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//! SIMD-accelerated base64 encoding and decoding.
//!
//! # Examples
//!
//! ```
//! use base64_simd::Base64;
//!
//! let bytes = b"hello world";
//! let base64 = Base64::STANDARD;
//!
//! let encoded = base64.encode_to_boxed_str(bytes);
//! assert_eq!(&*encoded, "aGVsbG8gd29ybGQ=");
//!
//! let decoded = base64.decode_to_boxed_bytes(encoded.as_bytes()).unwrap();
//! assert_eq!(&*decoded, bytes);
//! ```
//!

#![cfg_attr(not(any(feature = "std", test)), no_std)]
#![cfg_attr(feature = "unstable", feature(arm_target_feature))]
//
#![deny(
    missing_debug_implementations,
    missing_docs,
    clippy::all,
    clippy::cargo,
    clippy::missing_inline_in_public_items
)]
#![warn(clippy::todo)]

#[cfg(feature = "alloc")]
extern crate alloc;

pub use simd_abstraction::tools::OutBuf;

mod error;
pub use self::error::Error;
pub(crate) use self::error::ERROR;

mod utils;

#[cfg(test)]
mod tests;

pub mod fallback;

#[macro_use]
mod generic;

mod polyfill;

pub mod arch;

mod auto;

mod ext;

#[derive(Debug)]
enum Base64Kind {
    Standard,
    UrlSafe,
}

/// Base64 variants
///
/// + [`Base64::STANDARD`](crate::Base64::STANDARD)
/// + [`Base64::STANDARD_NO_PAD`](crate::Base64::STANDARD_NO_PAD)
/// + [`Base64::URL_SAFE`](crate::Base64::URL_SAFE)
/// + [`Base64::URL_SAFE_NO_PAD`](crate::Base64::URL_SAFE_NO_PAD)
///
#[derive(Debug)]
pub struct Base64 {
    kind: Base64Kind,
    padding: bool,
}

impl Base64 {
    const PAD: u8 = b'=';

    /// Standard charset with padding.
    pub const STANDARD: Self = Self {
        kind: Base64Kind::Standard,
        padding: true,
    };

    /// Standard charset without padding.
    pub const STANDARD_NO_PAD: Self = Self {
        kind: Base64Kind::Standard,
        padding: false,
    };

    /// URL-safe charset with padding.
    pub const URL_SAFE: Self = Self {
        kind: Base64Kind::UrlSafe,
        padding: true,
    };

    /// URL-safe charset without padding.
    pub const URL_SAFE_NO_PAD: Self = Self {
        kind: Base64Kind::UrlSafe,
        padding: false,
    };

    #[inline(always)]
    const unsafe fn encoded_length_unchecked(n: usize, padding: bool) -> usize {
        let extra = n % 3;
        if extra == 0 {
            n / 3 * 4
        } else if padding {
            n / 3 * 4 + 4
        } else {
            n / 3 * 4 + extra + 1
        }
    }

    /// # Safety
    /// This function requires:
    ///
    /// + `src.len() > 0`
    #[inline(always)]
    unsafe fn decoded_length_unchecked(src: &[u8], padding: bool) -> Result<(usize, usize), Error> {
        let n = {
            let len = src.len();
            if padding {
                if len % 4 != 0 {
                    return Err(ERROR);
                }
                let last1 = *src.get_unchecked(len - 1);
                let last2 = *src.get_unchecked(len - 2);
                let count = (last1 == Base64::PAD) as usize + (last2 == Base64::PAD) as usize;
                len - count
            } else {
                len
            }
        };

        let m = match n % 4 {
            0 => n / 4 * 3,
            1 => return Err(ERROR),
            2 => n / 4 * 3 + 1,
            3 => n / 4 * 3 + 2,
            _ => core::hint::unreachable_unchecked(),
        };

        Ok((n, m))
    }

    /// Calcuates the encoding length.
    ///
    /// # Panics
    /// This function panics if any of the conditions below is not satisfied:
    ///
    /// + `n <= isize::MAX`
    #[inline]
    pub const fn encoded_length(&self, n: usize) -> usize {
        assert!(n <= (isize::MAX as usize));
        unsafe { Self::encoded_length_unchecked(n, self.padding) }
    }

    /// Returns the character set used for encoding.
    #[inline]
    pub const fn charset(&self) -> &[u8; 64] {
        match self.kind {
            Base64Kind::Standard => fallback::STANDARD_CHARSET,
            Base64Kind::UrlSafe => fallback::URL_SAFE_CHARSET,
        }
    }
}