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Manual Pages for UNIX Darwin command on man integer

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

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 hard-

ware, it can make a big difference in performance. Note that this only affects how most of the arithmetic and relational ooppeerraattoorrss handle their operands and results, and nnoott 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 nnoott 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 uunnssiiggnneedd

integers, but with "use integer;" the operands and results are ssiiggnneedd.

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 opera-

tions may not be preserved. One common source of trouble is the modu-

lus 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 v5.8.8 2001-09-21 integer(3pm)




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