epsilon.c running 
first double 1.0e-15 greater than double epsilon 
double cc = aa + bb;  dd = cc - 1.0 
aa=1  bb=1e-15  cc=1 
aa=1.000000e+00  bb=1.000000e-15  cc=1.000000e+00 
aa=1.0000000000000000e+00  bb=1.0000000000000001e-15  cc=1.0000000000000011e+00 
dd=1.11022e-15  dd=1.110223e-15  dd=1.110223024625157e-15 

next float 1.0e-7 greater than float epsilon 
float c = a + b;  d = c - 1.0 
a=1  b=1e-07  c=1 
a=1.000000e+00  b=1.000000e-07  c=1.000000e+00 
a=1.000000000000000e+00  b=1.000000011686097e-07  c=1.000000119209290e+00 
d=1.19209e-07  d=1.192093e-07  d=1.192092895507812e-07 

then double 1.0e-16 smaller than double epsilon 
double cc = aa + bb;  dd = cc - 1.0 
aa=1  bb=1e-16  cc=1 
aa=1.000000e+00  bb=1.000000e-16  cc=1.000000e+00 
aa=1.0000000000000000e+00  bb=9.9999999999999998e-17  cc=1.0000000000000000e+00 
dd=0  dd=0.000000e+00  dd=0.000000000000000e+00 
note dd = 0.0 

then float 1.0e-8 smaller than float epsilon 
float c = a + b;  d = c - 1.0 
a=1  b=1e-08  c=1 
a=1.000000e+00  b=1.000000e-08  c=1.000000e+00 
a=1.000000000000000e+00  b=9.999999939225290e-09  c=1.000000000000000e+00 
d=0  d=0.000000e+00  d=0.000000000000000e+00 
note d = 0.0 

epsilon.c finished