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 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

(limited to 'compiler.scm')

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"))))
-- 
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