[ER] Basic bit twiddling methods

[leonardo-m]

A simple enhancement request. I think in line with the idea of Rust design to give low level control, to offer an ergonomic API that reduces the chances for bugs while keeping code efficient, and at the same time avoiding too many special operators, I think Rust stdlib could add few simple functions to work on bits of integral values (u8, i8, ...etc, usize, isize and char):

x.set_bit(7);
x.set_bit(1 ..= 3);
x.reset_bit(7);
x.reset_bit(1 .. 5);
x.invert_bit(7);
x.invert_bit(2 ..);
if x.is_bit_set(7) {} // For simplicity this accepts only single indexes.
if x.is_bit_reset(7) {}

Such functions can be implemented in user level code, in just a handful of lines, but they are twiddly and it's boring to implement them many times (especially the interval ones), so having them in the stdlib saves bugs, time and allows to focus on more interesting code :-)

[ivan770]

I'm not sure if std really needs those methods, but if you think so, you could file an RFC in https://github.com/rust-lang/rfcs.

[thomcc]

It would be nice to have these on AtomicInts too, since x86/x86_64 has dedicated instructions for them, which LLVM won't figure out that it can use: https://bugs.llvm.org/show_bug.cgi?id=37974

That said I've just been using inline asm for them, and since they're a performance thing, that's enough.

[trevyn]

Is this something that exists in any crates?

[leonardo-m]

Is this something that exists in any crates?

A better question seems to me: how many times this functionality is re-implemented in crates? I suspect many times.

[leonardo-m]

For related ideas see also:
http://cseweb.ucsd.edu/~rjhala/papers/bit_level_types_for_high_level_reasoning.pdf

Another (const generics) method could be:

x.get_bits::<2 .. 12>()

That means:

p & 0xFFC

[leonardo-m]

See also:
rust-lang/stdarch#703

[leonardo-m]

See also:
http://docs.myhdl.org/en/stable/manual/hwtypes.html

This suggests that slicing could also be used for copying (and perhaps assignment).

x.set_bits(y.get_bits(1 .. 5));

[leonardo-m]

See also:
https://ruby-doc.org/core-2.7.0/Integer.html#method-i-5B-5D