Stephen Canon 35db40c9f9 Make BinaryInteger._binaryLogarithm() return Int instead of Self (#18219) ...

Returning `Self` was probably a hack from when shifts were required to be homogenous and we didn't have good generic inits between integer types. Returning Int is more natural, because:

1. Dimensional analysis says that we shouldn't expect the logarithm to have the same type.
2. Int is guaranteed to be able to represent any object size, and BinaryInteger does not admit sparse representations, so the logarithm of the value cannot exceed allocated storage size.
3. Every single use case in the stdlib and tests is either unchanged or simplified by this change.

2018-07-25 14:04:32 -04:00

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