num_bigint/biguint/
serde.rs

1#![cfg(feature = "serde")]
2#![cfg_attr(docsrs, doc(cfg(feature = "serde")))]
3
4use super::{biguint_from_vec, BigUint};
5
6use alloc::vec::Vec;
7use core::{cmp, fmt, mem};
8use serde::de::{SeqAccess, Visitor};
9use serde::{Deserialize, Deserializer, Serialize, Serializer};
10
11// `cautious` is based on the function of the same name in `serde`, but specialized to `u32`:
12// https://github.com/dtolnay/serde/blob/399ef081ecc36d2f165ff1f6debdcbf6a1dc7efb/serde/src/private/size_hint.rs#L11-L22
13fn cautious(hint: Option<usize>) -> usize {
14    const MAX_PREALLOC_BYTES: usize = 1024 * 1024;
15
16    cmp::min(
17        hint.unwrap_or(0),
18        MAX_PREALLOC_BYTES / mem::size_of::<u32>(),
19    )
20}
21
22impl Serialize for BigUint {
23    cfg_digit!(
24        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
25        where
26            S: Serializer,
27        {
28            // Note: do not change the serialization format, or it may break forward
29            // and backward compatibility of serialized data!  If we ever change the
30            // internal representation, we should still serialize in base-`u32`.
31            let data: &[u32] = &self.data;
32            data.serialize(serializer)
33        }
34
35        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
36        where
37            S: Serializer,
38        {
39            use serde::ser::SerializeSeq;
40
41            if let Some((&last, data)) = self.data.split_last() {
42                let last_lo = last as u32;
43                let last_hi = (last >> 32) as u32;
44                let u32_len = data.len() * 2 + 1 + (last_hi != 0) as usize;
45                let mut seq = serializer.serialize_seq(Some(u32_len))?;
46                for &x in data {
47                    seq.serialize_element(&(x as u32))?;
48                    seq.serialize_element(&((x >> 32) as u32))?;
49                }
50                seq.serialize_element(&last_lo)?;
51                if last_hi != 0 {
52                    seq.serialize_element(&last_hi)?;
53                }
54                seq.end()
55            } else {
56                let data: &[u32] = &[];
57                data.serialize(serializer)
58            }
59        }
60    );
61}
62
63impl<'de> Deserialize<'de> for BigUint {
64    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
65    where
66        D: Deserializer<'de>,
67    {
68        deserializer.deserialize_seq(U32Visitor)
69    }
70}
71
72struct U32Visitor;
73
74impl<'de> Visitor<'de> for U32Visitor {
75    type Value = BigUint;
76
77    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
78        formatter.write_str("a sequence of unsigned 32-bit numbers")
79    }
80
81    cfg_digit!(
82        fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
83        where
84            S: SeqAccess<'de>,
85        {
86            let len = cautious(seq.size_hint());
87            let mut data = Vec::with_capacity(len);
88
89            while let Some(value) = seq.next_element::<u32>()? {
90                data.push(value);
91            }
92
93            Ok(biguint_from_vec(data))
94        }
95
96        fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
97        where
98            S: SeqAccess<'de>,
99        {
100            use crate::big_digit::BigDigit;
101            use num_integer::Integer;
102
103            let u32_len = cautious(seq.size_hint());
104            let len = Integer::div_ceil(&u32_len, &2);
105            let mut data = Vec::with_capacity(len);
106
107            while let Some(lo) = seq.next_element::<u32>()? {
108                let mut value = BigDigit::from(lo);
109                if let Some(hi) = seq.next_element::<u32>()? {
110                    value |= BigDigit::from(hi) << 32;
111                    data.push(value);
112                } else {
113                    data.push(value);
114                    break;
115                }
116            }
117
118            Ok(biguint_from_vec(data))
119        }
120    );
121}
num_bigint/biguint/serde.rs

num_bigint/biguint/
serde.rs
