[PATCH] math: Update tanh from CORE-MATH (revision cf237fa0)

[Paul Zimmermann]

       Hi,

as a CORE-MATH developer, I have to say the main point of this patch is to fix an
incorrect rounding in some corner cases, for example x=0x1.a0112a16e9318p+1 is
incorrectly rounded with rounding upward and no fma contraction.

Paul