asm: allow compound syntax reg operands.

In additon to the encoded notation like t13 and v013f,
we allow forms like (t 19) and (v 1 63) which
mean the same thing.  These are a much more convenient
representation for a compiler.

* share/txr/stdlib/asm.tl (assembler parse-operand): Recognize
a compound expression as an operand, and handle via
parse-compound-operand function.
(parse-compound-operand): New function.

1 files changed, 15 insertions, 0 deletions

diff --git a/share/txr/stdlib/asm.tl b/share/txr/stdlib/asm.tl
index be83a0e3..911f65de 100644
--- a/share/txr/stdlib/asm.tl
+++ b/share/txr/stdlib/asm.tl
@@ -123,6 +123,8 @@
                             ((r rs d ds)
                              (cond
                                ((null arg) 0)
+                               ((consp arg)
+                                (parse-compound-operand arg))
                                ((symbolp arg)
                                 (parse-operand (symbol-name arg)))))
                             (t (error "assembler: invalid arg type spec")))))
@@ -201,6 +203,19 @@
       (and (symbolp obj)
            (not (symbol-package obj)))))
 
+(defun parse-compound-operand (cons)
+  (tree-case cons
+    ((sym arg)
+     (when (<= 0 arg 255)
+       (caseq sym
+         ((t) arg)
+         (d (+ arg 256)))))
+    ((sym arg1 arg2)
+     (when (and (<= 0 arg1 253)
+                (<= 0 arg2 255))
+       (caseq sym
+         (v (+ (* arg1 256) arg2)))))))
+
 (defun parse-operand (str)
   (cond
     ((r^$ #/t[0-9A-Fa-f][0-9A-Fa-f]?/ str)