> I was giving an historic rationale for why x87 didn't change to use SSE. When stated as "why x87 didn't change to use SSE" the question is like asking "why a

> I was giving an historic rationale for why x87 didn't change to use SSE. When stated as "why x87 didn't change to use SSE" the question is like asking "why a dog didn't change to use a cat" as both x87 and SSE are the instruction sets, from the start differently defined, and given that, one can't "use" another. The original question, however, referred to fsin instruction of x87 instruction set, but also reflected somewhat of confusion, as neither SSE nor SSE2 had ever an instruction to calculate sine. And the answer in which you apparently gave a "historic rationale" had incorrect statements, the correction of which is: 1) x87 didn't "have 32 and 64 bits", the x87 was ambitiously designed to do 80-bit precise calculations with the shorter results as the additional modes. 2) SSE was 32-bit only, but SSE2 added 64-bit instructions too. Still, x87 could not "use the implementation" of fsin from SSE2 as SSE2 doesn't provide the sine function. Finally, if the question was why wasn't the "fsin" ever improved, please see the other responses here, including mine.