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# Bit-wise `memset`
This fills a region of memory with a bit value. It is equivalent to using
`memset` with only `!0` or `0`, masked appropriately for the region edges.
## Original
[`ptr::write_bytes`](core::ptr::write_bytes)
## Safety
Because this performs a dereference of memory, it inherits the original
`ptr::write_bytes`’ requirements:
- `dst` must be valid to write
- `dst` must be properly aligned. This is an invariant of the `BitPtr` type as
well as of the memory access.
Additionally, `dst` must point to an initialized value of `T`. Integers cannot
be initialized one bit at a time.
## Behavior
This function does not specify an implementation. You should assume the worst
case (`O(n)` read/modify/write of each bit). The [`BitSlice::fill`][0] method
will have equal or better performance.
## Examples
```rust
use bitvec::prelude::*;
use bitvec::ptr as bv_ptr;
let mut data = 0u8;
let ptr = BitPtr::<_, _, Lsb0>::from_mut(&mut data);
unsafe {
bv_ptr::write_bits(ptr.add(1), true, 5);
}
assert_eq!(data, 0b0011_1110);
```
[0]: crate::slice::BitSlice::fill
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