[Issue 18734] bitnum parameter of core.bitop.bt should be signed

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18734

--- Comment #2 from ag0aep6g <ag0aep6g at gmail.com> ---
(In reply to uplink.coder from comment #1)
> DMD does not recognize bodies only function signatures.
> So change it all you like :) it's only going to be used on systems where the
> intrinsic can't work.

core.bitop.bt is not an intrinsic. The expression in the body is recognized by
the optimizer.

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