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//! Shared utilities for lexical conversion routines.
//!
//! These are not meant to be used publicly for any numeric
//! conversion routines, but provide optimized math routines,
//! format packed struct definitions, and custom iterators
//! for all workspaces.
//!
//! # Features
//!
//! * `std` - Use the standard library.
//! * `power-of-two` - Add support for parsing power-of-two integer strings.
//! * `radix` - Add support for strings of any radix.
//! * `write-integers` - Add support for writing integers.
//! * `write-floats` - Add support for writing floats.
//! * `parse-integers` - Add support for parsing integers.
//! * `parse-floats` - Add support for parsing floats.
//! * `compact` - Reduce code size at the cost of performance.
//!
//! # Note
//!
//! None of this is considered a public API: any of the implementation
//! details may change release-to-release without major or minor version
//! changes. Use internal implementation details at your own risk.
//!
//! lexical-util mainly exists as an implementation detail for
//! lexical-core, although its API is stable. If you would like to use
//! a high-level API that writes to and parses from `String` and `&str`,
//! respectively, please look at [lexical](https://crates.io/crates/lexical)
//! instead. If you would like an API that supports multiple numeric
//! conversions, please look at [lexical-core](https://crates.io/crates/lexical-core)
//! instead.
//!
//! # Version Support
//!
//! The minimum, standard, required version is 1.63.0, for const generic
//! support. Older versions of lexical support older Rust versions.
//!
//! # Safety Guarantees
//!
//! The only major sources of unsafe code are wrapped in the `iterator.rs`,
//! `skip.rs`, and `noskip.rs`. These are fully encapsulated into standalone
//! traits to clearly define safety invariants and localize any unsafety to
//! 1 or 2 lines of code.
//!
//! The core, unsafe trait is `BytesIter` and `Buffer`, both which expect
//! to be backed by a contiguous block of memory (a slice) but may skip
//! bytes internally. To guarantee safety, for non-skip iterators you
//! must implement [BytesIter::is_consumed][is_consumed] correctly.
//!
//! This must correctly determine if there are any elements left in the
//! iterator. If the buffer is contiguous, this can just be `index ==
//! self.len()`, but for a non-contiguous iterator it must skip any digits to
//! advance to the element next to be returned or the iterator itself will be
//! unsafe. **ALL** other safety invariants depend on this being implemented
//! correctly.
//!
//! To see if the cursor is at the end of the buffer, use
//! [BytesIter::is_done][is_done].
//!
//! Any iterators must be peekable: you must be able to read and return the next
//! value without advancing the iterator past that point. For iterators that
//! skip bytes, this means advancing to the next element to be returned and
//! returning that value. Therefore, [peek_unchecked] for skip iterators must be
//! implemented in terms of [peek]: you must peek the next element and
//! [peek_unchecked] will merely unwrap this value. Contiguous iterators can use
//! raw indexing instead.
//!
//! For examples of how to safely implement skip iterators, you can do something
//! like:
//!
//! ```rust,ignore
//! unsafe impl<_> BytesIter<_> for MyIter {
//! fn peek(&mut self) -> Option<u8> {
//! loop {
//! let value = self.bytes.get(self.index)?;
//! if value != &b'.' {
//! return value;
//! }
//! self.index += 1;
//! }
//! }
//! }
//! ```
//!
//! Then, [next](core::iter::Iterator::next) will be implemented in terms
//! of [peek], incrementing the position in the cursor just after the value.
//! The next iteration of peek will step to the correct byte to return.
//!
//! ```rust,ignore
//! impl<_> Iterator for MyIter {
//! type Item = &'a u8;
//!
//! fn next(&mut self) -> Option<Self::Item> {
//! let value = self.peek()?;
//! self.index += 1;
//! Some(value)
//! }
//! }
//! ```
//!
//! [is_done]: iterator::BytesIter::is_done
//! [is_consumed]: iterator::BytesIter::is_consumed
//! [peek]: iterator::BytesIter::peek
//! [peek_unchecked]: iterator::BytesIter::peek_unchecked
// We want to have the same safety guarantees as Rust core,
// so we allow unused unsafe to clearly document safety guarantees.