Difference between revisions of "Floating Point Gotchas"
(Created page with "see forum discussion here: http://forum.dlang.org/post/oxadmevgkefklttnbbpi@forum.dlang.org Floating point comparisons should be undertaken with care, because decimal numbers...") |
|||
| (One intermediate revision by one other user not shown) | |||
| Line 1: | Line 1: | ||
| − | + | Floating point comparisons should be undertaken with care, because decimal numbers cannot be exactly represented using float or double. | |
| − | |||
| − | Floating point comparisons should be undertaken with care, because decimal numbers cannot be exactly represented using float or double. | ||
| − | |||
| − | |||
| − | |||
| − | |||
One should therefore in most cases use [http://dlang.org/library/std/math/feqrel.html std.math.feqrel] and or [http://dlang.org/phobos/std_math.html#.approxEqual std.math.approxEqual] instead of checking for simple equality. | One should therefore in most cases use [http://dlang.org/library/std/math/feqrel.html std.math.feqrel] and or [http://dlang.org/phobos/std_math.html#.approxEqual std.math.approxEqual] instead of checking for simple equality. | ||
| Line 11: | Line 5: | ||
These functions may be passed as a predicate to the std.algorithm library in Phobos when for example doing a search for a specific floating point value: | These functions may be passed as a predicate to the std.algorithm library in Phobos when for example doing a search for a specific floating point value: | ||
| + | void main() @safe { | ||
| + | import std.stdio, std.range, std.algorithm, std.math; | ||
| + | |||
| + | immutable float oneDegree = (PI / 180.0f); | ||
| + | immutable float first = -(oneDegree * 10.0f); | ||
| + | immutable float second = (oneDegree * 10.0f); | ||
| + | immutable float step = 0.000001f; | ||
| + | immutable float[] r = iota(first, second, step).array; | ||
| + | |||
| + | //r.writeln; | ||
| + | |||
| + | immutable float item = 0.174531f; | ||
| + | r.canFind!q{ feqrel(cast()a, cast()b) >= 21 }(item).writeln; | ||
| + | } | ||
| − | + | == See also == | |
| − | + | * [http://forum.dlang.org/post/oxadmevgkefklttnbbpi@forum.dlang.org Forum discussion] | |
| − | + | * [http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html Classic reference on this topic] | |
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | + | [[Category:Tutorials]] | |
| − | |||
| − | |||
Revision as of 18:54, 8 September 2015
Floating point comparisons should be undertaken with care, because decimal numbers cannot be exactly represented using float or double.
One should therefore in most cases use std.math.feqrel and or std.math.approxEqual instead of checking for simple equality.
These functions may be passed as a predicate to the std.algorithm library in Phobos when for example doing a search for a specific floating point value:
void main() @safe {
import std.stdio, std.range, std.algorithm, std.math;
immutable float oneDegree = (PI / 180.0f);
immutable float first = -(oneDegree * 10.0f);
immutable float second = (oneDegree * 10.0f);
immutable float step = 0.000001f;
immutable float[] r = iota(first, second, step).array;
//r.writeln;
immutable float item = 0.174531f;
r.canFind!q{ feqrel(cast()a, cast()b) >= 21 }(item).writeln;
}
