RISC-V doesn't support floating-point exceptions.
RISC-V Instruction Set Manual: Volume I: User-Level ISA, 11.2
Floating-Point Control and Status Register: "As allowed by the standard,
we do not support traps on floating-point exceptions in the base ISA,
but instead require explicit checks of the flags in software. We
considered adding branches controlled directly by the contents of the
floating-point accrued exception flags, but ultimately chose to omit
these instructions to keep the ISA simple."
We still need these functions, because some applications (notably Perl)
call them, but we cannot provide a meaningful implementation.
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