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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "integer 3" |
| 132 | .TH integer 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | integer \- Perl pragma to use integer arithmetic instead of floating point |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | .Vb 3 |
| 138 | \& use integer; |
| 139 | \& $x = 10/3; |
| 140 | \& # $x is now 3, not 3.33333333333333333 |
| 141 | .Ve |
| 142 | .SH "DESCRIPTION" |
| 143 | .IX Header "DESCRIPTION" |
| 144 | This tells the compiler to use integer operations from here to the end |
| 145 | of the enclosing \s-1BLOCK\s0. On many machines, this doesn't matter a great |
| 146 | deal for most computations, but on those without floating point |
| 147 | hardware, it can make a big difference in performance. |
| 148 | .PP |
| 149 | Note that this only affects how most of the arithmetic and relational |
| 150 | \&\fBoperators\fR handle their operands and results, and \fBnot\fR how all |
| 151 | numbers everywhere are treated. Specifically, \f(CW\*(C`use integer;\*(C'\fR has the |
| 152 | effect that before computing the results of the arithmetic operators |
| 153 | (+, \-, *, /, %, +=, \-=, *=, /=, %=, and unary minus), the comparison |
| 154 | operators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &, |
| 155 | ^, <<, >>, |=, &=, ^=, <<=, >>=), the operands have their fractional |
| 156 | portions truncated (or floored), and the result will have its |
| 157 | fractional portion truncated as well. In addition, the range of |
| 158 | operands and results is restricted to that of familiar two's complement |
| 159 | integers, i.e., \-(2**31) .. (2**31\-1) on 32\-bit architectures, and |
| 160 | \&\-(2**63) .. (2**63\-1) on 64\-bit architectures. For example, this code |
| 161 | .PP |
| 162 | .Vb 7 |
| 163 | \& use integer; |
| 164 | \& $x = 5.8; |
| 165 | \& $y = 2.5; |
| 166 | \& $z = 2.7; |
| 167 | \& $a = 2**31 - 1; # Largest positive integer on 32-bit machines |
| 168 | \& $, = ", "; |
| 169 | \& print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1; |
| 170 | .Ve |
| 171 | .PP |
| 172 | will print: 5.8, \-5, 7, 3, 2, 10, 1, 2147483647, \-2147483648 |
| 173 | .PP |
| 174 | Note that \f(CW$x\fR is still printed as having its true non-integer value of |
| 175 | 5.8 since it wasn't operated on. And note too the wrap-around from the |
| 176 | largest positive integer to the largest negative one. Also, arguments |
| 177 | passed to functions and the values returned by them are \fBnot\fR affected |
| 178 | by \f(CW\*(C`use integer;\*(C'\fR. E.g., |
| 179 | .PP |
| 180 | .Vb 3 |
| 181 | \& srand(1.5); |
| 182 | \& $, = ", "; |
| 183 | \& print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10); |
| 184 | .Ve |
| 185 | .PP |
| 186 | will give the same result with or without \f(CW\*(C`use integer;\*(C'\fR The power |
| 187 | operator \f(CW\*(C`**\*(C'\fR is also not affected, so that 2 ** .5 is always the |
| 188 | square root of 2. Now, it so happens that the pre\- and post\- increment |
| 189 | and decrement operators, ++ and \-\-, are not affected by \f(CW\*(C`use integer;\*(C'\fR |
| 190 | either. Some may rightly consider this to be a bug \*(-- but at least it's |
| 191 | a long-standing one. |
| 192 | .PP |
| 193 | Finally, \f(CW\*(C`use integer;\*(C'\fR also has an additional affect on the bitwise |
| 194 | operators. Normally, the operands and results are treated as |
| 195 | \&\fBunsigned\fR integers, but with \f(CW\*(C`use integer;\*(C'\fR the operands and results |
| 196 | are \fBsigned\fR. This means, among other things, that ~0 is \-1, and \-2 & |
| 197 | \&\-5 is \-6. |
| 198 | .PP |
| 199 | Internally, native integer arithmetic (as provided by your C compiler) |
| 200 | is used. This means that Perl's own semantics for arithmetic |
| 201 | operations may not be preserved. One common source of trouble is the |
| 202 | modulus of negative numbers, which Perl does one way, but your hardware |
| 203 | may do another. |
| 204 | .PP |
| 205 | .Vb 4 |
| 206 | \& % perl -le 'print (4 % -3)' |
| 207 | \& -2 |
| 208 | \& % perl -Minteger -le 'print (4 % -3)' |
| 209 | \& 1 |
| 210 | .Ve |
| 211 | .PP |
| 212 | See \*(L"Pragmatic Modules\*(R" in perlmodlib, \*(L"Integer Arithmetic\*(R" in perlop |