
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 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 opera
tors (+, , *, /, %, +=, =, *=, /=, %=, 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**311) on 32bit architectures, and (2**63) .. (2**631) on 64bit architectures. For
example, this code
use integer;
$x = 5.8;
$y = 2.5;
$z = 2.7;
$a = 2**31  1; # Largest positive integer on 32bit 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 noninteger value of 5.8 since it wasn't
operated on. And note too the wraparound 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 op
erands 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 "Pragmatic Modules" in perlmodlib, "Integer Arithmetic" in perlop
perl v5.8.0 20020601 integer(3pm) 
