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diff --git a/third_party/rust/base64/README.md b/third_party/rust/base64/README.md new file mode 100644 index 0000000000..7815966c30 --- /dev/null +++ b/third_party/rust/base64/README.md @@ -0,0 +1,114 @@ +[base64](https://crates.io/crates/base64) +=== + +[](https://crates.io/crates/base64) [](https://docs.rs/base64) [](https://travis-ci.org/marshallpierce/rust-base64) [](https://codecov.io/gh/marshallpierce/rust-base64) [](https://github.com/rust-secure-code/safety-dance/) + +<a href="https://www.jetbrains.com/?from=rust-base64"><img src="/icon_CLion.svg" height="40px"/></a> + +Made with CLion. Thanks to JetBrains for supporting open source! + +It's base64. What more could anyone want? + +This library's goals are to be *correct* and *fast*. It's thoroughly tested and widely used. It exposes functionality at multiple levels of abstraction so you can choose the level of convenience vs performance that you want, e.g. `decode_config_slice` decodes into an existing `&mut [u8]` and is pretty fast (2.6GiB/s for a 3 KiB input), whereas `decode_config` allocates a new `Vec<u8>` and returns it, which might be more convenient in some cases, but is slower (although still fast enough for almost any purpose) at 2.1 GiB/s. + +Example +--- + +```rust +extern crate base64; + +use base64::{encode, decode}; + +fn main() { + let a = b"hello world"; + let b = "aGVsbG8gd29ybGQ="; + + assert_eq!(encode(a), b); + assert_eq!(a, &decode(b).unwrap()[..]); +} +``` + +See the [docs](https://docs.rs/base64) for all the details. + +Rust version compatibility +--- + +The minimum required Rust version is 1.34.0. + +Developing +--- + +Benchmarks are in `benches/`. Running them requires nightly rust, but `rustup` makes it easy: + +```bash +rustup run nightly cargo bench +``` + +Decoding is aided by some pre-calculated tables, which are generated by: + +```bash +cargo run --example make_tables > src/tables.rs.tmp && mv src/tables.rs.tmp src/tables.rs +``` + +no_std +--- + +This crate supports no_std. By default the crate targets std via the `std` feature. You can deactivate the `default-features` to target core instead. In that case you lose out on all the functionality revolving around `std::io`, `std::error::Error` and heap allocations. There is an additional `alloc` feature that you can activate to bring back the support for heap allocations. + +Profiling +--- + +On Linux, you can use [perf](https://perf.wiki.kernel.org/index.php/Main_Page) for profiling. Then compile the benchmarks with `rustup nightly run cargo bench --no-run`. + +Run the benchmark binary with `perf` (shown here filtering to one particular benchmark, which will make the results easier to read). `perf` is only available to the root user on most systems as it fiddles with event counters in your CPU, so use `sudo`. We need to run the actual benchmark binary, hence the path into `target`. You can see the actual full path with `rustup run nightly cargo bench -v`; it will print out the commands it runs. If you use the exact path that `bench` outputs, make sure you get the one that's for the benchmarks, not the tests. You may also want to `cargo clean` so you have only one `benchmarks-` binary (they tend to accumulate). + +```bash +sudo perf record target/release/deps/benchmarks-* --bench decode_10mib_reuse +``` + +Then analyze the results, again with perf: + +```bash +sudo perf annotate -l +``` + +You'll see a bunch of interleaved rust source and assembly like this. The section with `lib.rs:327` is telling us that 4.02% of samples saw the `movzbl` aka bit shift as the active instruction. However, this percentage is not as exact as it seems due to a phenomenon called *skid*. Basically, a consequence of how fancy modern CPUs are is that this sort of instruction profiling is inherently inaccurate, especially in branch-heavy code. + +```text + lib.rs:322 0.70 : 10698: mov %rdi,%rax + 2.82 : 1069b: shr $0x38,%rax + : if morsel == decode_tables::INVALID_VALUE { + : bad_byte_index = input_index; + : break; + : }; + : accum = (morsel as u64) << 58; + lib.rs:327 4.02 : 1069f: movzbl (%r9,%rax,1),%r15d + : // fast loop of 8 bytes at a time + : while input_index < length_of_full_chunks { + : let mut accum: u64; + : + : let input_chunk = BigEndian::read_u64(&input_bytes[input_index..(input_index + 8)]); + : morsel = decode_table[(input_chunk >> 56) as usize]; + lib.rs:322 3.68 : 106a4: cmp $0xff,%r15 + : if morsel == decode_tables::INVALID_VALUE { + 0.00 : 106ab: je 1090e <base64::decode_config_buf::hbf68a45fefa299c1+0x46e> +``` + + +Fuzzing +--- + +This uses [cargo-fuzz](https://github.com/rust-fuzz/cargo-fuzz). See `fuzz/fuzzers` for the available fuzzing scripts. To run, use an invocation like these: + +```bash +cargo +nightly fuzz run roundtrip +cargo +nightly fuzz run roundtrip_no_pad +cargo +nightly fuzz run roundtrip_random_config -- -max_len=10240 +cargo +nightly fuzz run decode_random +``` + + +License +--- + +This project is dual-licensed under MIT and Apache 2.0. |