GBE: improve precision of expm1
GBE: improve precision of expm1

Signed-off-by: Lv Meng <2df664ee4255226675c7b29e26307ac8da3842dc@intel.com>
Tested-by: "Yang, Rong R" <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

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