MAN page from Fedora 24 perl-libs-5.22.2-359.fc24.x86_64.rpm


Section: Perl Programmers Reference Guide (3pm)
Updated: 2015-10-17


integer - Perl pragma to use integer arithmetic instead of floating point 


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


This tells the compiler to use integer operations from here to the endof the enclosing BLOCK. On many machines, this doesn't matter a greatdeal for most computations, but on those without floating pointhardware, it can make a big difference in performance.

Note that this only affects how most of the arithmetic and relationaloperators handle their operands and results, and not how allnumbers everywhere are treated. Specifically, "use integer;" has theeffect that before computing the results of the arithmetic operators(+, -, *, /, %, +=, -=, *=, /=, %=, and unary minus), the comparisonoperators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &,^, <<, >>, |=, &=, ^=, <<=, >>=), the operands have their fractionalportions truncated (or floored), and the result will have itsfractional portion truncated as well. In addition, the range ofoperands and results is restricted to that of familiar two's complementintegers, 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 of5.8 since it wasn't operated on. And note too the wrap-around from thelargest positive integer to the largest negative one. Also, argumentspassed to functions and the values returned by them are not affectedby "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 poweroperator "**" is also not affected, so that 2 ** .5 is always thesquare root of 2. Now, it so happens that the pre- and post- incrementand decrement operators, ++ and --, are not affected by "use integer;"either. Some may rightly consider this to be a bug --- but at least it'sa long-standing one.

Finally, "use integer;" also has an additional affect on the bitwiseoperators. Normally, the operands and results are treated asunsigned integers, but with "use integer;" the operands and resultsare 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 arithmeticoperations may not be preserved. One common source of trouble is themodulus of negative numbers, which Perl does one way, but your hardwaremay do another.

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

See ``Pragmatic Modules'' in perlmodlib, ``Integer Arithmetic'' in perlop




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