浮点乘法执行速度较慢，具体取决于C中的操作数

I am performing a stencil computation on a matrix I previously read from a file. I use two different kinds of matrices (NonZero type and Zero type). Both types share the value of the boundaries (1000 usually), whilst the rest of the elements are 0 for Zero type and 1 for NonZero type.I am performing a stencil computation on a matr