simd - "fixing up" float 是什么意思？

Question

我正在查看 AVX-512 中的指令集，并注意到一组 fixup 指令。一些examples :

_mm512_fixupimm_pd, 
_mm512_mask_fixupimm_pd, 
_mm512_maskz_fixupimm_pd

_mm512_fixupimm_round_pd, 
_mm512_mask_fixupimm_round_pd, 
_mm512_maskz_fixupimm_round_pd

这里的“修复”是什么意思？

Answer 1

这是一个很好的问题。英特尔的答案(我的粗体)在这里:

This instruction is specifically intended for use in fixing up the results of arithmetic calculations involving one source so that they match the spec, although it is generally useful for fixing up the results of multiple-instruction sequences to reflect special-number inputs. For example, consider rcp(0). Input 0 to rcp, and you should get INF according to the DX10 spec. However, evaluating rcp via Newton-Raphson, where x=approx(1/0), yields an incorrect result. To deal with this, VFIXUPIMMPS can be used after the N-R reciprocal sequence to set the result to the correct value (i.e. INF when the input is 0).

在以下位置查找 VFIXUPIMMPD:

https://software.intel.com/sites/default/files/managed/0d/53/319433-022.pdf