494 lines
9 KiB
Swift
494 lines
9 KiB
Swift
//
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// Nga.swift
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//
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// Nga is the virtual machine at the heart
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// of RETRO. It provides a MISC based dual
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// stack processor that's capable of hosting
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// RETRO or other environments.
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//
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// This is a reimplementation in Swift. I've
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// held off doing this until now, but as I
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// plan to continue using Apple computers and
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// iPads, it's becoming clear that they see
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// this as the future, and it'll become more
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// difficult to justify holding out on
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// Objective-C going forward.
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//
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// So here we go...
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//
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// Copyright 2020, Charles Childers
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//
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import Foundation
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// Limits
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let imageSize: Int = 512000
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let stackSize: Int = 2048
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let CELLMAX = Int64.max - 1
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let CELLMIN = Int64.min
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// Notes:
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// While Nga is designed as a 32-bit system,
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// this implementation is 64-bit internally
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// to allow greater numeric range.
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// I'm adding some extensions to existing types
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// for easier access to individual characters
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// in strings and bytes in integers.
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extension StringProtocol {
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var asciiValues: [UInt8] { compactMap(\.asciiValue) }
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}
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extension FixedWidthInteger where Self: SignedInteger {
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var bytes: [Int8] {
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var _endian = littleEndian
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let bytePtr = withUnsafePointer(to: &_endian) {
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$0.withMemoryRebound(to: Int8.self, capacity: MemoryLayout<Self>.size) {
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UnsafeBufferPointer(start: $0, count: MemoryLayout<Self>.size)
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}
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}
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return [Int8](bytePtr)
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}
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}
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// I implement a stack class here for handling
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// the details of the stacks. Stacks in Nga are
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// LIFO, holding only signed integer values.
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class Stack {
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private var data = [Int64](repeating: 0, count: stackSize)
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private var sp: Int = 0
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public func tos() -> Int64 {
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return data[sp]
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}
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public func nos() -> Int64 {
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return data[sp - 1]
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}
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public func push(_ n: Int64) {
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sp += 1
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data[sp] = n
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}
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public func pop() -> Int64 {
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let v = data[sp]
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data[sp] = 0
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sp -= 1
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return v
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}
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public func drop() {
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data[sp] = 0
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sp -= 1
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}
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public func swap() {
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let a = tos()
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let b = nos()
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data[sp] = b
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data[sp - 1] = a
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}
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public func depth() -> Int {
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return sp
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}
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public func item(_ n: Int) -> Int64 {
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return data[n]
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}
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}
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// Instruction Pointer and Memory
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// I'm adding some extra padding at EOM for now.
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// This may be changed in the future.
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var ip: Int = 0
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var memory = [Int64](repeating: 0, count: imageSize + 1024)
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// Create the stacks
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var data = Stack()
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var address = Stack()
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// Now, I implement the instructions. Each gets
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// a dedicated function.
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func inst_no() {
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}
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func inst_li() {
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ip += 1
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data.push(memory[ip])
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}
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func inst_du() {
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data.push(data.tos())
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}
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func inst_dr() {
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data.drop()
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}
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func inst_sw() {
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data.swap()
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}
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func inst_pu() {
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address.push(data.pop())
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}
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func inst_po() {
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data.push(address.pop())
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}
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func inst_ju() {
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ip = Int(data.pop() - 1)
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}
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func inst_ca() {
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address.push(Int64(ip))
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ip = Int(data.pop() - 1)
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}
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func inst_cc() {
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let dest = data.pop()
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let flag = data.pop()
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if (flag != 0) {
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address.push(Int64(ip))
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ip = Int(dest - 1)
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}
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}
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func inst_re() {
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ip = Int(address.pop())
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}
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func inst_eq() {
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let tos = data.pop()
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let nos = data.pop()
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data.push((nos == tos) ? -1 : 0)
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}
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func inst_ne() {
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let tos = data.pop()
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let nos = data.pop()
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data.push((nos != tos) ? -1 : 0)
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}
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func inst_lt() {
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let tos = data.pop()
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let nos = data.pop()
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data.push((nos < tos) ? -1 : 0)
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}
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func inst_gt() {
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let tos = data.pop()
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let nos = data.pop()
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data.push((nos > tos) ? -1 : 0)
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}
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func inst_fe() {
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let target = data.pop()
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switch (target) {
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case -1:
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data.push(Int64(data.depth()))
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case -2:
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data.push(Int64(address.depth()))
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case -3:
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data.push(Int64(imageSize))
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case -4:
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data.push(CELLMIN)
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case -5:
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data.push(CELLMAX)
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default:
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data.push(memory[Int(target)])
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}
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}
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func inst_st() {
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let addr = data.pop()
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let value = data.pop()
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memory[Int(addr)] = value;
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}
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func inst_ad() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(nos + tos)
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}
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func inst_su() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(nos - tos)
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}
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func inst_mu() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(nos * tos)
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}
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func inst_di() {
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let a = data.pop()
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let b = data.pop()
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data.push(b % a)
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data.push(b / a)
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}
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func inst_an() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(tos & nos)
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}
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func inst_or() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(nos | tos)
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}
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func inst_xo() {
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let tos = data.pop()
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let nos = data.pop()
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data.push(nos ^ tos)
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}
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func inst_sh() {
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let tos = data.pop()
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let nos = data.pop()
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if (tos < 0) {
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data.push(nos << (tos * -1))
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}
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else {
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if (nos < 0 && tos > 0) {
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data.push(nos >> tos | ~(~0 >> tos))
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}
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else {
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data.push(nos >> tos)
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}
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}
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}
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func inst_zr() {
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if (data.tos() == 0) {
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data.drop()
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ip = Int(address.pop())
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}
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}
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func inst_ha() {
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ip = imageSize;
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}
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func inst_ie() {
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data.push(1)
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}
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func inst_iq() {
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data.drop()
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data.push(0)
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data.push(0)
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}
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func inst_ii() {
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data.drop()
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let v = UnicodeScalar(Int(data.pop())) ?? UnicodeScalar(32)
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print(Character(v!), terminator: "")
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}
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// With those done, I turn to handling the
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// instructions.
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// In C, I use a jump table for this. I don't
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// know how to do this in Swift.
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func ngaProcessOpcode(opcode: Int64) {
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switch opcode {
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case 0:
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()
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case 1:
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inst_li()
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case 2:
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inst_du()
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case 3:
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inst_dr()
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case 4:
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inst_sw()
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case 5:
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inst_pu()
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case 6:
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inst_po()
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case 7:
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inst_ju()
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case 8:
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inst_ca()
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case 9:
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inst_cc()
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case 10:
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inst_re()
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case 11:
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inst_eq()
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case 12:
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inst_ne()
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case 13:
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inst_lt()
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case 14:
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inst_gt()
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case 15:
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inst_fe()
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case 16:
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inst_st()
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case 17:
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inst_ad()
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case 18:
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inst_su()
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case 19:
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inst_mu()
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case 20:
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inst_di()
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case 21:
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inst_an()
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case 22:
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inst_or()
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case 23:
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inst_xo()
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case 24:
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inst_sh()
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case 25:
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inst_zr()
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case 26:
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inst_ha()
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case 27:
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inst_ie()
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case 28:
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inst_iq()
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case 29:
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inst_ii()
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default:
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inst_ha()
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}
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}
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// Each opcode can have up to four instructions
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// This validates them, letting us know if it's
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// safe to run them.
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func ngaValidatePackedOpcodes(_ opcode: Int64) -> Bool {
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var valid = true
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for inst in Int32(opcode).bytes {
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if !(inst >= 0 && inst <= 29) {
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valid = false
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}
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}
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return valid
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}
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// This will process an opcode bundle
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func ngaProcessPackedOpcodes(_ opcode: Int64) {
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for inst in Int32(opcode).bytes {
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ngaProcessOpcode(opcode: Int64(inst))
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}
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}
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// For debugging purposes
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func dump() {
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for i in 0 ... data.depth() {
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if i == data.depth() {
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print("TOS")
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}
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print(Int(data.item(i)))
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}
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}
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// Interfacing
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func extractString(at: Int) -> String {
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var s: String = ""
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var next = at
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while memory[next] != 0 {
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let value = Int(memory[next])
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let u = UnicodeScalar(value)
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let char = Character(u!)
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s.append(char)
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next += 1
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}
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return s
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}
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func injectString(_ s: String, to: Int) {
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var i: Int = 0
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for ch in s.asciiValues {
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let n = Int64(ch)
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memory[to + i] = n
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memory[to + i + 1] = 0
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i += 1
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}
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}
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// Run through an image, quiting when EOM
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// is reached
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func execute(_ word: Int) {
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address.push(0)
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ip = word
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while ip < imageSize {
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// print("ip:", ip, "bundle", memory[ip], "insts", Int32(memory[ip]).bytes)
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let opcode = memory[ip]
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if ngaValidatePackedOpcodes(opcode) {
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ngaProcessPackedOpcodes(opcode)
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} else {
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print("Error: invalid opcode")
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ip = imageSize
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}
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ip += 1
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if address.depth() == 0 {
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ip = imageSize
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}
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}
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}
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func process() {
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ip = 0
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while ip < imageSize - 1 {
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ngaProcessPackedOpcodes(memory[ip])
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ip += 1
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}
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}
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// Tests
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loadImage()
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// Display the dictionary
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var i = memory[2]
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var interpret: Int = 0
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while i != 0 {
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let name = extractString(at: Int(i + 3))
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// print(name)
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if name == "interpret" {
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interpret = Int(memory[Int(i) + 1])
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}
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i = memory[Int(i)]
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}
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var done = false
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print("RETRO (using nga.swift)")
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while !done {
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let code = readLine()
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if code == "bye" {
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done = true
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} else {
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injectString(code ?? "()", to: Int(memory[7]))
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data.push(memory[7])
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execute(interpret)
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}
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}
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dump()
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