In order to reduce rounding problems from calculations, FPU stack
registers for x86 architectures contain values stored in an
80-bit extended precision format.
As a result, reading and writing to these registers requires
specific handling.
This update brings the Ruby bindings in line with the Python
bindings by supporting reading and writing the FPU stack registers
using 2-element arrays: [mantissa, exponent]
The mantissa array element contains the first 64 bits of the FPU
stack register.
The exponent array element contains the last 16 bits of the FPU
stack register.
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