snarkvm_console_types_integers/
from_field.rs

1// Copyright (c) 2019-2025 Provable Inc.
2// This file is part of the snarkVM library.
3
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at:
7
8// http://www.apache.org/licenses/LICENSE-2.0
9
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15
16use super::*;
17
18impl<E: Environment, I: IntegerType> FromField for Integer<E, I> {
19    type Field = Field<E>;
20
21    /// Casts an integer from a base field.
22    ///
23    /// This method guarantees the following:
24    ///   1. If the field element is larger than the integer domain, then the operation will fail.
25    ///   2. If the field element is smaller than the integer domain, then the operation will succeed.
26    fn from_field(field: &Self::Field) -> Result<Self> {
27        // Note: We are reconstituting the integer from the base field.
28        // This is safe as the number of bits in the integer is less than the base field modulus,
29        // and thus will always fit within a single base field element.
30        debug_assert!(I::BITS < Field::<E>::size_in_bits() as u64);
31
32        // Convert the field element into bits.
33        let bits_le = field.to_bits_le();
34
35        // Extract the integer bits from the field element, **without** a carry bit.
36        let (bits_le, zero_bits) = bits_le.split_at(Self::size_in_bits());
37
38        // Ensure the unused upper bits are all zero.
39        ensure!(zero_bits.iter().all(|&bit| !bit), "Failed to convert field to integer: upper bits are not zero");
40
41        // Return the integer.
42        Self::from_bits_le(bits_le)
43    }
44}
45
46#[cfg(test)]
47mod tests {
48    use super::*;
49    use snarkvm_console_network_environment::Console;
50
51    type CurrentEnvironment = Console;
52
53    const ITERATIONS: u64 = 10_000;
54
55    fn check_from_field<I: IntegerType>() -> Result<()> {
56        let mut rng = TestRng::default();
57
58        for _ in 0..ITERATIONS {
59            // Sample a random integer.
60            let expected = Integer::<CurrentEnvironment, I>::rand(&mut rng);
61
62            // Perform the operation.
63            let candidate = Integer::from_field(&expected.to_field()?)?;
64            assert_eq!(expected, candidate);
65
66            // Sample a random field.
67            let expected = Field::<CurrentEnvironment>::rand(&mut rng);
68            // Determine the integer domain.
69            let integer_max = match I::type_name() {
70                "u8" | "i8" => Field::<CurrentEnvironment>::from_u8(u8::MAX),
71                "u16" | "i16" => Field::<CurrentEnvironment>::from_u16(u16::MAX),
72                "u32" | "i32" => Field::<CurrentEnvironment>::from_u32(u32::MAX),
73                "u64" | "i64" => Field::<CurrentEnvironment>::from_u64(u64::MAX),
74                "u128" | "i128" => Field::<CurrentEnvironment>::from_u128(u128::MAX),
75                _ => panic!("Unsupported integer type."),
76            };
77            // Filter for field elements that exceed the integer domain.
78            if expected > integer_max {
79                // Perform the operation.
80                assert!(Integer::<_, I>::from_field(&expected).is_err());
81            } else {
82                // Perform the operation.
83                assert!(Integer::<_, I>::from_field(&expected).is_ok());
84            }
85        }
86        Ok(())
87    }
88
89    #[test]
90    fn test_u8_from_field() -> Result<()> {
91        type I = u8;
92        check_from_field::<I>()
93    }
94
95    #[test]
96    fn test_i8_from_field() -> Result<()> {
97        type I = i8;
98        check_from_field::<I>()
99    }
100
101    #[test]
102    fn test_u16_from_field() -> Result<()> {
103        type I = u16;
104        check_from_field::<I>()
105    }
106
107    #[test]
108    fn test_i16_from_field() -> Result<()> {
109        type I = i16;
110        check_from_field::<I>()
111    }
112
113    #[test]
114    fn test_u32_from_field() -> Result<()> {
115        type I = u32;
116        check_from_field::<I>()
117    }
118
119    #[test]
120    fn test_i32_from_field() -> Result<()> {
121        type I = i32;
122        check_from_field::<I>()
123    }
124
125    #[test]
126    fn test_u64_from_field() -> Result<()> {
127        type I = u64;
128        check_from_field::<I>()
129    }
130
131    #[test]
132    fn test_i64_from_field() -> Result<()> {
133        type I = i64;
134        check_from_field::<I>()
135    }
136
137    #[test]
138    fn test_u128_from_field() -> Result<()> {
139        type I = u128;
140        check_from_field::<I>()
141    }
142
143    #[test]
144    fn test_i128_from_field() -> Result<()> {
145        type I = i128;
146        check_from_field::<I>()
147    }
148}
snarkvm_console_types_integers/from_field.rs

snarkvm_console_types_integers/
from_field.rs
