The ending value may not be exact due to floating point arithmetic.

[mbostock]

In many cases in this library we use the interpolated value

a + (b - a) * t

This can return a value not equal to b when t = 1. If we want to guarantee that the exact value b is returned for t = 1, we should instead use the formula

a * (1 - t) + b * t

[mbostock]

@Fil Should we take a crack at this?

[Fil]

I was under the impression that this was a kind of optimisation (doing substractions once—probably ultra negligible). Also, the substraction was a nuisance when working with Uint32 numbers…

In any case, I think having exact ends is desirable.