/rust/registry/src/index.crates.io-1949cf8c6b5b557f/base64ct-1.8.0/src/alphabet.rs

Source
//! Base64 alphabets.

// TODO(tarcieri): explicitly checked/wrapped arithmetic
#![allow(clippy::arithmetic_side_effects)]

use core::{fmt::Debug, ops::RangeInclusive};

pub mod bcrypt;
pub mod crypt;
pub mod shacrypt;
pub mod standard;
pub mod url;

/// Core encoder/decoder functions for a particular Base64 alphabet.
pub trait Alphabet: 'static + Copy + Debug + Eq + Send + Sized + Sync {
    /// First character in this Base64 alphabet.
    const BASE: u8;

    /// Decoder passes
    const DECODER: &'static [DecodeStep];

    /// Encoder passes
    const ENCODER: &'static [EncodeStep];

    /// Is this encoding padded?
    const PADDED: bool;

    /// Unpadded equivalent of this alphabet.
    ///
    /// For alphabets that are unpadded to begin with, this should be `Self`.
    type Unpadded: Alphabet;

    /// Decode 3 bytes of a Base64 message.
    #[inline(always)]
    fn decode_3bytes(src: &[u8], dst: &mut [u8]) -> i16 {
        debug_assert_eq!(src.len(), 4);
        debug_assert!(dst.len() >= 3, "dst too short: {}", dst.len());

        let c0 = Self::decode_6bits(src[0]);
        let c1 = Self::decode_6bits(src[1]);
        let c2 = Self::decode_6bits(src[2]);
        let c3 = Self::decode_6bits(src[3]);

        dst[0] = ((c0 << 2) | (c1 >> 4)) as u8;
        dst[1] = ((c1 << 4) | (c2 >> 2)) as u8;
        dst[2] = ((c2 << 6) | c3) as u8;

        ((c0 | c1 | c2 | c3) >> 8) & 1
    }

    /// Decode 6-bits of a Base64 message.
    fn decode_6bits(src: u8) -> i16 {
        let mut ret: i16 = -1;

        for step in Self::DECODER {
            ret += match step {
                DecodeStep::Range(range, offset) => {
                    // Compute exclusive range from inclusive one
                    let start = *range.start() as i16 - 1;
                    let end = *range.end() as i16 + 1;
                    (((start - src as i16) & (src as i16 - end)) >> 8) & (src as i16 + *offset)
                }
                DecodeStep::Eq(value, offset) => {
                    let start = *value as i16 - 1;
                    let end = *value as i16 + 1;
                    (((start - src as i16) & (src as i16 - end)) >> 8) & *offset
                }
            };
        }

        ret
    }

    /// Encode 3-bytes of a Base64 message.
    #[inline(always)]
    fn encode_3bytes(src: &[u8], dst: &mut [u8]) {
        debug_assert_eq!(src.len(), 3);
        debug_assert!(dst.len() >= 4, "dst too short: {}", dst.len());

        let b0 = src[0] as i16;
        let b1 = src[1] as i16;
        let b2 = src[2] as i16;

        dst[0] = Self::encode_6bits(b0 >> 2);
        dst[1] = Self::encode_6bits(((b0 << 4) | (b1 >> 4)) & 63);
        dst[2] = Self::encode_6bits(((b1 << 2) | (b2 >> 6)) & 63);
        dst[3] = Self::encode_6bits(b2 & 63);
    }

    /// Encode 6-bits of a Base64 message.
    #[inline(always)]
    fn encode_6bits(src: i16) -> u8 {
        let mut diff = src + Self::BASE as i16;

        for &step in Self::ENCODER {
            diff += match step {
                EncodeStep::Apply(threshold, offset) => ((threshold as i16 - diff) >> 8) & offset,
                EncodeStep::Diff(threshold, offset) => ((threshold as i16 - src) >> 8) & offset,
            };
        }

        diff as u8
    }
}

/// Constant-time decoder step.
#[derive(Debug)]
pub enum DecodeStep {
    /// Match the given range, offsetting the input on match.
    Range(RangeInclusive<u8>, i16),

    /// Match the given value, returning the associated offset on match.
    Eq(u8, i16),
}

/// Constant-time encoder step.
#[derive(Copy, Clone, Debug)]
pub enum EncodeStep {
    /// Apply the given offset to the cumulative result on match.
    Apply(u8, i16),

    /// Compute a difference using the given offset on match.
    Diff(u8, i16),
}

Line	Count	Source
1		//! Base64 alphabets.
2
3		// TODO(tarcieri): explicitly checked/wrapped arithmetic
4		#![allow(clippy::arithmetic_side_effects)]
5
6		use core::{fmt::Debug, ops::RangeInclusive};
7
8		pub mod bcrypt;
9		pub mod crypt;
10		pub mod shacrypt;
11		pub mod standard;
12		pub mod url;
13
14		/// Core encoder/decoder functions for a particular Base64 alphabet.
15		pub trait Alphabet: 'static + Copy + Debug + Eq + Send + Sized + Sync {
16		/// First character in this Base64 alphabet.
17		const BASE: u8;
18
19		/// Decoder passes
20		const DECODER: &'static [DecodeStep];
21
22		/// Encoder passes
23		const ENCODER: &'static [EncodeStep];
24
25		/// Is this encoding padded?
26		const PADDED: bool;
27
28		/// Unpadded equivalent of this alphabet.
29		///
30		/// For alphabets that are unpadded to begin with, this should be `Self`.
31		type Unpadded: Alphabet;
32
33		/// Decode 3 bytes of a Base64 message.
34		#[inline(always)]
35	0	fn decode_3bytes(src: &[u8], dst: &mut [u8]) -> i16 {
36	0	debug_assert_eq!(src.len(), 4);
37	0	debug_assert!(dst.len() >= 3, "dst too short: {}", dst.len());
38
39	0	let c0 = Self::decode_6bits(src[0]);
40	0	let c1 = Self::decode_6bits(src[1]);
41	0	let c2 = Self::decode_6bits(src[2]);
42	0	let c3 = Self::decode_6bits(src[3]);
43
44	0	dst[0] = ((c0 << 2) \| (c1 >> 4)) as u8;
45	0	dst[1] = ((c1 << 4) \| (c2 >> 2)) as u8;
46	0	dst[2] = ((c2 << 6) \| c3) as u8;
47
48	0	((c0 \| c1 \| c2 \| c3) >> 8) & 1
49	0	} Unexecuted instantiation: <base64ct::alphabet::crypt::Base64Crypt as base64ct::alphabet::Alphabet>::decode_3bytes Unexecuted instantiation: <base64ct::alphabet::bcrypt::Base64Bcrypt as base64ct::alphabet::Alphabet>::decode_3bytes Unexecuted instantiation: <base64ct::alphabet::standard::Base64Unpadded as base64ct::alphabet::Alphabet>::decode_3bytes Unexecuted instantiation: <_ as base64ct::alphabet::Alphabet>::decode_3bytes
50
51		/// Decode 6-bits of a Base64 message.
52	0	fn decode_6bits(src: u8) -> i16 {
53	0	let mut ret: i16 = -1;
54
55	0	for step in Self::DECODER {
56	0	ret += match step {
57	0	DecodeStep::Range(range, offset) => {
58		// Compute exclusive range from inclusive one
59	0	let start = *range.start() as i16 - 1;
60	0	let end = *range.end() as i16 + 1;
61	0	(((start - src as i16) & (src as i16 - end)) >> 8) & (src as i16 + *offset)
62		}
63	0	DecodeStep::Eq(value, offset) => {
64	0	let start = *value as i16 - 1;
65	0	let end = *value as i16 + 1;
66	0	(((start - src as i16) & (src as i16 - end)) >> 8) & *offset
67		}
68		};
69		}
70
71	0	ret
72	0	} Unexecuted instantiation: <base64ct::alphabet::crypt::Base64Crypt as base64ct::alphabet::Alphabet>::decode_6bits Unexecuted instantiation: <base64ct::alphabet::bcrypt::Base64Bcrypt as base64ct::alphabet::Alphabet>::decode_6bits Unexecuted instantiation: <base64ct::alphabet::standard::Base64Unpadded as base64ct::alphabet::Alphabet>::decode_6bits Unexecuted instantiation: <_ as base64ct::alphabet::Alphabet>::decode_6bits
73
74		/// Encode 3-bytes of a Base64 message.
75		#[inline(always)]
76	0	fn encode_3bytes(src: &[u8], dst: &mut [u8]) {
77	0	debug_assert_eq!(src.len(), 3);
78	0	debug_assert!(dst.len() >= 4, "dst too short: {}", dst.len());
79
80	0	let b0 = src[0] as i16;
81	0	let b1 = src[1] as i16;
82	0	let b2 = src[2] as i16;
83
84	0	dst[0] = Self::encode_6bits(b0 >> 2);
85	0	dst[1] = Self::encode_6bits(((b0 << 4) \| (b1 >> 4)) & 63);
86	0	dst[2] = Self::encode_6bits(((b1 << 2) \| (b2 >> 6)) & 63);
87	0	dst[3] = Self::encode_6bits(b2 & 63);
88	0	} Unexecuted instantiation: <base64ct::alphabet::crypt::Base64Crypt as base64ct::alphabet::Alphabet>::encode_3bytes Unexecuted instantiation: <base64ct::alphabet::bcrypt::Base64Bcrypt as base64ct::alphabet::Alphabet>::encode_3bytes Unexecuted instantiation: <base64ct::alphabet::standard::Base64Unpadded as base64ct::alphabet::Alphabet>::encode_3bytes Unexecuted instantiation: <_ as base64ct::alphabet::Alphabet>::encode_3bytes
89
90		/// Encode 6-bits of a Base64 message.
91		#[inline(always)]
92	0	fn encode_6bits(src: i16) -> u8 {
93	0	let mut diff = src + Self::BASE as i16;
94
95	0	for &step in Self::ENCODER {
96	0	diff += match step {
97	0	EncodeStep::Apply(threshold, offset) => ((threshold as i16 - diff) >> 8) & offset,
98	0	EncodeStep::Diff(threshold, offset) => ((threshold as i16 - src) >> 8) & offset,
99		};
100		}
101
102	0	diff as u8
103	0	} Unexecuted instantiation: <base64ct::alphabet::crypt::Base64Crypt as base64ct::alphabet::Alphabet>::encode_6bits Unexecuted instantiation: <base64ct::alphabet::bcrypt::Base64Bcrypt as base64ct::alphabet::Alphabet>::encode_6bits Unexecuted instantiation: <base64ct::alphabet::standard::Base64Unpadded as base64ct::alphabet::Alphabet>::encode_6bits Unexecuted instantiation: <_ as base64ct::alphabet::Alphabet>::encode_6bits
104		}
105
106		/// Constant-time decoder step.
107		#[derive(Debug)]
108		pub enum DecodeStep {
109		/// Match the given range, offsetting the input on match.
110		Range(RangeInclusive<u8>, i16),
111
112		/// Match the given value, returning the associated offset on match.
113		Eq(u8, i16),
114		}
115
116		/// Constant-time encoder step.
117		#[derive(Copy, Clone, Debug)]
118		pub enum EncodeStep {
119		/// Apply the given offset to the cumulative result on match.
120		Apply(u8, i16),
121
122		/// Compute a difference using the given offset on match.
123		Diff(u8, i16),
124		}

Coverage Report

Created: 2025-11-11 06:12