tasm_lib/arithmetic/u32/
safe_sub.rs

1use std::collections::HashMap;
2
3use triton_vm::prelude::*;
4
5use crate::prelude::*;
6use crate::traits::basic_snippet::Reviewer;
7use crate::traits::basic_snippet::SignOffFingerprint;
8
9/// Subtract two `u32`s and crash on overflow.
10///
11/// ### Behavior
12///
13/// ```text
14/// BEFORE: _ [right: 32] [left: u32]
15/// AFTER:  _ [left - right: u32]
16/// ```
17///
18/// ### Preconditions
19///
20/// - all input arguments are properly [`BFieldCodec`] encoded
21/// - `left` is greater than or equal to `right`
22///
23/// ### Postconditions
24///
25/// - the output is properly [`BFieldCodec`] encoded
26#[derive(Debug, Default, Copy, Clone, Eq, PartialEq, Hash)]
27pub struct SafeSub;
28
29impl SafeSub {
30    pub const OVERFLOW_ERROR_ID: i128 = 470;
31}
32
33impl BasicSnippet for SafeSub {
34    fn inputs(&self) -> Vec<(DataType, String)> {
35        ["right", "left"]
36            .map(|s| (DataType::U32, s.to_string()))
37            .to_vec()
38    }
39
40    fn outputs(&self) -> Vec<(DataType, String)> {
41        vec![(DataType::U32, "left - right".to_string())]
42    }
43
44    fn entrypoint(&self) -> String {
45        "tasmlib_arithmetic_u32_safe_sub".to_string()
46    }
47
48    fn code(&self, _: &mut Library) -> Vec<LabelledInstruction> {
49        triton_asm!(
50            // BEFORE: _ right left
51            // AFTER:  _ (left - right)
52            {self.entrypoint()}:
53                pick 1
54                push -1
55                mul
56                add
57                dup 0   // _ diff diff
58                split   // _ diff hi lo
59                pop 1   // _ diff hi
60                push 0  // _ diff hi 0
61                eq      // _ diff (hi == 0)
62                assert error_id {Self::OVERFLOW_ERROR_ID}
63                return
64        )
65    }
66
67    fn sign_offs(&self) -> HashMap<Reviewer, SignOffFingerprint> {
68        let mut sign_offs = HashMap::new();
69        sign_offs.insert(Reviewer("ferdinand"), 0x40fd42d47d3b4bf4.into());
70        sign_offs
71    }
72}
73
74#[cfg(test)]
75mod tests {
76    use super::*;
77    use crate::test_prelude::*;
78
79    impl Closure for SafeSub {
80        type Args = (u32, u32);
81
82        fn rust_shadow(&self, stack: &mut Vec<BFieldElement>) {
83            let (right, left) = pop_encodable::<Self::Args>(stack);
84            let diff = left.checked_sub(right).unwrap();
85            push_encodable(stack, &diff);
86        }
87
88        fn pseudorandom_args(
89            &self,
90            seed: [u8; 32],
91            bench_case: Option<BenchmarkCase>,
92        ) -> Self::Args {
93            let Some(bench_case) = bench_case else {
94                let mut rng = StdRng::from_seed(seed);
95                let left = rng.random();
96                let right = rng.random_range(0..=left);
97
98                return (right, left);
99            };
100
101            match bench_case {
102                BenchmarkCase::CommonCase => (1 << 15, 1 << 16),
103                BenchmarkCase::WorstCase => (0, u32::MAX),
104            }
105        }
106
107        fn corner_case_args(&self) -> Vec<Self::Args> {
108            vec![(0, 0), (0, u32::MAX), (u32::MAX, u32::MAX)]
109        }
110    }
111
112    #[test]
113    fn rust_shadow() {
114        ShadowedClosure::new(SafeSub).test();
115    }
116
117    #[proptest]
118    fn overflow_crashes_vm(
119        #[filter(#left != u32::MAX)] left: u32,
120        #[strategy(#left..)] right: u32,
121    ) {
122        test_assertion_failure(
123            &ShadowedClosure::new(SafeSub),
124            InitVmState::with_stack(SafeSub.set_up_test_stack((right, left))),
125            &[SafeSub::OVERFLOW_ERROR_ID],
126        )
127    }
128}
129
130#[cfg(test)]
131mod benches {
132    use super::*;
133    use crate::test_prelude::*;
134
135    #[test]
136    fn safe_sub_benchmark() {
137        ShadowedClosure::new(SafeSub).bench();
138    }
139}
tasm_lib/arithmetic/u32/safe_sub.rs

tasm_lib/arithmetic/u32/
safe_sub.rs
