other commands can accept either a num‐
ber 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  di‐
rectly from the top level, the q command will cause dc 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 dc to exit.
```
```Status Inquiry
Z      Pops  a  value  off  the stack, calculates the number of decimal
digits it has (or number of characters, if it is a  string)  and
pushes  that  number.  The digit count for a number does not in‐
clude 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 associ‐
ated 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.
```
```       FILES
~/.dcrc        The commands in this file will be executed  when  dc  is
first run.
```
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