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What is the scope of `fesetround()`?

I learned that fesetround can be used to control FP rounding rule.

I wonder what is scope of the function? say, is it local to the very source file? or translation unit? how about thread?

Any insight will be greatly appreciated.

Solution

  • As you can see in the Floating-point environment reference:

    The floating-point environment is the set of floating-point status flags and control modes supported by the implementation. It is thread-local, each thread inherits the initial state of its floating-point environment from the parent thread.

    (emphasis is mine)

    This applies to several floating point functions which are listed there, including fesetround.

    As @TedLyngmo commented it is similarly specified in the standard (see article 7.6.3):

    The dynamic floating-point environment has thread storage duration.

    (emphasis is mine)

    I.e. the scope is the current thread.