Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 95 insertions, 0 deletions

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+# How to contribute
+
+- Pick your favorite math function from the [issue tracker].
+- Look for the C implementation of the function in the [MUSL source code][src].
+- Copy paste the C code into a Rust file in the `src/math` directory and adjust
+  `src/math/mod.rs` accordingly. Also, uncomment the corresponding trait method
+  in `src/lib.rs`.
+- Write some simple tests in your module (using `#[test]`)
+- Run `cargo test` to make sure it works
+- Run `cargo test --features musl-reference-tests` to compare your
+  implementation against musl's
+- Send us a pull request! Make sure to run `cargo fmt` on your code before
+  sending the PR. Also include "closes #42" in the PR description to close the
+  corresponding issue.
+- :tada:
+
+[issue tracker]: https://github.com/rust-lang/libm/issues
+[src]: https://git.musl-libc.org/cgit/musl/tree/src/math
+[`src/math/truncf.rs`]: https://github.com/rust-lang/libm/blob/master/src/math/truncf.rs
+
+Check [PR #65] for an example.
+
+[PR #65]: https://github.com/rust-lang/libm/pull/65
+
+## Tips and tricks
+
+- *IMPORTANT* The code in this crate will end up being used in the `core` crate so it can **not**
+  have any external dependencies (other than `core` itself).
+
+- Only use relative imports within the `math` directory / module, e.g. `use self::fabs::fabs` or
+`use super::k_cos`. Absolute imports from core are OK, e.g. `use core::u64`.
+
+- To reinterpret a float as an integer use the `to_bits` method. The MUSL code uses the
+  `GET_FLOAT_WORD` macro, or a union, to do this operation.
+
+- To reinterpret an integer as a float use the `f32::from_bits` constructor. The MUSL code uses the
+  `SET_FLOAT_WORD` macro, or a union, to do this operation.
+
+- You may use other methods from core like `f64::is_nan`, etc. as appropriate.
+
+- If you're implementing one of the private double-underscore functions, take a look at the
+  "source" name in the comment at the top for an idea for alternate naming. For example, `__sin`
+  was renamed to `k_sin` after the FreeBSD source code naming. Do `use` these private functions in
+  `mod.rs`.
+
+- You may encounter weird literals like `0x1p127f` in the MUSL code. These are hexadecimal floating
+  point literals. Rust (the language) doesn't support these kind of literals. The best way I have
+  found to deal with these literals is to turn them into their integer representation using the
+  [`hexf!`] macro and then turn them back into floats. See below:
+
+[`hexf!`]: https://crates.io/crates/hexf
+
+``` rust
+// Step 1: write a program to convert the float into its integer representation
+#[macro_use]
+extern crate hexf;
+
+fn main() {
+    println!("{:#x}", hexf32!("0x1.0p127").to_bits());
+}
+```
+
+``` console
+$ # Step 2: run the program
+$ cargo run
+0x7f000000
+```
+
+``` rust
+// Step 3: copy paste the output into libm
+let x1p127 = f32::from_bits(0x7f000000); // 0x1p127f === 2 ^ 12
+```
+
+- Rust code panics on arithmetic overflows when not optimized. You may need to use the [`Wrapping`]
+  newtype to avoid this problem.
+
+[`Wrapping`]: https://doc.rust-lang.org/std/num/struct.Wrapping.html
+
+## Testing
+
+Normal tests can be executed with:
+
+```
+cargo test
+```
+
+If you'd like to run tests with randomized inputs that get compared against musl
+itself, you'll need to be on a Linux system and then you can execute:
+
+```
+cargo test --features musl-reference-tests
+```
+
+Note that you may need to pass `--release` to Cargo if there are errors related
+to integer overflow.