Added ?DUP

[jonesforth.git] / jonesforth.S

diff --git a/jonesforth.S b/jonesforth.S
index 5c1249c..be0420a 100644 (file)
--- a/jonesforth.S
+++ b/jonesforth.S
@@ -1,11 +1,11 @@
 /*     A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
        By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
        This is PUBLIC DOMAIN (see public domain release statement below).
-       $Id: jonesforth.S,v 1.36 2007-09-27 23:09:39 rich Exp $
+       $Id: jonesforth.S,v 1.37 2007-09-28 18:55:10 rich Exp $
 
        gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S
 */
-       .set JONES_VERSION,36
+       .set JONES_VERSION,37
 /*
        INTRODUCTION ----------------------------------------------------------------------
 
@@ -757,6 +757,14 @@ code_\label :                      // assembler code follows
        push %ecx
        NEXT
 
+       defcode "?DUP",4,,QDUP  // duplicate top of stack if non-zero
+       pop %eax
+       test %eax,%eax
+       jz 1f
+       push %eax
+1:     push %eax
+       NEXT
+
        defcode "1+",2,,INCR
        incl (%esp)             // increment top of stack
        NEXT
@@ -1924,10 +1932,13 @@ _COMMA:
        NEXT
 
 /*
-       PRINTING STRINGS ----------------------------------------------------------------------
+       LITERAL STRINGS ----------------------------------------------------------------------
+
+       LITSTRING is a primitive used to implement the ." and S" operators (which are written in
+       FORTH).  See the definition of those operators later.
 
-       LITSTRING and EMITSTRING are primitives used to implement the ." and S" operators
-       (which are written in FORTH).  See the definition of those operators below.
+       TELL just prints a string.  It's more efficient to define this in assembly because we
+       can make it a single Linux syscall.
 */
 
        defcode "LITSTRING",9,,LITSTRING
@@ -1939,7 +1950,7 @@ _COMMA:
        andl $~3,%esi
        NEXT
 
-       defcode "EMITSTRING",10,,EMITSTRING
+       defcode "TELL",4,,TELL
        mov $1,%ebx             // 1st param: stdout
        pop %edx                // 3rd param: length of string
        pop %ecx                // 2nd param: address of string