> Probably doesn't fit precisely into a double.  Does strtold behave
> better?

actually both numbers can be represented exactly as IEEE double. In Maxima:

(%i1)   factor(121645100408832000);
(%o1)   2^16*3^8*5^3*7^2*11*13*17*19
(%i2)   float(log(3^8*5^3*7^2*11*13*17*19)/log(2));
(%o2)   40.75545582601886

(%i3)   factor(221645100408832000);
(%o3)   2^16*5^3*31*41*1361*15641
(%i4)   float(log(5^3*31*41*1361*15641)/log(2));
(%o4)   41.62102908434535

So the first number has 41 bits and the second 42 after removing powers of 2. 
The significand size of a double is 53 bits (including the implicit 1).

Best regards,

Michael
Intel Deutschland GmbH
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