At least according to godbolt.org, the three routines don't get folded into the same assembly code. What's (somewhat) interesting is that gcc and clang create different addressing modes for the accesses, so it might be worth to switch between compilers and compiler versions if calculating the check digits was material to the program operation.

In reply to Re^9: Faster Luhn Check Digit Calculation? by Corion
in thread Faster Luhn Check Digit Calculation? by kschwab

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