Witch of Git - jade-rose/blob - toolchain/src/inst/decode.rs

   1 use super::{AddImm, AluI, Data, Inst, Op1, OpI3, OpR, Reg, Special, Target, U3};
   2 use std::io::{self, Read};
   3
   4 pub trait Decode: Sized {
   5     fn decode(reader: &mut impl Read) -> io::Result<Self>;
   6 }
   7
   8 fn reg(x: u8) -> Reg {
   9     Reg::new(x & 0x7).unwrap()
  10 }
  11
  12 fn special(x: u8) -> io::Result<Special> {
  13     match x {
  14         0b000 => Ok(Special::Data(Data::D1)),
  15         0b001 => Ok(Special::Data(Data::D2)),
  16         0b010 => Ok(Special::Code),
  17         0b011 => Err(io::Error::new(
  18             io::ErrorKind::Other,
  19             "Reserved special register",
  20         )),
  21         _ => Err(io::Error::new(
  22             io::ErrorKind::Other,
  23             "Invalid special register",
  24         )),
  25     }
  26 }
  27
  28 fn op1(x: u8) -> Op1 {
  29     match x {
  30         0b000 => Op1::Zero,
  31         0b001 => Op1::Lsl1,
  32         0b010 => Op1::Lsr1,
  33         0b011 => Op1::Asr1,
  34         0b100 => Op1::Incr,
  35         0b101 => Op1::Decr,
  36         0b110 => Op1::Comp,
  37         0b111 => Op1::Negt,
  38         _ => unreachable!(),
  39     }
  40 }
  41
  42 fn op_r(x: u8) -> OpR {
  43     match x & 7 {
  44         0b000 => OpR::Add,
  45         0b001 => OpR::Sub,
  46         0b010 => OpR::And,
  47         0b011 => OpR::Ior,
  48         0b100 => OpR::Xor,
  49         0b101 => OpR::Lsl,
  50         0b110 => OpR::Lsr,
  51         0b111 => OpR::Asr,
  52         _ => unreachable!(),
  53     }
  54 }
  55
  56 fn flag(x: u8) -> bool {
  57     x & 2 != 0
  58 }
  59
  60 fn op_compact(x: u8) -> OpI3 {
  61     match (x >> 3) & 7 {
  62         0b000 => OpI3::Rol,
  63         0b001 => OpI3::Lsl,
  64         0b010 => OpI3::Lsr,
  65         0b011 => OpI3::Asr,
  66         0b100 => OpI3::Clr,
  67         0b101 => OpI3::Set,
  68         0b110 => OpI3::Tog,
  69         0b111 => OpI3::Ext,
  70         _ => unreachable!(),
  71     }
  72 }
  73
  74 impl Decode for Inst {
  75     fn decode(reader: &mut impl Read) -> io::Result<Self> {
  76         use Data::*;
  77         let mut op_byte = [0];
  78         reader.read_exact(&mut op_byte)?;
  79         Ok(match (op_byte[0] >> 3, op_byte[0] & 7) {
  80             (0b0000_0, 0..=2) => Inst::Trap,
  81             (0b0000_0, 0b100) => Inst::Jump(Target::Abs),
  82             (0b0000_0, 0b101) => Inst::Call(Target::Abs),
  83             (0b0000_0, 0b110) => Inst::Jump(Target::Off),
  84             (0b0000_0, 0b111) => Inst::Call(Target::Off),
  85             (0b0000_1, r) => Inst::Swap(reg(r)),
  86             (0b0001_0, r) => Inst::GetR(reg(r)),
  87             (0b0001_1, r) => Inst::SetR(reg(r)),
  88             (0b0010_0, s) => Inst::Get(special(s)?),
  89             (0b0010_1, s) => Inst::Set(special(s)?),
  90             (0b0011_0, o) => Inst::Alu1(op1(o)),
  91             (0b0011_1, r) => Inst::IsLt(reg(r)),
  92             (o @ 0b0100_0..=0b0111_1, r) => Inst::AluR(op_r(o), reg(r)),
  93             (o @ 0b1000_0, r) | (o @ 0b1001_0, r) => Inst::LdD(D1, reg(r), flag(o)),
  94             (o @ 0b1000_1, r) | (o @ 0b1001_1, r) => Inst::StD(D1, reg(r), flag(o)),
  95             (o @ 0b1010_0, r) | (o @ 0b1011_0, r) => Inst::LdD(D2, reg(r), flag(o)),
  96             (o @ 0b1010_1, r) | (o @ 0b1011_1, r) => Inst::StD(D2, reg(r), flag(o)),
  97             (0b1111_0..=0b1111_1, _) => {
  98                 let mut imm_byte = [0];
  99                 reader.read_exact(&mut imm_byte)?;
 100                 let imm = imm_byte[0];
 101                 match op_byte[0] & 0xf {
 102                     0b0000 => Inst::AluI(AluI::And(imm)),
 103                     0b0001 => Inst::AluI(AluI::Ior(imm)),
 104                     0b0010 => Inst::AluI(AluI::Xor(imm)),
 105                     0b0011 => match imm >> 6 {
 106                         0b00 | 0b01 | 0b11 => Inst::AluI(AluI::Add(AddImm::new(imm as i8).unwrap())),
 107                         0b10 => {
 108                             let imm3 = U3::new(imm & 7).unwrap();
 109                             Inst::AluI(AluI::Compact(op_compact(imm), imm3))
 110                         }
 111                         _ => unreachable!(),
 112                     },
 113                     0b0100 => Inst::BEzI(imm as i8),
 114                     0b0101 => Inst::Trap, /* reserved branch */
 115                     0b0110 => Inst::Jump(Target::OffImm(imm as i8)),
 116                     0b0111 => Inst::Call(Target::OffImm(imm as i8)),
 117                     _ => Inst::Trap, /* reserved with immediate */
 118                 }
 119             }
 120             _ => Inst::Trap,
 121         })
 122     }
 123 }