My method assigns a decimal power of two from the table directly to a variable. Your method assigns a power of two indirectly through knowledge of the underlying binary representation (two’s complement) and bit shifting operations. Both methods work: mine uses the “2ⁿ” column, and yours uses the “n” column. I would think it’s just a matter of personal preference as to which method you choose.

As for performance, there’s no difference. Both should be resolved at compile time. For example, under Visual C++, both resolve to these two assembler statements:

00419B4E  mov         dword ptr [po2],0
00419B55  mov         dword ptr [ebp-8],80000000h

Use the left shift operator (<<) instead, like
unsigned long long po2 = 1ULL<<63;