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(m4.info)Eval

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Evaluating integer expressions
==============================

   Integer expressions are evaluated with `eval':

     eval(EXPRESSION, opt RADIX, opt WIDTH)

which expands to the value of EXPRESSION.

   Expressions can contain the following operators, listed in order of
decreasing precedence.

`-'
     Unary minus

`**'
     Exponentiation

`*  /  %'
     Multiplication, division and modulo

`+  -'
     Addition and subtraction

`<<  >>'
     Shift left or right

`==  !=  >  >=  <  <='
     Relational operators

`!'
     Logical negation

`~'
     Bitwise negation

`&'
     Bitwise and

`^'
     Bitwise exclusive-or

`|'
     Bitwise or

`&&'
     Logical and

`||'
     Logical or

   All operators, except exponentiation, are left associative.

   Note that many `m4' implementations use `^' as an alternate operator
for the exponentiation, while many others use `^' for the bitwise
exclusive-or.  GNU `m4' changed its behavior: it used to exponentiate
for `^', it now computes the bitwise exclusive-or.

   Numbers without special prefix are given decimal.  A simple `0'
prefix introduces an octal number.  `0x' introduces an hexadecimal
number.  `0b' introduces a binary number.  `0r' introduces a number
expressed in any radix between 1 and 36: the prefix should be
immediately followed by the decimal expression of the radix, a colon,
then the digits making the number.  For any radix, the digits are `0',
`1', `2', ....  Beyond `9', the digits are `a', `b' ... up to `z'.
Lower and upper case letters can be used interchangeably in numbers
prefixes and as number digits.

   Parentheses may be used to group subexpressions whenever needed.
For the relational operators, a true relation returns `1', and a false
relation return `0'.

   Here are a few examples of use of `eval'.

     eval(-3 * 5)
     =>-15
     eval(index(`Hello world', `llo') >= 0)
     =>1
     define(`square', `eval(($1)**2)')
     =>
     square(9)
     =>81
     square(square(5)+1)
     =>676
     define(`foo', `666')
     =>
     eval(`foo'/6)
     error-->51.eval:14: m4: Bad expression in eval: foo/6
     =>
     eval(foo/6)
     =>111

   As the second to last example shows, `eval' does not handle macro
names, even if they expand to a valid expression (or part of a valid
expression).  Therefore all macros must be expanded before they are
passed to `eval'.

   If RADIX is specified, it specifies the radix to be used in the
expansion.  The default radix is 10.  The result of `eval' is always
taken to be signed.  The WIDTH argument specifies a minimum output
width.  The result is zero-padded to extend the expansion to the
requested width.

     eval(666, 10)
     =>666
     eval(666, 11)
     =>556
     eval(666, 6)
     =>3030
     eval(666, 6, 10)
     =>0000003030
     eval(-666, 6, 10)
     =>-000003030

   Take note that RADIX cannot be larger than 36.

   The builtin macro `eval' is recognized only when given arguments.