XSfvfbfexp16e, XSfvfexp16e, and XSfvfexp32e are SiFive's vector
exponential instruction extensions of BFloat16, F16, and F32,
respectively. Spec:
https://www.sifive.com/document-file/exponential-function-instruction-xsfvfexp32e-xsfvf
XSfvfexpa and XSfvfexpa64e are SiFive's vector exponential approximation
instruction extensions where the former supports F16 and F32 and the
latter covers F64. These instructions approximate 2 raised to a
fractional power. Spec:
https://www.sifive.com/document-file/exponential-approximation-instruction-xsfvfexpa-ex
This patch adds their corresponding features and MC supports.
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Co-authored-by: Jesse Huang <jesse.huang@sifive.com>
Co-authored-by: Craig Topper <craig.topper@sifive.com>
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