I know that the behavior of >> on signed integer can be implementation dependent (specifically, when the left operand is negative).
What about the others: ~, >>, &, ^, |?
When their operands are signed integers of built-in type (short, int, long, long long), are the results guaranteed to be the same (in terms of bit content) as if their type is unsigned?
The C89 Standard defined the behavior of left-shifting signed numbers based upon bit positions. If neither signed nor unsigned types have padding bits, the required behavior for unsigned types, combined with the requirement that positive signed types share the same representation as unsigned types, would imply that the sign bit is immediately to the left of the most significant value bit.
This, in C89, -1<<1 would be -2 on two's-complement implementations which don't have padding bits and -3 on ones'-complement implementations which don't have padding bits. If there are any sign-magnitude implementations without padding bits, -1<<1 would equal 2 on those.
The C99 Standard changed left-shifts of negative values to Undefined Behavior, but nothing in the rationale gives any clue as to why (or even mentions the change at all). The behavior required by C89 may have been less than ideal in some ones'-complement implementations, and so it would made sense to allow those implementations the freedom to select something better. I've seen no evidence to suggest that the authors of the Standard didn't intended that quality two's-complement implementations should continue to provide the same behavior mandated by C89, but unfortunately they didn't actually say so.
