1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149

use crate::{
    evm_circuit::{
        execution::ExecutionGadget,
        step::ExecutionState,
        util::{
            common_gadget::SameContextGadget,
            constraint_builder::{EVMConstraintBuilder, StepStateTransition, Transition::Delta},
            CachedRegion,
        },
        witness::{Block, Call, Chunk, ExecStep, Transaction},
    },
    util::{
        word::{WordExpr, WordLoHiCell},
        Expr,
    },
};
use eth_types::{evm_types::OpcodeId, Field};
use halo2_proofs::plonk::Error;

#[derive(Clone, Debug)]
pub(crate) struct SwapGadget<F> {
    same_context: SameContextGadget<F>,
    values: [WordLoHiCell<F>; 2],
}

impl<F: Field> ExecutionGadget<F> for SwapGadget<F> {
    const NAME: &'static str = "SWAP";

    const EXECUTION_STATE: ExecutionState = ExecutionState::SWAP;

    fn configure(cb: &mut EVMConstraintBuilder<F>) -> Self {
        let opcode = cb.query_cell();

        let values = [cb.query_word_unchecked(), cb.query_word_unchecked()];

        // The stack index we have to peek, deduced from the 'x' value of
        // 'swapx' The offset starts at 1 for SWAP1
        let swap_offset = opcode.expr() - (OpcodeId::SWAP1.as_u64() - 1).expr();

        // Peek the value at `swap_offset`
        cb.stack_lookup(false.expr(), swap_offset.clone(), values[0].to_word());
        // Peek the value at the top of the stack
        cb.stack_lookup(false.expr(), 0.expr(), values[1].to_word());
        // Write the value previously at the top of the stack to `swap_offset`
        cb.stack_lookup(true.expr(), swap_offset, values[1].to_word());
        // Write the value previously at `swap_offset` to the top of the stack
        cb.stack_lookup(true.expr(), 0.expr(), values[0].to_word());

        // State transition
        let step_state_transition = StepStateTransition {
            rw_counter: Delta(4.expr()),
            program_counter: Delta(1.expr()),
            gas_left: Delta(-OpcodeId::SWAP1.constant_gas_cost().expr()),
            ..Default::default()
        };
        let same_context = SameContextGadget::construct(cb, opcode, step_state_transition);

        Self {
            same_context,
            values,
        }
    }

    fn assign_exec_step(
        &self,
        region: &mut CachedRegion<'_, '_, F>,
        offset: usize,
        block: &Block<F>,
        _chunk: &Chunk<F>,
        _: &Transaction,
        _: &Call,
        step: &ExecStep,
    ) -> Result<(), Error> {
        self.same_context.assign_exec_step(region, offset, step)?;

        for (cell, value) in self.values.iter().zip(
            [0, 1]
                .map(|index| block.get_rws(step, index).stack_value())
                .iter(),
        ) {
            cell.assign_u256(region, offset, *value)?;
        }

        Ok(())
    }
}

#[cfg(test)]
mod test {
    use crate::{evm_circuit::test::rand_word, test_util::CircuitTestBuilder};
    use eth_types::{bytecode, evm_types::OpcodeId, Word};
    use mock::TestContext;

    fn test_ok(opcode: OpcodeId, lhs: Word, rhs: Word) {
        let n = opcode.postfix().expect("opcode with postfix");

        let mut bytecode = bytecode! {
            PUSH32(lhs)
        };
        for _ in 0..n - 1 {
            bytecode.op_dup1();
        }
        bytecode.append(&bytecode! {
            PUSH32(rhs)
            .write_op(opcode)
            STOP
        });

        CircuitTestBuilder::new_from_test_ctx(
            TestContext::<2, 1>::simple_ctx_with_bytecode(bytecode).unwrap(),
        )
        .run();
    }

    #[test]
    fn swap_gadget_simple() {
        test_ok(OpcodeId::SWAP1, Word::from(0x030201), Word::from(0x040506));
        test_ok(OpcodeId::SWAP2, Word::from(0x030201), Word::from(0x040506));
        test_ok(OpcodeId::SWAP15, Word::from(0x030201), Word::from(0x040506));
        test_ok(OpcodeId::SWAP16, Word::from(0x030201), Word::from(0x040506));
    }

    #[test]
    #[ignore]
    fn swap_gadget_rand() {
        for opcode in vec![
            OpcodeId::SWAP1,
            OpcodeId::SWAP2,
            OpcodeId::SWAP3,
            OpcodeId::SWAP4,
            OpcodeId::SWAP5,
            OpcodeId::SWAP6,
            OpcodeId::SWAP7,
            OpcodeId::SWAP8,
            OpcodeId::SWAP9,
            OpcodeId::SWAP10,
            OpcodeId::SWAP11,
            OpcodeId::SWAP12,
            OpcodeId::SWAP13,
            OpcodeId::SWAP14,
            OpcodeId::SWAP15,
            OpcodeId::SWAP16,
        ]
        .into_iter()
        {
            test_ok(opcode, rand_word(), rand_word());
        }
    }
}