SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Problem:
- Post-increment of loop index.
- `const` variables are not marked `const`.
- Incorrect type for loop index.
Solution:
- Pre-increment loop index.
- Mark all possible variables `const`.
- Corret type for loop index.
Problem:
- Hex digit decoding is not `constexpr`, but can be.
Solution:
- Move the body of the function to the header and decorate with
`constexpr`.
- Provide tests for run-time and compile-time evaluation.
