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package j1
import "fmt"
// Decode instruction
func Decode(v uint16) Instruction {
switch {
case v&(1<<15) != 0:
return newLit(v)
case v&(7<<13) == 0:
return newJump(v)
case v&(7<<13) == 1<<13:
return newCond(v)
case v&(7<<13) == 1<<14:
return newCall(v)
case v&(7<<13) == 3<<13:
return newALU(v)
}
return nil
}
// Instruction interface
type Instruction interface {
isInstruction()
}
// Lit is a literal
type Lit uint16
func newLit(v uint16) Lit { return Lit(v &^ uint16(1<<15)) }
func (v Lit) String() string { return fmt.Sprintf("LIT %0.4X", uint16(v)) }
func (v Lit) isInstruction() {}
// Jump is an unconditional branch
type Jump uint16
func newJump(v uint16) Jump { return Jump(v &^ uint16(7<<13)) }
func (v Jump) String() string { return fmt.Sprintf("UBRANCH %0.4X", uint16(v<<1)) }
func (v Jump) isInstruction() {}
// Cond is a conditional branch
type Cond uint16
func newCond(v uint16) Cond { return Cond(v &^ uint16(7<<13)) }
func (v Cond) String() string { return fmt.Sprintf("0BRANCH %0.4X", uint16(v<<1)) }
func (v Cond) isInstruction() {}
// Call procedure
type Call uint16
func newCall(v uint16) Call { return Call(v &^ uint16(7<<13)) }
func (v Call) String() string { return fmt.Sprintf("CALL %0.4X", uint16(v<<1)) }
func (v Call) isInstruction() {}
// ALU instruction
type ALU struct {
Opcode uint16
RtoPC bool
TtoN bool
TtoR bool
NtoAtT bool
Rdir int8
Ddir int8
}
func newALU(v uint16) ALU {
return ALU{
Opcode: (v >> 8) & 15,
RtoPC: v&(1<<12) != 0,
TtoN: v&(1<<7) != 0,
TtoR: v&(1<<6) != 0,
NtoAtT: v&(1<<5) != 0,
Rdir: expand((v >> 2) & 3),
Ddir: expand(v & 3),
}
}
func (v ALU) isInstruction() {}
func expand(v uint16) int8 {
if v&2 != 0 {
v |= 0xfc
}
return int8(v)
}
const (
opT = iota // 0
opN // 1
opTplusN // 2
opTandN // 3
opTorN // 4
opTxorN // 5
opNotT // 6
opNeqT // 7
opNleT // 8
opNrshiftT // 9
opTminus1 // 10
opR // 11
opAtT // 12
opNlshiftT // 13
opDepth // 14
opNuleT // 15
)
var opcodes = []string{
"T", "N", "T+N", "T&N", "T|N", "T^N", "~T", "N==T",
"N<T", "N>>T", "T-1", "R", "[T]", "N<<T", "depth", "Nu<T",
}
func (v ALU) String() string {
s := "ALU " + opcodes[v.Opcode]
if v.RtoPC {
s += " R→PC"
}
if v.TtoN {
s += " T→N"
}
if v.TtoR {
s += " T→R"
}
if v.NtoAtT {
s += " N→[T]"
}
if v.Rdir != 0 {
s += fmt.Sprintf(" r%+d", v.Rdir)
}
if v.Ddir != 0 {
s += fmt.Sprintf(" d%+d", v.Ddir)
}
return s
}
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