On Jul 17, 2020, at 11:46 AM, stes@PANDORA.BE <stes@telenet.be> wrote:

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I've noticed that in the FloatMathPlugin there is fdlibm
(freely distributable libm) :

platforms/Cross/plugins/FloatMathPlugin

This refers to the platforms/Cross/third-party/fdlibm

I wonder whether the VM shouldn't be using the system provided libm (-lm).

Perhaps for Croquet or other software that depends on FLoatMathPlugin,
see https://en.m.wikipedia.org/wiki/Croquet_Project
a special test framework could be ran in Squeak,
or perhaps as part of "./configure" configuration, to check the results,
of the underlying (system) libm, so that it provides results similar to fdlibm ?

Maybe fdlibm and libm "run bit identically" on some platforms.

This is because for Croquet the goal is to have the VM run bit identically.

Using the system provided -lm would possibly result in a smaller executable,
with less duplicated code (no overhead).

I'm no expert on libm, but perhaps the system provided libm is also faster.

What we want (I think) is either the entire vm, including the FloatMathPlugin, links against the platform’s libm, or the entire vm, including the FloatMathPlugin, links against fdlibm. I don’t see much benefit in arbitrarily mixing and matching.

So then we arrive at the above message. Is the default to link against the platform’s libm, requiring a Makefile to specify BIT_IDENTICAL_FLOATING_POINT to link against fdlibm, or is the default to link against fdlibm, requiring a Makefile to specify PLATFORM_SPECIFIC_FLOATING_POINT to link against the platform’s libm?

I agree with Marcel that the latter is preferable, by default a vm provides bit-identical floating-point, building and linking against fdlibm. For the moment we have the former.

Im not too concerned about core floating-point performance. I don’t think it dominates in our usage because we have other overheads, primarily primitive invocation and boxing/unboxing. Whereas I do think that the core execution engine should be perfectly cross-platform, and floating point is the one area I’m aware of where the platform percolates up. So I think we should make it an objective that the 6.0 release vm links against fdlibm.

What do people think?

_,,,^..^,,,_ (phone)