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**311) on 32bit architectures, and
(2**63) .. (2**631) on 64bit 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 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 noninte
ger 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);
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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 longstanding 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 "Pragmatic Modules" in perlmodlib, "Integer Arith
metic" in perlop
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