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The floating-point status word in a multithreaded environment

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 variants are selected by default. The armclang command-line option -ffast-math selects the other variants.