#![no_std]

#![cfg_attr(docsrs, feature(doc_auto_cfg))]

#![doc(

    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",

    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"

)]

#![warn(

    clippy::mod_module_files,

    clippy::unwrap_used,

    missing_docs,

    rust_2018_idioms,

    unused_lifetimes,

    unused_qualifications

)]

//! Pure Rust implementation of Base16 ([RFC 4648], a.k.a. hex).

//!

//! Implements lower and upper case Base16 variants without data-dependent branches

//! or lookup  tables, thereby providing portable "best effort" constant-time

//! operation. Not constant-time with respect to message length (only data).

//!

//! Supports `no_std` environments and avoids heap allocations in the core API

//! (but also provides optional `alloc` support for convenience).

//!

//! Based on code from: <https://github.com/Sc00bz/ConstTimeEncoding/blob/master/hex.cpp>

//!

//! # Examples

//! ```

//! let lower_hex_str = "abcd1234";

//! let upper_hex_str = "ABCD1234";

//! let mixed_hex_str = "abCD1234";

//! let raw = b"\xab\xcd\x12\x34";

//!

//! let mut buf = [0u8; 16];

//! // length of return slice can be different from the input buffer!

//! let res = base16ct::lower::decode(lower_hex_str, &mut buf).unwrap();

//! assert_eq!(res, raw);

//! let res = base16ct::lower::encode(raw, &mut buf).unwrap();

//! assert_eq!(res, lower_hex_str.as_bytes());

//! // you also can use `encode_str` and `encode_string` to get

//! // `&str` and `String` respectively

//! let res: &str = base16ct::lower::encode_str(raw, &mut buf).unwrap();

//! assert_eq!(res, lower_hex_str);

//!

//! let res = base16ct::upper::decode(upper_hex_str, &mut buf).unwrap();

//! assert_eq!(res, raw);

//! let res = base16ct::upper::encode(raw, &mut buf).unwrap();

//! assert_eq!(res, upper_hex_str.as_bytes());

//!

//! // In cases when you don't know if input contains upper or lower

//! // hex-encoded value, then use functions from the `mixed` module

//! let res = base16ct::mixed::decode(lower_hex_str, &mut buf).unwrap();

//! assert_eq!(res, raw);

//! let res = base16ct::mixed::decode(upper_hex_str, &mut buf).unwrap();

//! assert_eq!(res, raw);

//! let res = base16ct::mixed::decode(mixed_hex_str, &mut buf).unwrap();

//! assert_eq!(res, raw);

//! ```

//!

//! [RFC 4648]: https://tools.ietf.org/html/rfc4648

#[cfg(feature = "alloc")]

#[macro_use]

extern crate alloc;

#[cfg(feature = "std")]

extern crate std;

/// Function for decoding and encoding lower Base16 (hex)

pub mod lower;

/// Function for decoding mixed Base16 (hex)

pub mod mixed;

/// Function for decoding and encoding upper Base16 (hex)

pub mod upper;

/// Display formatter for hex.

mod display;

/// Error types.

mod error;

pub use crate::{

    display::HexDisplay,

    error::{Error, Result},

};

#[cfg(feature = "alloc")]

use alloc::{string::String, vec::Vec};

/// Compute decoded length of the given hex-encoded input.

#[inline(always)]

pub fn decoded_len(bytes: &[u8]) -> Result<usize> {

    if bytes.len() & 1 == 0 {

        Ok(bytes.len() / 2)

    } else {

        Err(Error::InvalidLength)

    }

}

/// Get the length of Base16 (hex) produced by encoding the given bytes.

#[inline(always)]

pub fn encoded_len(bytes: &[u8]) -> usize {

    bytes.len() * 2

}

fn decode_inner<'a>(

    src: &[u8],

    dst: &'a mut [u8],

    decode_nibble: impl Fn(u8) -> u16,

) -> Result<&'a [u8]> {

    let dst = dst

        .get_mut(..decoded_len(src)?)

        .ok_or(Error::InvalidLength)?;

    let mut err: u16 = 0;

    for (src, dst) in src.chunks_exact(2).zip(dst.iter_mut()) {

        let byte = (decode_nibble(src[0]) << 4) | decode_nibble(src[1]);

        err |= byte >> 8;

        *dst = byte as u8;

    }

    match err {

        0 => Ok(dst),

        _ => Err(Error::InvalidEncoding),

    }

}