fixing messed up flag calculation

lang/README.md

@@ -624,6 +624,25 @@ main := fn(): uint {
 
 ### Purely Testing Examples
 
+#### nullable_structure
+```hb
+Structure := struct {}
+
+returner_fn := fn(): ?Structure {
+	structure := Structure.()
+	return structure
+}
+
+main := fn(): int {
+	ret := returner_fn()
+	if ret != null {
+		return 1
+	}
+
+	return 0
+}
+```
+
 #### needless_unwrap
 ```hb
 main := fn(): uint {

lang/src/son.rs

@@ -4267,10 +4267,11 @@ impl<'a> Codegen<'a> {
 
         match oty.loc(self.tys) {
             Loc::Reg => {
+                std::println!("{} {} {}", self.ty_display(oty), flag_offset, self.tys.size_of(oty));
                 self.strip_ptr(val);
                 // registers have inverted offsets so that accessing the inner type is a noop
-                let flag_offset = self.tys.size_of(oty) - flag_offset - 1;
-                let fill = self.ci.nodes.new_const(oty, 1i64 << (flag_offset * 8 - 1));
+                let flag_offset = self.tys.size_of(oty) * 8 - flag_offset * 8 - 1;
+                let fill = self.ci.nodes.new_const(oty, 1i64 << flag_offset);
                 val.id = self
                     .ci
                     .nodes
@@ -4595,6 +4596,7 @@ mod tests {
         fb_driver;
 
         // Purely Testing Examples;
+        nullable_structure;
         needless_unwrap;
         inlining_issues;
         null_check_test;

lang/tests/son_tests_nullable_structure.txt

@@ -0,0 +1,21 @@
+main:
+    ADDI64 r254, r254, -16d
+    ST r31, r254, 0a, 16h
+    JAL r31, r0, :returner_fn
+    LI8 r32, 0b
+    ANDI r1, r1, 255d
+    ANDI r32, r32, 255d
+    JEQ r1, r32, :0
+    LI64 r1, 1d
+    JMP :1
+ 0: LI64 r1, 0d
+ 1: LD r31, r254, 0a, 16h
+    ADDI64 r254, r254, 16d
+    JALA r0, r31, 0a
+returner_fn:
+    LD r1, r254, 0a, 0h
+    ORI r1, r1, 128d
+    JALA r0, r31, 0a
+code size: 164
+ret: 1
+status: Ok(())

lang/tests/son_tests_nullable_types.txt

@@ -38,7 +38,7 @@ main:
     JNE r1, r0, :7
     CP r39, r38
     JMP :8
- 7: LI32 r39, 8388609w
+ 7: LI32 r39, 2147483649w
  8: ANDI r39, r39, 4294967295d
     ANDI r38, r38, 4294967295d
     JNE r39, r38, :9