Christopher Haster 4f08424b51 Added software implementations of bitwise instructions ...

This helps significantly with supporting different compilers. Intrinsics for
different compilers can be added as they are found.

Note that for ARMCC, __builtin_ctz is not used. This was the result of a
strange issue where ARMCC only emits __builtin_ctz when passed the
--gnu flag, but __builtin_clz and __builtin_popcount are always emitted.
This isn't a big problem since the ARM instruction set doesn't have a
ctz instruction, and the npw2 based implementation is one of the most
efficient.

Also note that for littefs's purposes, we consider ctz(0) to be
undefined. This lets us save a branch in the software lfs_ctz
implementation.

2018-02-19 01:39:04 -06:00

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