lib: add Float::is_approx to compare floats

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/kernel.nit b/lib/standard/kernel.nit
index 2e9c9ae..2f2df4b 100644 (file)
--- a/lib/standard/kernel.nit
+++ b/lib/standard/kernel.nit
@@ -331,6 +331,21 @@ universal Float
                end
        end
 
+       # Compare float numbers with a given precision.
+       #
+       # Because of the loss of precision in floating numbers,
+       # the `==` method is often not the best way to compare them.
+       #
+       # ~~~
+       # assert 0.01.is_approx(0.02, 0.1)   == true
+       # assert 0.01.is_approx(0.02, 0.001) == false
+       # ~~~
+       fun is_approx(other, precision: Float): Bool
+       do
+               assert precision >= 0.0
+               return self <= other + precision and self >= other - precision
+       end
+
        redef fun max(other)
        do
                if self < other then