[ruby-core:104307] Float truncate

Hi!

A customer just noticed a weird behaviour on its app, regarding float
truncate. I know floats are wild beasts and we can have some surprises as
stated on the truncate docs as

(0.3 / 0.1).truncate
=> 2

But let me show what they found:

> 291.1.truncate(2)
 => 291.1
> 291.2.truncate(2)
 => 291.2
> 291.3.truncate(2)
 => 291.3
> 291.4.truncate(2)
 => 291.39 <------------------ here!
> 291.5.truncate(2)
 => 291.5

Notice 291.4 truncating to 2, returns 291.39! They have another number like
.3 that truncates to .2, so I just took a look on rb_float_floor and found
that 291.4 is converted to 29139.000000 after powered and sent to

floor(number * f)

and then proceeds to DBL2NUM when it returns 291.39. I advised them to use
another approach other than truncate (round don't work for them because of
the ceil/floor operation) but I'm curious if it is a known behaviour of
float truncate.

Thanks.

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>