


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


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.  Specifi-
       cally, "use integer;" has the effect that before computing
       the results of the arithmetic operators (+, -, *, /, %,
       +=, -=, *=, /=, %=, and unary minus), the comparison oper-
       ators (<, <=, >, >=, ==, !=, <=>), and the bitwise opera-
       tors (|, &, ^, <<, >>, |=, &=, ^=, <<=, >>=), 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 exam-
       ple, 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-inte-
       ger 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);



2001-05-24                 perl v5.6.1                          1





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


       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 com-
       mon 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






























2001-05-24                 perl v5.6.1                          2


