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[QUOTE="Walter Roberson, post: 2453144"]
Unfortunately you did not quote any of the original task.

In C, the ^ operator is "Exclusive OR". In your description of
the original task, I would be surprised if your use of ^
did not indicate exponentiation there.

In C, 256 to the power
of 0 is 1
of 1 is 1<<8
of 2 is 1<<16
of 3 is 1<<24
of 4 is 1<<32
of 5 is 1<<40

On most systems, 1<<32 is bigger than an unsigned long will hold.
C89 does not promise that anything from 1<<32 upwards is available.
C99 does provide unsigned long long for that purpose, but you
must be careful to avoid accidently working in narrower types
in an intermediate stage.

You do not actually need to use the multiplications or additions
in your calculation of math64. Presuming C99, your code could instead be

math64 = (unsigned long long) origcode.item1 << 40 |
         (unsigned long long) origcode.item2 << 32 |
         (unsigned long long) origcode.item3 << 24 |
         (unsigned long long) origcode.item4 << 16 |
         (unsigned long long) origcode.item5 <<  8 |
         (unsigned long long) origcode.item6;
[/QUOTE]

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