use sqrtf and expf to prevent auto-casts to double
use sqrtf and expf to prevent auto-casts to double

fixes #139

poljere/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,takahito-tejima/OpenSubdiv-exp,jcowles/OpenSubdiv,shengfuintel/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,takahito-tejima/OpenSubdiv,anshuarya/OpenSubdiv,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,nyotis/OpenSubdiv,xldeveloper/OpenSubdiv,c64kernal/OpenSubdiv,xldeveloper/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv,shengfuintel/OpenSubdiv,anshuarya/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,jcowles/OpenSubdiv,c64kernal/OpenSubdiv,lookup1980/OpenSubdiv,lookup1980/OpenSubdiv,poljere/OpenSubdiv,c64kernal/OpenSubdiv,nyotis/OpenSubdiv,jcowles/OpenSubdiv