1integer(3pm) Perl Programmers Reference Guide integer(3pm)
2
6 integer - Perl pragma to use integer arithmetic instead of floating
7 point
8
10 use integer;
11 $x = 10/3;
12 # $x is now 3, not 3.33333333333333333
13
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.
19 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
32 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;
40 will print: 5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648
42 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.,
48 srand(1.5);
50 $, = ", ";
51 print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);
52 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.
59 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.
64 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.
70 % perl -le 'print (4 % -3)'
72 -2
73 % perl -Minteger -le 'print (4 % -3)'
74 1
75 See "Pragmatic Modules" in perlmodlib, "Integer Arithmetic" in perlop
77perl v5.12.4 2011-06-01 integer(3pm)