1integer(3pm)           Perl Programmers Reference Guide           integer(3pm)
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NAME

6       integer - Perl pragma to use integer arithmetic instead of floating
7       point
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SYNOPSIS

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

15       This tells the compiler to use integer operations from here to the end
16       of the enclosing BLOCK.  On many machines, this doesn't matter a great
17       deal for most computations, but on those without floating point
18       hardware, it can make a big difference in performance.
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20       Note that this only affects how most of the arithmetic and relational
21       operators handle their operands and results, and not how all numbers
22       everywhere are treated.  Specifically, "use integer;" has the effect
23       that before computing the results of the arithmetic operators (+, -, *,
24       /, %, +=, -=, *=, /=, %=, and unary minus), the comparison operators
25       (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &, ^, <<,
26       >>, |=, &=, ^=, <<=, >>=), the operands have their fractional portions
27       truncated (or floored), and the result will have its fractional portion
28       truncated as well.  In addition, the range of operands and results is
29       restricted to that of familiar two's complement integers, i.e.,
30       -(2**31) .. (2**31-1) on 32-bit architectures, and -(2**63) ..
31       (2**63-1) on 64-bit architectures.  For example, this code
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33           use integer;
34           $x = 5.8;
35           $y = 2.5;
36           $z = 2.7;
37           $a = 2**31 - 1;  # Largest positive integer on 32-bit machines
38           $, = ", ";
39           print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;
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41       will print:  5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648
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43       Note that $x is still printed as having its true non-integer value of
44       5.8 since it wasn't operated on.  And note too the wrap-around from the
45       largest positive integer to the largest negative one.   Also, arguments
46       passed to functions and the values returned by them are not affected by
47       "use integer;".  E.g.,
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49           srand(1.5);
50           $, = ", ";
51           print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);
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53       will give the same result with or without "use integer;"  The power
54       operator "**" is also not affected, so that 2 ** .5 is always the
55       square root of 2.  Now, it so happens that the pre- and post- increment
56       and decrement operators, ++ and --, are not affected by "use integer;"
57       either.  Some may rightly consider this to be a bug -- but at least
58       it's a long-standing one.
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60       Finally, "use integer;" also has an additional affect on the bitwise
61       operators.  Normally, the operands and results are treated as unsigned
62       integers, but with "use integer;" the operands and results are signed.
63       This means, among other things, that ~0 is -1, and -2 & -5 is -6.
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65       Internally, native integer arithmetic (as provided by your C compiler)
66       is used.  This means that Perl's own semantics for arithmetic
67       operations may not be preserved.  One common source of trouble is the
68       modulus of negative numbers, which Perl does one way, but your hardware
69       may do another.
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71           % perl -le 'print (4 % -3)'
72           -2
73           % perl -Minteger -le 'print (4 % -3)'
74           1
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76       See "Pragmatic Modules" in perlmodlib, "Integer Arithmetic" in perlop
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80perl v5.12.4                      2011-06-01                      integer(3pm)
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