Experimental Physics and
Industrial Control System

Dirk Zimoch via Core-talk <[email protected]> · Wed, 02 Oct 2019 08:55:53 -0000

Maybe it is more interesting what a calc record is doing when asked to
add infinities rather than to write constant expressions that the
compiler may try to resolve at compile time.

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https://bugs.launchpad.net/bugs/1845854

Title:
  EPICS Math tests failing on Windows with MSVC

Status in EPICS Base:
  New

Bug description:
  Some epics base tests involving NaN and Inf have been failing for most
  windows MSVC builds, I have written a small test program
  https://github.com/FreddieAkeroyd/Testing/blob/master/src/mytests/inftest.cpp
  with output at https://ci.appveyor.com/project/FreddieAkeroyd/testing
  which illustrates the underlying cause.

  The general summary is that:

  VS2010, VS2017 and VS2019 are OK in all configurations
  For other Visual studio versions:
      Debug builds are often OK  
      All release builds fail.

  The failure mode is as follows (Inf shown here but applies to NaN
  too):

  Inf – Inf is evaluated correctly
  Inf + -Inf is evaluated incorrectly
  Inf + (-Inf) is evaluated correctly on VS 11.0 and 12.0, but not 14.0

  The test code is using expressions like “a + -a” with a = Inf, if it
  instead tests “a + -b” with a = b = Inf then release mode works in all
  cases. So it looks like the repeated variable name is causing an
  undesired optimisation. I feel expressions of the form “a + -b” rather
  than “a + -a” are a better reflection of what is  likely in practice,
  if that change is acceptable then I would be happy to submit a PR to
  use different variable names within binary operation tests

  Regards,

  Freddie

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System