Index for Section 3

Alphabetical listing for I

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integer(3)
NAME
  integer - Perl pragma to use integer arithmetic instead of floating point

SYNOPSIS
      use integer;
      $x = 10/3;
      # $x is now 3, not 3.33333333333333333

DESCRIPTION
  This tells the compiler to use integer operations from here to the end of
  the enclosing BLOCK.	On many machines, this doesn't matter a great deal
  for most computations, but on those without floating point hardware, it can
  make a big difference in performance.

  Note that this only affects how most of the arithmetic and relational
  operators handle their operands and results, and not how all numbers
  everywhere are treated.  Specifically, "use integer;" has the effect that
  before computing the results of the arithmetic operators (+, -, *, /, %,
  +=, -=, *=, /=, %=, and unary minus), the comparison operators (<, <=, >,
  >=, ==, !=, <=>), and the bitwise operators (|, &, ^, <<, >>, |=, &=, ^=,
  <<=, >>=), the operands have their fractional portions truncated (or
  floored), and the result will have its fractional portion truncated as
  well.	 In addition, the range of operands and results is restricted to that
  of familiar two's complement integers, i.e., -(2**31) .. (2**31-1) on
  32-bit architectures, and -(2**63) .. (2**63-1) on 64-bit architectures.
  For example, this code

      use integer;
      $x = 5.8;
      $y = 2.5;
      $z = 2.7;
      $a = 2**31 - 1;  # Largest positive integer on 32-bit machines
      $, = ", ";
      print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;

  will print:  5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648

  Note that $x is still printed as having its true non-integer value of 5.8
  since it wasn't operated on.	And note too the wrap-around from the largest
  positive integer to the largest negative one.	  Also, arguments passed to
  functions and the values returned by them are not affected by "use
  integer;".  E.g.,

      srand(1.5);
      $, = ", ";
      print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);

  will give the same result with or without "use integer;"  The power
  operator "**" is also not affected, so that 2 ** .5 is always the square
  root of 2.  Now, it so happens that the pre- and post- increment and
  decrement operators, ++ and --, are not affected by "use integer;" either.
  Some may rightly consider this to be a bug -- but at least it's a long-
  standing one.

  Finally, "use integer;" also has an additional affect on the bitwise
  operators.  Normally, the operands and results are treated as unsigned
  integers, but with "use integer;" the operands and results are signed.
  This means, among other things, that ~0 is -1, and -2 & -5 is -6.

  Internally, native integer arithmetic (as provided by your C compiler) is
  used.	 This means that Perl's own semantics for arithmetic operations may
  not be preserved.  One common source of trouble is the modulus of negative
  numbers, which Perl does one way, but your hardware may do another.

      % perl -le 'print (4 % -3)'
      -2
      % perl -Minteger -le 'print (4 % -3)'
      1

  See the Pragmatic Modules entry in the perlmodlib manpage, the Integer
  Arithmetic entry in the perlop manpage

Index for Section 3

Alphabetical listing for I

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