[cfenv.thread]

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]

A separate floating-point environment is maintained for each thread.

Each function accesses the environment corresponding to its calling thread.