From cf6f353f20eabd73c46bdc83885707b5e4a88abf Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Thu, 17 Sep 2020 18:30:55 -0700
Subject: [PATCH] Change tagging to assume sign extension.

ARM and x86_64 require "real" pointers to be
sign-extended in their top bits. This means
a working pointer is guaranteed to have either "11"
as leading bits, or "00". So, to tag a "fake" pointer
which is an unboxed 32-bit integer, we simply toggle
the leading bit.
---
 code/compiler/13/runtime.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/code/compiler/13/runtime.c b/code/compiler/13/runtime.c
index 7d3b7b2..8e2daf3 100644
--- a/code/compiler/13/runtime.c
+++ b/code/compiler/13/runtime.c
@@ -5,8 +5,8 @@
 #include <stdio.h>
 #include "runtime.h"
 
-#define INT_MARKER (1l << 63)
-#define IS_INT(n) ((uint64_t) n & INT_MARKER)
+#define TOGGLE_MARK(n) ((uint64_t) n ^ ((uint64_t) 1 << 63))
+#define IS_MARKED(n) ((((uint64_t) n) ^ ((uint64_t) n << 1)) & ((uint64_t) 1 << 63))
 
 struct node_base* alloc_node() {
     struct node_base* new_node = malloc(sizeof(struct node_app));
@@ -25,7 +25,7 @@ struct node_app* alloc_app(struct node_base* l, struct node_base* r) {
 }
 
 struct node_num* alloc_num(int32_t n) {
-    return (struct node_num*) (INT_MARKER | n);
+    return (struct node_num*) TOGGLE_MARK(n);
 }
 
 struct node_global* alloc_global(void (*f)(struct gmachine*), int32_t a) {
@@ -50,7 +50,7 @@ void free_node_direct(struct node_base* n) {
 }
 
 void gc_visit_node(struct node_base* n) {
-    if(IS_INT(n) || n->gc_reachable) return;
+    if(IS_MARKED(n) || n->gc_reachable) return;
     n->gc_reachable = 1;
 
     if(n->tag == NODE_APP) {
@@ -170,7 +170,7 @@ void gmachine_split(struct gmachine* g, size_t n) {
 }
 
 struct node_base* gmachine_track(struct gmachine* g, struct node_base* b) {
-    if(IS_INT(b)) return b;
+    if(IS_MARKED(b)) return b;
     g->gc_node_count++;
     b->gc_next = g->gc_nodes;
     g->gc_nodes = b;
@@ -210,7 +210,7 @@ void unwind(struct gmachine* g) {
 
     while(1) {
         struct node_base* peek = stack_peek(s, 0);
-        if(IS_INT(peek)) {
+        if(IS_MARKED(peek)) {
             break;
         } else if(peek->tag == NODE_APP) {
             struct node_app* n = (struct node_app*) peek;
@@ -238,7 +238,7 @@ void unwind(struct gmachine* g) {
 extern void f_main(struct gmachine* s);
 
 void print_node(struct node_base* n) {
-    if(IS_INT(n)) {
+    if(IS_MARKED(n)) {
         printf("%d", (int32_t) n);
     } else if(n->tag == NODE_APP) {
         struct node_app* app = (struct node_app*) n;