SBCL Internals : PENTIUM-STYLE-FYL2XP1

SBCL Internals
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:PENTIUM-STYLE-FYL2XP1 is a useful value for x86 SBCLs to have on SB-C:*BACKEND-SUBFEATURES*?; it enables the use of the %flog1p-pentium? VOP rather than the %flog1p? VOP, which is a few instructions longer.

Health warnings:

This information is only accurate as of 0.7pre57; this mechanism and/or interface may change.
You will only see a speedup in ATANH and LOG (the two functions in the core that use SB-KERNEL:%LOG1P?) if :PENTIUM-STYLE-FYL2XP1 is on the *BACKEND-SUBFEATURES*? list at cross-compile-time.

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