integer(3perl)                   Perl Programmers Reference Guide                  integer(3perl)



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 "Pragmatic Modules" in perlmodlib, "Integer Arithmetic" in perlop



perl v5.20.2                                2014-12-27                             integer(3perl)