From: Su Zhang <zhangsu@...>
Date: 2011-04-15T03:01:42+09:00
Subject: Re: Exclusive float range, Range#step result in counterintuitive result

This looks like a bug to me.

(The problem exists as of 1.9.2-p180.)

In <range.c>, `range_step' is the implementation of Range#step. It calls 
`ruby_float_step', which is implemented in <numeric.c>, to handle float 
stepping.

The call looks like this:

    else if (ruby_float_step(b, e, step, EXCL(range))) {
  /* done */
    }

The problem is that it passes the `exclude_end?' property of the range 
to `ruby_float_step', in our case it is false. Inside the implementation 
of `ruby_float_step' is something like:

      n = floor(n + err);
      if (!excl) n++;
      for (i=0; i<n; i++) {
    rb_yield(DBL2NUM(i*unit+beg));
      }

And excl is the last parameter. Clearly if the end value of the range is 
x, then the iteration only goes to floor(x)-1.

On the other hand -

p 1.step(6.3).to_a # => [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]

This works since `num_step', again implemented in <numeric.c>, 
explicitly passes a false to excl:

    else if (!ruby_float_step(from, to, step, FALSE)) {
        ...

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