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

use crate::backend::riscv::simple_instruction::{param::Decided, Param};
use nom::{bytes::complete::tag, combinator::map, IResult};

use super::IsParamTransformer;
use bitvec::prelude::*;

/// A transformer that extract the lower bits of an imm used for a branch instruction.
#[derive(Debug, Eq, PartialEq, Clone, Copy)]
pub struct BranchLow;

impl Default for BranchLow {
    fn default() -> Self {
        Self::new()
    }
}

impl BranchLow {
    pub const fn new() -> Self {
        Self
    }
}

pub fn parse(code: &str) -> IResult<&str, BranchLow> {
    map(tag("branch_low"), |_| BranchLow::new())(code)
}

impl IsParamTransformer for BranchLow {
    fn param_to_instruction_part(&self, offset: u64, param: &Param) -> BitVec<u32> {
        let param_bits_store = (param.unwrap_immediate() as i64 - offset as i64) as u32;
        let param_bits = param_bits_store.view_bits::<Lsb0>();
        let mut instruction_part = BitVec::new();
        instruction_part.push(param_bits[11]);
        instruction_part.extend_from_bitslice(&param_bits[1..5]);
        instruction_part
    }

    fn update_param(&self, instruction_part: &BitSlice<u32>, param: &mut Param) {
        if let Param::Decided(Decided::Immediate(param_value))
        | Param::Resolved(_, Decided::Immediate(param_value)) = param
        {
            let mut param_bits_store = *param_value as u32;
            let param_bits = param_bits_store.view_bits_mut::<Lsb0>();
            param_bits.set(11, instruction_part[0]);
            param_bits[1..5].copy_from_bitslice(&instruction_part[1..5]);
            *param_value = param_bits_store as i32;
        }
    }

    fn default_param(&self) -> Param {
        Param::Decided(Decided::Immediate(0))
    }
    fn bit_count(&self) -> usize {
        5
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::backend::riscv::simple_instruction::Param;

    #[test]
    fn test_argument_to_bits() {
        let transformer = BranchLow::new();
        let bits =
            transformer.param_to_instruction_part(0, &Param::Decided(Decided::Immediate(-4)));
        assert_eq!(bits, bits![u32, Lsb0; 1, 0, 1, 1, 1]);
        let bits = transformer.param_to_instruction_part(0, &Param::Decided(Decided::Immediate(4)));
        assert_eq!(bits, bits![u32, Lsb0; 0, 0, 1, 0, 0]);
        let bits =
            transformer.param_to_instruction_part(0, &Param::Decided(Decided::Immediate(0x998)));
        assert_eq!(bits, bits![u32, Lsb0; 1, 0, 0, 1, 1]);
    }

    #[test]
    fn test_update_argument() {
        let transformer = BranchLow::new();
        let mut param = Param::Decided(Decided::Immediate(0));
        transformer.update_param(bits![u32, Lsb0; 1, 0, 1, 1, 1], &mut param);
        assert_eq!(param, Param::Decided(Decided::Immediate(0b1000_0001_1100)));
    }
}