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Will be there an i87 inside? With 80bits registers?
by Iwan-Zotow 3y ago
Will be there an i87 inside? With 80bits registers?
- Veliladon 3y agoYes. It'll still be there. The only difference will be that you won't be able to do stuff that CR0 can control like disabling the FPU for whatever reason.
- monocasa 3y agoYou'll still be able to do that too. X87 (and MMX using the same register file) is still fully visible to 64 bit code.
- allenrb 3y agoIt looks like they’re keeping x87 support, which feels like a missed opportunity. Does any modern compiler generate these instructions? Stripping out x87 and the associated 80 bit registers, weird modes, etc would seem right in line with this effort. If someone really needs x87 support, trap those instructions and emulate in kernel. Nothing with truly high performance requirements will be using them. Intel could even provide the code.
- jcranmer 3y agoI suspect the main thing keeping x87 support is that 32-bit ABIs for x86 still use it, just for returning floats and doubles from functions, which makes trap-and-emulate not an effective solution.
- addaon 3y agoThere's still no replacement for high precision long doubles on x86; 128 bit float support seems unlikely, and double-double has not caught on. Sometimes 64 bits just ain't enough.