On Tue, Jun 22, 2021 at 11:42 AM Richard Sandiford <richard.sandif...@arm.com> wrote:
> >> Well, the pattern is called addsub in the x86 world because highpart > >> does add and lowpart does sub. In left-to-right writing systems > >> highpart comes before lowpart, so you have addsub. > > > > The other targets mentioned do not seem to agree but I can live > > with that, thus I'll change back to addsub. > > FWIW, subadd sounds clearer to me too. It seems surprising to put > imaginary before real when interpreting something as complex, for example. > > Putting the highpart first feels especially odd on an LE system like x86… The XMM vector is documented left to right with MSB at the left (c.f. most significant *DIGIT* of the number at the left) xmm[MSB] .... xmm[LSB] so, looking at x86 ADDSUBPD insn documentation: xmm2[127:64] xmm2[63:0] ( + -) xmm1[127:64] xmm1[63:0] (=) xmm1[127:64] holds ADD xmm1[63:0] holds SUB xmm1[127:64] xmm1 [63:0] ADD SUB Uros.
