make in-memory instruction a little nicer to work with

1 files changed, 35 insertions, 33 deletions

diff --git a/src/codegen.zig b/src/codegen.zig
index 8c3f592..7ade3fd 100644
--- a/src/codegen.zig
+++ b/src/codegen.zig
@@ -22,7 +22,7 @@ const Register = enum(u5) {
 };
 
 /// TODO: Panic on calls that become reserved hints, e.g. addw with rd=x0
-const Instruction = packed union {
+const Instruction = union(enum) {
     r: R,
     i: I,
     s: S,
@@ -199,7 +199,7 @@ const Instruction = packed union {
         rd: Register,
         funct3: u3,
         rs1: Register,
-        imm: u12,
+        imm: i12,
 
         fn init(opcode: Opcode, rd: Register, funct3: u3, rs1: Register, imm: i12) Self {
             return .{ .i = .{
@@ -207,7 +207,7 @@ const Instruction = packed union {
                 .rd = rd,
                 .funct3 = funct3,
                 .rs1 = rs1,
-                .imm = @bitCast(imm),
+                .imm = imm,
             } };
         }
     };
@@ -327,17 +327,16 @@ const Instruction = packed union {
         funct3: u3,
         rs1: Register,
         rs2: Register,
-        imm11_5: u7,
+        imm11_5: i7,
 
         fn init(opcode: Opcode, funct3: u3, rs1: Register, rs2: Register, imm: i12) Self {
-            const umm: u12 = @bitCast(imm);
             return .{ .s = .{
                 .opcode = opcode,
-                .imm4_0 = @truncate(umm),
+                .imm4_0 = @intCast(imm & 0xf),
                 .funct3 = funct3,
                 .rs1 = rs1,
                 .rs2 = rs2,
-                .imm11_5 = @truncate(umm >> 5),
+                .imm11_5 = @intCast(imm >> 5),
             } };
         }
     };
@@ -371,20 +370,19 @@ const Instruction = packed union {
         rs1: Register,
         rs2: Register,
         imm10_5: u6,
-        imm12: u1,
+        imm12: i1,
 
         fn init(opcode: Opcode, funct3: u3, rs1: Register, rs2: Register, imm: i13) Self {
             std.debug.assert(imm & 1 == 0);
-            const umm: u13 = @bitCast(imm);
             return .{ .b = .{
                 .opcode = opcode,
-                .imm11 = @truncate(umm >> 11),
-                .imm4_1 = @truncate(umm >> 1),
+                .imm11 = @intCast((imm >> 11) & 1),
+                .imm4_1 = @intCast((imm >> 1) & 0xf),
                 .funct3 = funct3,
                 .rs1 = rs1,
                 .rs2 = rs2,
-                .imm10_5 = @truncate(umm >> 5),
-                .imm12 = @truncate(umm >> 12),
+                .imm10_5 = @intCast((imm >> 5) & 0x3f),
+                .imm12 = @intCast(imm >> 12),
             } };
         }
     };
@@ -440,13 +438,13 @@ const Instruction = packed union {
     const U = packed struct(u32) {
         opcode: Opcode,
         rd: Register,
-        imm12_31: u20,
+        imm12_31: i20,
 
         fn init(opcode: Opcode, rd: Register, imm: i20) Self {
             return .{ .u = .{
                 .opcode = opcode,
                 .rd = rd,
-                .imm12_31 = @bitCast(imm),
+                .imm12_31 = imm,
             } };
         }
     };
@@ -467,18 +465,17 @@ const Instruction = packed union {
         imm12_19: u8,
         imm11: u1,
         imm1_10: u10,
-        imm20: u1,
+        imm20: i1,
 
         fn init(opcode: Opcode, rd: Register, imm: i21) Self {
             std.debug.assert(imm & 1 == 0);
-            const umm: u21 = @bitCast(imm);
             return .{ .j = .{
                 .opcode = opcode,
                 .rd = rd,
-                .imm12_19 = @truncate(umm >> 12),
-                .imm11 = @truncate(umm >> 11),
-                .imm1_10 = @truncate(umm >> 1),
-                .imm20 = @intCast(umm >> 20),
+                .imm12_19 = @intCast((imm >> 12) & 0xff),
+                .imm11 = @intCast((imm >> 11) & 1),
+                .imm1_10 = @intCast((imm >> 1) & 0x3ff),
+                .imm20 = @intCast(imm >> 20),
             } };
         }
     };
@@ -488,6 +485,12 @@ const Instruction = packed union {
         return J.init(0b1101111, rd, imm);
     }
 
+    fn encode(self: Self) u32 {
+        return switch (self) {
+            inline else => |s| @bitCast(s),
+        };
+    }
+
     const Self = @This();
 };
 
@@ -820,21 +823,20 @@ pub fn create_elf(allocator: Allocator, proc: compile.Procedure) ![]u8 {
     // TODO: make this less sheiße
     for (ctx.relocations.items) |relocation| {
         const instr = &ctx.instructions.items[relocation.instr];
-        const opcode: Instruction.Opcode = @truncate(@as(u32, @bitCast(instr.*)));
         const target: isize = @intCast(ctx.block_starts.items[@intFromEnum(relocation.target)]);
         const from: isize = @intCast(relocation.instr);
-        switch (opcode) {
-            0b1101111 => {
-                const jal: Instruction.J = instr.j;
-                instr.* = .jal(jal.rd, @intCast((target - from) * 4));
+        switch (instr.*) {
+            .j => |j| {
+                if (j.opcode == 0b1101111) {
+                    instr.* = .jal(j.rd, @intCast((target - from) * 4));
+                } else std.debug.panic("Not yet implemented instruction with relocation {}\n", .{instr});
             },
-            0b1100011 => {
-                const b: Instruction.B = instr.b;
-                if (b.funct3 != 0)
-                    std.debug.panic("Not yet implemented instruction with relocation\n", .{});
-                instr.* = .beq(b.rs1, b.rs2, @intCast((target - from) * 4));
+            .b => |b| {
+                if (b.opcode == 0b1100011 and b.funct3 == 0) {
+                    instr.* = .beq(b.rs1, b.rs2, @intCast((target - from) * 4));
+                } else std.debug.panic("Not yet implemented instruction with relocation {}\n", .{instr});
             },
-            else => std.debug.panic("Not yet implemented instruction with relocation\n", .{}),
+            else => std.debug.panic("Not yet implemented instruction with relocation {}\n", .{instr}),
         }
     }
 
@@ -845,7 +847,7 @@ pub fn create_elf(allocator: Allocator, proc: compile.Procedure) ![]u8 {
     try output_buffer.appendNTimes(undefined, @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr));
     const output = output_buffer.writer();
     for (ctx.instructions.items) |instr| {
-        try output.writeInt(u32, @bitCast(instr), .little);
+        try output.writeInt(u32, instr.encode(), .little);
     }
 
     const base_addr = 0x10000000;