Hi David,
On Jul 17, 2020, at 11:46 AM, stes@PANDORA.BE stes@telenet.be wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256
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.
For context see https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/383#issuecomment-62...
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?
Regards, David Stes
Eliot _,,,^..^,,,_ (phone)