crypto_bigint/
limb.rs

1//! Big integers are represented as an array of smaller CPU word-size integers
2//! called "limbs".
3
4mod add;
5mod bit_and;
6mod bit_not;
7mod bit_or;
8mod bit_xor;
9mod bits;
10mod cmp;
11mod encoding;
12mod from;
13mod mul;
14mod neg;
15mod shl;
16mod shr;
17mod sub;
18
19#[cfg(feature = "rand_core")]
20mod rand;
21
22use crate::{Bounded, Zero};
23use core::fmt;
24use subtle::{Choice, ConditionallySelectable};
25
26#[cfg(feature = "serde")]
27use serdect::serde::{Deserialize, Deserializer, Serialize, Serializer};
28
29#[cfg(not(any(target_pointer_width = "32", target_pointer_width = "64")))]
30compile_error!("this crate builds on 32-bit and 64-bit platforms only");
31
32//
33// 32-bit definitions
34//
35
36/// Inner integer type that the [`Limb`] newtype wraps.
37#[cfg(target_pointer_width = "32")]
38pub type Word = u32;
39
40/// Unsigned wide integer type: double the width of [`Word`].
41#[cfg(target_pointer_width = "32")]
42pub type WideWord = u64;
43
44//
45// 64-bit definitions
46//
47
48/// Unsigned integer type that the [`Limb`] newtype wraps.
49#[cfg(target_pointer_width = "64")]
50pub type Word = u64;
51
52/// Wide integer type: double the width of [`Word`].
53#[cfg(target_pointer_width = "64")]
54pub type WideWord = u128;
55
56/// Highest bit in a [`Limb`].
57pub(crate) const HI_BIT: usize = Limb::BITS - 1;
58
59/// Big integers are represented as an array of smaller CPU word-size integers
60/// called "limbs".
61// Our PartialEq impl only differs from the default one by being constant-time, so this is safe
62#[allow(clippy::derived_hash_with_manual_eq)]
63#[derive(Copy, Clone, Default, Hash)]
64#[repr(transparent)]
65pub struct Limb(pub Word);
66
67impl Limb {
68    /// The value `0`.
69    pub const ZERO: Self = Limb(0);
70
71    /// The value `1`.
72    pub const ONE: Self = Limb(1);
73
74    /// Maximum value this [`Limb`] can express.
75    pub const MAX: Self = Limb(Word::MAX);
76
77    // 32-bit
78
79    /// Size of the inner integer in bits.
80    #[cfg(target_pointer_width = "32")]
81    pub const BITS: usize = 32;
82    /// Size of the inner integer in bytes.
83    #[cfg(target_pointer_width = "32")]
84    pub const BYTES: usize = 4;
85
86    // 64-bit
87
88    /// Size of the inner integer in bits.
89    #[cfg(target_pointer_width = "64")]
90    pub const BITS: usize = 64;
91    /// Size of the inner integer in bytes.
92    #[cfg(target_pointer_width = "64")]
93    pub const BYTES: usize = 8;
94}
95
96impl Bounded for Limb {
97    const BITS: usize = Self::BITS;
98    const BYTES: usize = Self::BYTES;
99}
100
101impl ConditionallySelectable for Limb {
102    #[inline]
103    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
104        Self(Word::conditional_select(&a.0, &b.0, choice))
105    }
106}
107
108impl Zero for Limb {
109    const ZERO: Self = Self::ZERO;
110}
111
112impl fmt::Debug for Limb {
113    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
114        write!(f, "Limb(0x{self:X})")
115    }
116}
117
118impl fmt::Display for Limb {
119    #[inline]
120    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
121        fmt::UpperHex::fmt(self, f)
122    }
123}
124
125impl fmt::LowerHex for Limb {
126    #[inline]
127    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
128        write!(f, "{:0width$x}", &self.0, width = Self::BYTES * 2)
129    }
130}
131
132impl fmt::UpperHex for Limb {
133    #[inline]
134    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
135        write!(f, "{:0width$X}", &self.0, width = Self::BYTES * 2)
136    }
137}
138
139#[cfg(feature = "serde")]
140impl<'de> Deserialize<'de> for Limb {
141    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
142    where
143        D: Deserializer<'de>,
144    {
145        Ok(Self(Word::deserialize(deserializer)?))
146    }
147}
148
149#[cfg(feature = "serde")]
150impl Serialize for Limb {
151    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
152    where
153        S: Serializer,
154    {
155        self.0.serialize(serializer)
156    }
157}
158
159#[cfg(feature = "zeroize")]
160impl zeroize::DefaultIsZeroes for Limb {}
161
162#[cfg(test)]
163mod tests {
164    #[cfg(feature = "alloc")]
165    use {super::Limb, alloc::format};
166
167    #[cfg(feature = "alloc")]
168    #[test]
169    fn debug() {
170        #[cfg(target_pointer_width = "32")]
171        assert_eq!(format!("{:?}", Limb(42)), "Limb(0x0000002A)");
172
173        #[cfg(target_pointer_width = "64")]
174        assert_eq!(format!("{:?}", Limb(42)), "Limb(0x000000000000002A)");
175    }
176}
crypto_bigint/limb.rs

crypto_bigint/
limb.rs
