From 9f65c417b7575eab5ebd2733a817a0f0e954c4d9 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson@vistahigherlearning.com>
Date: Wed, 10 Aug 2022 18:49:33 -0400
Subject: Step 2: Immediate Constants

---
 compiler.scm | 19 ++++++++++++++++++-
 test.c       | 27 ++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/compiler.scm b/compiler.scm
index 1285ac6..919be4c 100644
--- a/compiler.scm
+++ b/compiler.scm
@@ -5,6 +5,23 @@
   (newline))
 
 (define (compile-program x)
+  (define fixnum-shift 2)
+  (define fixnum-tag 0)
+  (define char-shift 8)
+  (define char-tag 15)
+  (define boolean-shift 7)
+  (define boolean-tag 31)
+  (define empty-list 47) ;; #b00101111
+  (define (immediate-rep x)
+    (cond
+     ((integer? x)
+      (ash x fixnum-shift))
+     ((char? x)
+      (logior (ash (char->integer x) char-shift) char-tag))
+     ((boolean? x)
+      (logior (ash (if x 1 0) boolean-shift) boolean-tag))
+     ((null? x)
+      empty-list)))
   (with-output-to-file "scheme_entry.S"
     (lambda ()
       (display ".text
@@ -13,5 +30,5 @@
 .type	scheme_entry, @function
 scheme_entry:
 ")
-      (emit "movl $~a, %eax" x)
+      (emit "movl $~a, %eax" (immediate-rep x))
       (emit "ret"))))
diff --git a/test.c b/test.c
index 2d814e0..f41ae64 100644
--- a/test.c
+++ b/test.c
@@ -1,6 +1,31 @@
 #include <stdio.h>
 
+#define fixnum_mask 3
+#define fixnum_tag 0
+#define fixnum_shift 2
+#define char_mask 255
+#define char_shift 8
+#define char_tag 15
+#define boolean_mask 127
+#define boolean_shift 7
+#define boolean_tag 31
+#define empty_list 47
+
 int main(int argc, char** argv) {
-  printf("%d\n", scheme_entry());
+  int val = scheme_entry();
+
+  if((val & fixnum_mask) == fixnum_tag) {
+    printf("%d\n", val >> fixnum_shift);
+  } else if((val & char_mask) == char_tag) {
+    printf("%c\n", val >> char_shift);
+  } else if((val & boolean_mask) == boolean_tag) {
+    if((val >> boolean_shift) == 1) {
+      printf("#t\n");
+    } else {
+      printf("#f\n");
+    }
+  } else if(val == empty_list) {
+    printf("()\n");
+  }
   return 0;
 }
-- 
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