dherring@ll.mit.edu wrote:
On Tue, 29 Apr 2008, John Maddock wrote:
Folks I'm looking for some good names for some functions I'm on the brink of adding to Boost.Math (all in namespace boost::math::):
T nextafter(T val, T dir) T next_greater(T val) T next_less(T val)
Given the first name is fixed, this is a reasonable family of names; though dropping the underscore would increase consistency. However, there is the ambiguity whether greater/less reference zero or infinity.
Not sure what you mean there, next_greater returns a value that is strictly greater than the argument (so always moves towards positive infinity).
nextpositive() and nextnegative() might be clearer. Why does this remind me of IEEE-754 rounding modes?
T edit_distance(T a, T b)
Returns the number of floating point representations between values a and b.
So the questions are: can you think of any better names, or are these OK?
And should edit_distance return a signed or absolute value?
I'm at a loss for a better name (representation_distance seems overly verbose but interval_size might be ok), but do have a couple questions about this function's behavior.
Why is the return value templated? Shouldn't it be some fixed diff_t? I tentatively agree with the other comment that a signed distance is preferable to unsigned.
I was undecided about this: but for large intervals a std::difference_t wouldn't be large enough, for example edit_distance(0.0, 1.0) is approx 1.97753e+032. Of course if you use for intervals that stretch several orders of magnitude then you get what you deserve I guess!
Shouldn't this return the number of gaps, rather than the number of representations? Consider the following examples
float x=1.0; float y=2.0; int d=edit_distance(x, y); float z=x; for(int i=0; i<d; i++) { z=next_greater(z); } // Does y==z?
A rather long running program, but yes: edit_distance(next_less(x), x) == 1.
z=x; for(int i=0; i<d/2; i++) { z=next_greater(z); } // Does y==(x+z)/2, given the right rounding mode?
Change i<d/2 to i<2*d and yes I believe so. HTH, John.