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more functions
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@190n
190n committed May 16, 2024
1 parent 6978ef9 commit 63ef7af
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Showing 2 changed files with 132 additions and 100 deletions.
59 changes: 36 additions & 23 deletions src/tail.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -11,12 +11,18 @@ pub const Cpu = struct {
mem: [4096]u8,
code: [4096]Inst,
instructions: usize = 0,
random: std.rand.DefaultPrng,

pub fn init(rom: []const u8) Cpu {
var cpu = Cpu{
.display = undefined,
.mem = undefined,
.code = undefined,
.random = std.rand.DefaultPrng.init(blk: {
var buf: u64 = undefined;
std.posix.getrandom(std.mem.asBytes(&buf)) catch unreachable;
break :blk buf;
}),
};
@memcpy(cpu.mem[0..font_data.len], font_data);
@memset(cpu.mem[font_data.len..0x200], 0);
Expand All @@ -29,20 +35,19 @@ pub const Cpu = struct {

pub fn run(self: *Cpu, instructions: usize) void {
self.instructions = instructions;
self.code[self.pc].func(self, self.code[self.pc].decoded);
self.code[self.pc].func(self, self.code[self.pc].decoded.to());
}
};

const GadgetFunc = *const fn (*Cpu, Decoded) callconv(.Unspecified) void;
const GadgetFunc = *const fn (*Cpu, u32) callconv(.C) void;

pub const Decoded = union {
xy: [2]u4,
xnn: struct { u4, u8 },
nnn: u12,
xyn: [3]u4,

fn from(opcode: u16, cpu: *Cpu, which: enum { xy, xnn, nnn, xyn }) Decoded {
_ = cpu; // autofix
fn decode(opcode: u16, which: enum { xy, xnn, nnn, xyn }) Decoded {
switch (which) {
.xy => {
const x: u4 = @truncate(opcode >> 8);
Expand All @@ -63,14 +68,22 @@ pub const Decoded = union {
},
}
}

pub inline fn from(x: u32) Decoded {
return @as(*const Decoded, @ptrCast(&x)).*;
}

pub inline fn to(self: Decoded) u32 {
return @as(*align(2) const u32, @ptrCast(&self)).*;
}
};

const Inst = struct {
func: GadgetFunc,
decoded: Decoded,
};

fn decode(cpu: *Cpu, decoded: Decoded) void {
fn decode(cpu: *Cpu, decoded: u32) callconv(.C) void {
_ = decoded;

const opcode = std.mem.readInt(u16, cpu.mem[cpu.pc..][0..2], .big);
Expand All @@ -80,16 +93,16 @@ fn decode(cpu: *Cpu, decoded: Decoded) void {
0xEE => .{ .func = &funcs.ret, .decoded = undefined },
else => .{ .func = &invalid, .decoded = undefined },
},
0x1 => .{ .func = &funcs.jump, .decoded = Decoded.from(opcode, cpu, .nnn) },
0x2 => .{ .func = &funcs.call, .decoded = Decoded.from(opcode, cpu, .nnn) },
0x3 => .{ .func = &funcs.skipIfEqual, .decoded = Decoded.from(opcode, cpu, .xnn) },
0x4 => .{ .func = &funcs.skipIfNotEqual, .decoded = Decoded.from(opcode, cpu, .xnn) },
0x1 => .{ .func = &funcs.jump, .decoded = Decoded.decode(opcode, .nnn) },
0x2 => .{ .func = &funcs.call, .decoded = Decoded.decode(opcode, .nnn) },
0x3 => .{ .func = &funcs.skipIfEqual, .decoded = Decoded.decode(opcode, .xnn) },
0x4 => .{ .func = &funcs.skipIfNotEqual, .decoded = Decoded.decode(opcode, .xnn) },
0x5 => switch (opcode & 0xf) {
0x0 => .{ .func = &funcs.skipIfRegistersEqual, .decoded = Decoded.from(opcode, cpu, .xy) },
0x0 => .{ .func = &funcs.skipIfRegistersEqual, .decoded = Decoded.decode(opcode, .xy) },
else => .{ .func = &invalid, .decoded = undefined },
},
0x6 => .{ .func = &funcs.setRegister, .decoded = Decoded.from(opcode, cpu, .xnn) },
0x7 => .{ .func = &funcs.addImmediate, .decoded = Decoded.from(opcode, cpu, .xnn) },
0x6 => .{ .func = &funcs.setRegister, .decoded = Decoded.decode(opcode, .xnn) },
0x7 => .{ .func = &funcs.addImmediate, .decoded = Decoded.decode(opcode, .xnn) },
0x8 => .{
.func = switch (@as(u4, @truncate(opcode))) {
0x0 => &funcs.setRegisterToRegister,
Expand All @@ -103,19 +116,19 @@ fn decode(cpu: *Cpu, decoded: Decoded) void {
0xE => &funcs.shiftLeft,
else => &invalid,
},
.decoded = Decoded.from(opcode, cpu, .xy),
.decoded = Decoded.decode(opcode, .xy),
},
0x9 => switch (opcode & 0xf) {
0x0 => .{ .func = &funcs.skipIfRegistersNotEqual, .decoded = Decoded.from(opcode, cpu, .xy) },
0x0 => .{ .func = &funcs.skipIfRegistersNotEqual, .decoded = Decoded.decode(opcode, .xy) },
else => .{ .func = &invalid, .decoded = undefined },
},
0xA => .{ .func = &funcs.setI, .decoded = Decoded.from(opcode, cpu, .nnn) },
0xB => .{ .func = &funcs.jumpV0, .decoded = Decoded.from(opcode, cpu, .nnn) },
0xC => .{ .func = &funcs.random, .decoded = Decoded.from(opcode, cpu, .xnn) },
0xD => .{ .func = &funcs.draw, .decoded = Decoded.from(opcode, cpu, .xyn) },
0xA => .{ .func = &funcs.setI, .decoded = Decoded.decode(opcode, .nnn) },
0xB => .{ .func = &funcs.jumpV0, .decoded = Decoded.decode(opcode, .nnn) },
0xC => .{ .func = &funcs.random, .decoded = Decoded.decode(opcode, .xnn) },
0xD => .{ .func = &funcs.draw, .decoded = Decoded.decode(opcode, .xyn) },
0xE => switch (opcode & 0xff) {
0x9E => .{ .func = &funcs.skipIfPressed, .decoded = Decoded.from(opcode, cpu, .xnn) },
0xA1 => .{ .func = &funcs.skipIfNotPressed, .decoded = Decoded.from(opcode, cpu, .xnn) },
0x9E => .{ .func = &funcs.skipIfPressed, .decoded = Decoded.decode(opcode, .xnn) },
0xA1 => .{ .func = &funcs.skipIfNotPressed, .decoded = Decoded.decode(opcode, .xnn) },
else => .{ .func = &invalid, .decoded = undefined },
},
0xF => .{
Expand All @@ -133,14 +146,14 @@ fn decode(cpu: *Cpu, decoded: Decoded) void {
0x85 => &funcs.loadFlags,
else => &invalid,
},
.decoded = Decoded.from(opcode, cpu, .xnn),
.decoded = Decoded.decode(opcode, .xnn),
},
};
cpu.code[cpu.pc] = inst;
@call(.always_tail, inst.func, .{ cpu, inst.decoded });
@call(.always_tail, inst.func, .{ cpu, inst.decoded.to() });
}

fn invalid(cpu: *Cpu, decoded: Decoded) void {
fn invalid(cpu: *Cpu, decoded: u32) callconv(.C) void {
_ = decoded; // autofix
std.debug.panic(
"invalid instruction: {x:0>4}",
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