ALLOT, +!, -!

[rrq/jonesforth.git] / jonesforth.S

diff --git a/jonesforth.S b/jonesforth.S
index 11b0cfd163b46a8b2fa5bdae4424ca3a405a2619..e82bd1fc921d2fab5d62418af34daed0dd7c2fd7 100644 (file)
--- a/jonesforth.S
+++ b/jonesforth.S
@@ -1,4 +1,4 @@
-/* A minimal FORTH interpreter for Linux / i386 systems. -*- asm -*-
+/* A somewhat minimal FORTH interpreter for Linux / i386 systems. -*- asm -*-

  * By Richard W.M. Jones <rich@annexia.org>
  *
  * gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S
  * By Richard W.M. Jones <rich@annexia.org>
  *
  * gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S


@@ -317,9 +317,22 @@ var_\name :
        push %eax               // push value onto stack
        NEXT
 
        push %eax               // push value onto stack
        NEXT
 

+       defcode "+!",2,ADDSTORE
+       pop %ebx                // address
+       pop %eax                // the amount to add
+       addl %eax,(%ebx)        // add it
+       NEXT
+
+       defcode "-!",2,SUBSTORE
+       pop %ebx                // address
+       pop %eax                // the amount to subtract
+       subl %eax,(%ebx)        // add it
+       NEXT
+

 /* ! and @ (STORE and FETCH) store 32-bit words.  It's also useful to be able to read and write bytes.
  * I don't know whether FORTH has these words, so I invented my own, called !b and @b.
  * Byte-oriented operations only work on architectures which permit them (i386 is one of those).
 /* ! and @ (STORE and FETCH) store 32-bit words.  It's also useful to be able to read and write bytes.
  * I don't know whether FORTH has these words, so I invented my own, called !b and @b.
  * Byte-oriented operations only work on architectures which permit them (i386 is one of those).

+ * UPDATE: writing a byte to the dictionary pointer is called C, in FORTH.

  */
        defcode "!b",2,,STOREBYTE
        pop %ebx                // address to store at
  */
        defcode "!b",2,,STOREBYTE
        pop %ebx                // address to store at


@@ -930,7 +943,7 @@ buffer:
                        DUP '\"' <>
                WHILE
                        HERE @ !b       \\ store the character in the compiled image
                        DUP '\"' <>
                WHILE
                        HERE @ !b       \\ store the character in the compiled image

-                       HERE @ 1+ HERE ! \\ increment HERE pointer by 1 byte
+                       HERE 1 +!       \\ increment HERE pointer by 1 byte

                REPEAT
                DROP            \\ drop the double quote character at the end
                DUP             \\ get the saved address of the length word
                REPEAT
                DROP            \\ drop the double quote character at the end
                DUP             \\ get the saved address of the length word


@@ -969,6 +982,10 @@ buffer:
        ,               \\ compile it
 ;
 
        ,               \\ compile it
 ;
 

+\\ ALLOT is used to allocate (static) memory when compiling.  It increases HERE by
+\\ the amount given on the stack.
+: ALLOT HERE +! ;
+

 
 \\ Finally print the welcome prompt.
 .\" OK \"
 
 \\ Finally print the welcome prompt.
 .\" OK \"