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README.OpenSource
1 [ 2 { 3 "Name": "memchr", 4 "License": "MIT", 5 "License File": "LICENSE-MIT", 6 "Version Number": "2.5.0", 7 "Owner": "fangting12@huawei.com", 8 "Upstream URL": "https://github.com/BurntSushi/memchr", 9 "Description": "A Rust library that provides support for searching for characters in memory." 10 } 11 ]
README.md
1 memchr 2 ====== 3 This library provides heavily optimized routines for string search primitives. 4 5 [](https://github.com/BurntSushi/memchr/actions) 6 [](https://crates.io/crates/memchr) 7 8 Dual-licensed under MIT or the [UNLICENSE](https://unlicense.org/). 9 10 11 ### Documentation 12 13 [https://docs.rs/memchr](https://docs.rs/memchr) 14 15 16 ### Overview 17 18 * The top-level module provides routines for searching for 1, 2 or 3 bytes 19 in the forward or reverse direction. When searching for more than one byte, 20 positions are considered a match if the byte at that position matches any 21 of the bytes. 22 * The `memmem` sub-module provides forward and reverse substring search 23 routines. 24 25 In all such cases, routines operate on `&[u8]` without regard to encoding. This 26 is exactly what you want when searching either UTF-8 or arbitrary bytes. 27 28 ### Compiling without the standard library 29 30 memchr links to the standard library by default, but you can disable the 31 `std` feature if you want to use it in a `#![no_std]` crate: 32 33 ```toml 34 [dependencies] 35 memchr = { version = "2", default-features = false } 36 ``` 37 38 On x86 platforms, when the `std` feature is disabled, the SSE2 accelerated 39 implementations will be used. When `std` is enabled, AVX accelerated 40 implementations will be used if the CPU is determined to support it at runtime. 41 42 ### Using libc 43 44 `memchr` is a routine that is part of libc, although this crate does not use 45 libc by default. Instead, it uses its own routines, which are either vectorized 46 or generic fallback routines. In general, these should be competitive with 47 what's in libc, although this has not been tested for all architectures. If 48 using `memchr` from libc is desirable and a vectorized routine is not otherwise 49 available in this crate, then enabling the `libc` feature will use libc's 50 version of `memchr`. 51 52 The rest of the functions in this crate, e.g., `memchr2` or `memrchr3` and the 53 substring search routines, will always use the implementations in this crate. 54 One exception to this is `memrchr`, which is an extension in `libc` found on 55 Linux. On Linux, `memrchr` is used in precisely the same scenario as `memchr`, 56 as described above. 57 58 59 ### Minimum Rust version policy 60 61 This crate's minimum supported `rustc` version is `1.41.1`. 62 63 The current policy is that the minimum Rust version required to use this crate 64 can be increased in minor version updates. For example, if `crate 1.0` requires 65 Rust 1.20.0, then `crate 1.0.z` for all values of `z` will also require Rust 66 1.20.0 or newer. However, `crate 1.y` for `y > 0` may require a newer minimum 67 version of Rust. 68 69 In general, this crate will be conservative with respect to the minimum 70 supported version of Rust. 71 72 73 ### Testing strategy 74 75 Given the complexity of the code in this crate, along with the pervasive use 76 of `unsafe`, this crate has an extensive testing strategy. It combines multiple 77 approaches: 78 79 * Hand-written tests. 80 * Exhaustive-style testing meant to exercise all possible branching and offset 81 calculations. 82 * Property based testing through [`quickcheck`](https://github.com/BurntSushi/quickcheck). 83 * Fuzz testing through [`cargo fuzz`](https://github.com/rust-fuzz/cargo-fuzz). 84 * A huge suite of benchmarks that are also run as tests. Benchmarks always 85 confirm that the expected result occurs. 86 87 Improvements to the testing infrastructure are very welcome. 88 89 90 ### Algorithms used 91 92 At time of writing, this crate's implementation of substring search actually 93 has a few different algorithms to choose from depending on the situation. 94 95 * For very small haystacks, 96 [Rabin-Karp](https://en.wikipedia.org/wiki/Rabin%E2%80%93Karp_algorithm) 97 is used to reduce latency. Rabin-Karp has very small overhead and can often 98 complete before other searchers have even been constructed. 99 * For small needles, a variant of the 100 ["Generic SIMD"](http://0x80.pl/articles/simd-strfind.html#algorithm-1-generic-simd) 101 algorithm is used. Instead of using the first and last bytes, a heuristic is 102 used to select bytes based on a background distribution of byte frequencies. 103 * In all other cases, 104 [Two-Way](https://en.wikipedia.org/wiki/Two-way_string-matching_algorithm) 105 is used. If possible, a prefilter based on the "Generic SIMD" algorithm 106 linked above is used to find candidates quickly. A dynamic heuristic is used 107 to detect if the prefilter is ineffective, and if so, disables it. 108