get_pi.c using double and math.h atan 
pi=24*atan(b2) b2=0.131652, b1=0.267949 
b2**10=1.5642e-09, b2**20=2.44671e-18 
    Pi= 3.1415926535897932384626433832795028841971 
get_pi= 3.14159265358980333 
 pi-Pi= 0.00000000000001021