28 Numerics library [numerics]

28.3 The floating-point environment [cfenv]

28.3.2 Threads [cfenv.thread]

1
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The floating-point environment has thread storage duration.
The initial state for a thread's floating-point environment is the state of the floating-point environment of the thread that constructs the corresponding thread object ([thread.thread.class]) or jthread object ([thread.jthread.class]) at the time it constructed the object.
[Note 1: 
That is, the child thread gets the floating-point state of the parent thread at the time of the child's creation.
— end note]
2
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A separate floating-point environment is maintained for each thread.
Each function accesses the environment corresponding to its calling thread.