问题
I'm trying to understand some code in the D language runtime. It seems like there are separate functions for the following two things:
array1[] += scalar * array2[];
array1[] += array2[] * scalar;
Why can't these be done with one function? I thought multiplication was commutative even in inexact floating-point arithmetic.
回答1:
I know nothing about the D language, but I'll happily answer the question in your title:
Is multiplication always commutative in inexact floating point arithmetic?
Up to the "payload" of NaN values, yes. IEEE-754 floating-point multiplication is commutative (and so is addition). If you don't know what the payload of a NaN is, don't worry about it.
回答2:
I guess the difference is just in the function prototypes - one is (double, double[]) and the other is (double[], double). But the result should be the same either way.
来源：https://stackoverflow.com/questions/5007400/is-multiplication-always-commutative-in-inexact-floating-point-arithmetic