From 64f4b9192c231236ddeb10548e577ca1e3f40e9b Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Mon, 1 Nov 2021 16:59:01 +0100
Subject: Add support for immediate constants

- Fixnums are tagged with a zero on the LSB.
- The nil value is equal to exactly 1.
- Boolean values have a 11 tag. A value of 111 is true and 011 false.
---
 src/compiler.h | 46 +++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 7 deletions(-)

(limited to 'src/compiler.h')

diff --git a/src/compiler.h b/src/compiler.h
index 3fed075..7d6fa6b 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -5,6 +5,14 @@
 #define PRELUDE_FILE "src/x86_64/prelude.asm"
 #define POSTLUDE_FILE "src/x86_64/postlude.asm"
 
+#define NIL_VAL      1
+#define BOOL_MASK    3
+#define BOOL_TAG     3
+#define BOOL_SHIFT   2
+#define FIXNUM_MASK  1
+#define FIXNUM_TAG   0
+#define FIXNUM_SHIFT 1
+
 void compile_object(Object *obj);
 void compile_fixnum(Object *obj);
 void compile_proc_call(Object *obj);
@@ -26,10 +34,27 @@ emit_file(char *file_name) {
 
 void
 compile_fixnum(Object *obj) {
-    printf("    ;; -- compile_fixnum --\n");
-    printf("    mov     rax, %ld\n", obj->fixnum);
+    printf("    ;; --> compile_fixnum\n");
+    printf("    mov     rax, %ld\n", (obj->fixnum << FIXNUM_SHIFT) | FIXNUM_TAG);
+    printf("    push    rax\n");
+    printf("    ;; <-- compile_fixnum\n");
+}
+
+void
+compile_boolean(Object *obj) {
+    printf("    ;; --> compile_boolean\n");
+    int is_true = obj->type == OBJ_TYPE_TRUE;
+    printf("    mov     rax, %d\n", (is_true << BOOL_SHIFT) | BOOL_TAG);
+    printf("    push    rax\n");
+    printf("    ;; <-- compile_boolean\n");
+}
+
+void
+compile_nil(void) {
+    printf("    ;; --> compile_nil\n");
+    printf("    mov     rax, %d\n", NIL_VAL);
     printf("    push    rax\n");
-    printf("    ;; --------------------\n");
+    printf("    ;; <-- compile_nil\n");
 }
 
 typedef enum OpType {
@@ -42,9 +67,11 @@ typedef enum OpType {
 
 void
 arithmetic_op(OpType type) {
-    printf("    ;; -- arithmetic_op --\n");
+    printf("    ;; --> arithmetic_op\n");
     printf("    pop     rcx\n");
     printf("    pop     rax\n");
+    printf("    sar     rax, %d\n", FIXNUM_SHIFT);
+    printf("    sar     rcx, %d\n", FIXNUM_SHIFT);
     switch (type) {
         case OP_ADD: {
             printf("    add     rax, rcx\n");
@@ -65,13 +92,15 @@ arithmetic_op(OpType type) {
             printf("    mov     rax, rdx\n");
         } break;
     }
+    // No need to add the FIXNUM_TAG here, since it's zero.
+    printf("    sal     rax, %d\n", FIXNUM_SHIFT);
     printf("    push    rax\n");
-    printf("    ;; -------------------\n");
+    printf("    ;; <-- arithmetic_op\n");
 }
 
 void
 compile_proc_call(Object *obj) {
-    printf("    ;; -- compile_proc_call --\n");
+    printf("    ;; --> compile_proc_call\n");
     OpType op;
     if (sv_equal(&obj->head->text, &STRING("+"))) { op = OP_ADD;}
     if (sv_equal(&obj->head->text, &STRING("-"))) { op = OP_SUB;}
@@ -89,12 +118,15 @@ compile_proc_call(Object *obj) {
         args = args->tail;
         arithmetic_op(op);
     }
-    printf("    ;; -----------------------\n");
+    printf("    ;; <-- compile_proc_call\n");
 }
 
 void
 compile_object(Object *obj) {
     switch (obj->type) {
+        case OBJ_TYPE_NIL: { compile_nil(); } break;
+        case OBJ_TYPE_TRUE:
+        case OBJ_TYPE_FALSE: { compile_boolean(obj); } break;
         case OBJ_TYPE_FIXNUM: { compile_fixnum(obj); } break;
         case OBJ_TYPE_PAIR: { compile_proc_call(obj); } break;
         default: break;
-- 
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