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The floating-point status word in a multithreaded environment

Applicable to variants of the software floating-point libraries that require a status word, the floating-point status word is safe to use in a multithreaded environment, even with software floating-point.

A status word for each thread is stored in its own __user_perthread_libspace block.


In a hardware floating-point environment, the floating-point status word is stored in a Vector Floating-Point (VFP) register. In this case, your thread-switching mechanism must keep a separate copy of this register for each thread.

In Arm® Compiler 6, floating-point library variants are selected by default. For more information see the armclang command-line option -ffp-mode.

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