docs: add BitStr zero-copy view to README, bump to 0.4.3

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bit-string"
-version = "0.4.2"
+version = "0.4.3"
 edition = "2024"
 description = "A compact owned bit string type with editing, matching, and bitwise operations."
 readme = "README.md"

README.md

@@ -6,18 +6,28 @@
 [![CodSpeed](https://img.shields.io/endpoint?url=https://codspeed.io/badge.json)](https://codspeed.io/gh/jcfangc/bit-string)
 [![Coverage](https://codecov.io/gh/jcfangc/bit-string/branch/main/graph/badge.svg)](https://codecov.io/gh/jcfangc/bit-string)
 
-A `no_std` Rust crate providing a compact owned bit string type with construction, editing, matching, and bitwise operations.
+A `no_std` Rust crate providing a compact owned bit string type and a zero-copy view, with construction, editing, matching, comparison, hashing, and bitwise operations.
 
-The core type is `BitString`. Bits are packed into `Box<[u64]>` with unused high bits in the last word always zero (masked after every mutation).
+The two core types mirror the `String`/`&str` relationship:
+
+| Type | Role | Size | `Copy` |
+|------|------|------|--------|
+| `BitString` | Owned bit string, backed by `Box<[u64]>` | 4×usize | No |
+| `BitStr<'bs>` | Zero-copy borrowed view of a `BitString` or subrange | 3×usize (24 bytes) | **Yes** |
+
+Bits are packed little-endian into `u64` words. Unused high bits in the last word are always zero — enforced after every mutation on `BitString` and never observable through `BitStr`.
 
 ## Features
 
 - **Construction**: `new`, `zeros`, `repeat`, `from_bool_iter`, `from_words`, `try_from(&str)`
+- **Zero-copy view**: `BitStr<'bs>` — 24-byte `Copy` type returned by `as_bit_str()`, `slice()`, `slice_from()`, `slice_until()`
+- **Conversion**: `to_bit_string()` — copies a `BitStr` view into an owned `BitString`
 - **Bitwise ops**: `and`, `or`, `xor`, `not`, `shl`, `shr` (each with `_assign` and `_into` variants)
 - **Bit counting**: `count_ones`, `count_zeros`
 - **Editing**: `push`, `pop`, `insert`, `remove`, `set`, `extend`, `truncate`, `slice`, `split_off`, `replace_interval`, `retain`, `push_bit_string`, `insert_bit_string`
 - **Matching**: `starts_with`, `ends_with`, `contains`, `find`, `rfind`, `strip_prefix`, `strip_suffix`
-- **Access**: `get`, `len`, `is_empty`, `as_words`, `get_chunk`, `to_string`, `iter`
+- **Comparison & hashing**: `PartialEq`, `Eq`, `PartialOrd`, `Ord`, `Hash` for both `BitStr` and `BitString` — lexicographic comparison with SIMD acceleration
+- **Access**: `get`, `first`, `last`, `get_chunk`, `len`/`bit_len`, `is_empty`, `words`, `iter`
 
 ### SIMD backends
 
@@ -40,10 +50,25 @@ use bit_string::BitString;
 let a = BitString::try_from("1010").unwrap();
 let b = BitString::try_from("1100").unwrap();
 
+// Bitwise operations
 assert_eq!(a.and(&b).unwrap().to_string(), "1000");
 assert_eq!(a.or(&b).unwrap().to_string(),  "1110");
 assert_eq!((!a).to_string(),              "0101");
 assert_eq!(a.count_ones(), 2);
+
+// Zero-copy views via BitStr
+let view = a.as_bit_str();              // &BitString → BitStr
+let sub = view.slice_from(1);           // "010"
+assert!(sub.starts_with(&BitString::try_from("01").unwrap().as_bit_str()));
+assert_eq!(sub.count_ones(), 1);
+
+// Comparison
+use core::cmp::Ordering;
+assert_eq!(a.cmp(&b), Ordering::Less);  // "1010" < "1100"
+
+// Convert back to owned
+let owned = sub.to_bit_string();
+assert_eq!(owned.to_string(), "010");
 ```
 
 ## Benchmarks