finish impl for ConstantLong

src/chunk.zig

@@ -15,26 +15,26 @@ pub const OpCode = AllOpcodes{};
 fn simpleInstruction(
     stdout: var,
     comptime name: []const u8,
-    offset: usize,
+    index: usize,
 ) !usize {
     try stdout.print("{}\n", name);
-    return offset + 1;
+    return index + 1;
 }
 
 fn constantInstruction(
     stdout: var,
     comptime name: []const u8,
     chunk: *Chunk,
-    offset: usize,
+    index: usize,
 ) !usize {
     // get the constant's index in constants slice
-    var idx = chunk.code[offset + 1];
+    var idx = chunk.code[index + 1];
 
     try stdout.print("\t{}\t{} '", name, idx);
     try value.printValue(stdout, chunk.constants.values[idx]);
     try stdout.print("'\n");
 
-    return offset + 2;
+    return index + 2;
 }
 
 fn constantLongInstruction(
@@ -43,24 +43,19 @@ fn constantLongInstruction(
     chunk: *Chunk,
     offset: usize,
 ) !usize {
-    // get the constant's index in constants slice
-    var v0: u8 = chunk.code[offset + 3];
-    var v1: u8 = chunk.code[offset + 2];
-    var v2: u8 = chunk.code[offset + 1];
+    // constantLong uses three u8's that encode a u24 as the
+    // contants' index.
+    var v3: u8 = chunk.code[offset + 1];
+    var v2: u8 = chunk.code[offset + 2];
+    var v1: u8 = chunk.code[offset + 3];
 
-    // TODO: this does not work. just decreased first term
-    // to fix a compile error.
-
-    // we should also move the actual printing into its own
-    // function too since constantInstruction and
-    // constantLongInstruction share code.
-    var idx: u24 = (v2 << 4) | (v1 << 7) | v0;
+    var idx: u24 = (@intCast(u24, v3) << 16) | (@intCast(u24, v2) << 8) | v1;
 
     try stdout.print("\t{}\t{} '", name, idx);
     try value.printValue(stdout, chunk.constants.values[idx]);
     try stdout.print("'\n");
 
-    return offset + 2;
+    return offset + 4;
 }
 
 pub const Chunk = struct {
@@ -112,13 +107,18 @@ pub const Chunk = struct {
             try self.write(OpCode.Constant, line);
             try self.write(@intCast(u8, constant_idx), line);
         } else {
-            // TODO: convert the usize to u24, and from
-            // u24, split it into three u8's.
+            var idx_u24: u24 = @intCast(u24, constant_idx);
 
-            // also convert from u8 back to u24.
-            // i know that we can do from two u8's to go to a u16
-            // with (v1 << 7) | v0.
-            try self.write(0, line);
+            const mask = @intCast(u24, 0xff);
+
+            const v1: u8 = @intCast(u8, idx_u24 & mask);
+            const v2: u8 = @intCast(u8, (idx_u24 >> 8) & mask);
+            const v3: u8 = @intCast(u8, (idx_u24 >> 16) & mask);
+
+            try self.write(OpCode.ConstantLong, line);
+            try self.write(v3, line);
+            try self.write(v2, line);
+            try self.write(v1, line);
         }
     }
 

src/main.zig

@@ -115,7 +115,10 @@ pub fn main() !void {
     //var opcode_byte: u8 = @enumToInt(chunk.OpCode.Return);
     //try chk.write(chunk.OpCode.Return);
 
-    var constant = try chk.writeConstant(1.2, 123);
+    var i: usize = 0;
+    while (i < 260) : (i += 1) {
+        var constant = try chk.writeConstant(1.2, 123);
+    }
     try chk.write(chunk.OpCode.Return, 123);
 
     try chk.disassemble(stdout, "test chunk");