diff --git a/vvp/README.txt b/vvp/README.txt
index bdb9882db..a469e0530 100644
--- a/vvp/README.txt
+++ b/vvp/README.txt
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
  *
- *  $Id: README.txt,v 1.26 2001/06/05 03:05:41 steve Exp $
+ *  $Id: README.txt,v 1.27 2001/06/07 03:09:03 steve Exp $
  */
 
 VVP SIMULATION ENGINE
@@ -405,6 +405,7 @@ functors. These operators are not in general bitwise, so special
 measures are needed to make them work in a functor environment. We
 create special statement types for the various arithmetic operators.
 
+	<label> .arith/sub  <wid>, <symbols_list>;
 	<label> .arith/sum  <wid>, <symbols_list>;
 
 Addition is represented by the .arith/sum statement. This creates an
@@ -416,6 +417,8 @@ The sum can add together up to 4 operands, specified in the
 (lsb first) are listed, then the bits of the second, and so on. The
 number of symbols must be an even multiple of the width of the operator.
 
+Subtraction is similar to addition, except that the 2nd, 3rd and 4th
+vectors are subtracted from the first.
 
 THREAD STATEMENTS:
 
diff --git a/vvp/arith.cc b/vvp/arith.cc
index b8098a07b..67c372ca4 100644
--- a/vvp/arith.cc
+++ b/vvp/arith.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: arith.cc,v 1.1 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: arith.cc,v 1.2 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  "arith.h"
@@ -26,12 +26,12 @@
 
 # include  <stdio.h>
 
-vvp_arith_sum::vvp_arith_sum(vvp_ipoint_t b, unsigned w)
+vvp_arith_::vvp_arith_(vvp_ipoint_t b, unsigned w)
 : base_(b), wid_(w)
 {
 }
 
-void vvp_arith_sum::output_x_(bool push)
+void vvp_arith_::output_x_(bool push)
 {
       for (unsigned idx = 0 ;  idx < wid_ ;  idx += 1) {
 	    vvp_ipoint_t ptr = ipoint_index(base_,idx);
@@ -48,6 +48,11 @@ void vvp_arith_sum::output_x_(bool push)
       }
 }
 
+vvp_arith_sum::vvp_arith_sum(vvp_ipoint_t b, unsigned w)
+: vvp_arith_(b, w)
+{
+}
+
 void vvp_arith_sum::set(vvp_ipoint_t i, functor_t f, bool push)
 {
       assert(wid_ <= sizeof(unsigned long));
@@ -96,8 +101,64 @@ void vvp_arith_sum::set(vvp_ipoint_t i, functor_t f, bool push)
       }
 }
 
+vvp_arith_sub::vvp_arith_sub(vvp_ipoint_t b, unsigned w)
+: vvp_arith_(b, w)
+{
+}
+
+void vvp_arith_sub::set(vvp_ipoint_t i, functor_t f, bool push)
+{
+      assert(wid_ <= sizeof(unsigned long));
+
+      unsigned long sum = 0;
+
+      for (unsigned idx = 0 ;  idx < wid_ ;  idx += 1) {
+	    vvp_ipoint_t ptr = ipoint_index(base_,idx);
+	    functor_t obj = functor_index(ptr);
+
+	    unsigned ival = obj->ival;
+	    if (ival & 0xaa) {
+		  output_x_(push);
+		  return;
+	    }
+
+	    unsigned tmp = 0;
+	    if (ival & 0x01)
+		  tmp += 1;
+	    if (ival & 0x04)
+		  tmp -= 1;
+	    if (ival & 0x10)
+		  tmp -= 1;
+	    if (ival & 0x40)
+		  tmp -= 1;
+
+	    sum += (tmp << idx);
+      }
+	    
+      for (unsigned idx = 0 ;  idx < wid_ ;  idx += 1) {
+	    vvp_ipoint_t ptr = ipoint_index(base_,idx);
+	    functor_t obj = functor_index(ptr);
+
+	    unsigned oval = sum & 1;
+	    sum >>= 1;
+
+	    if (obj->oval == oval)
+		  continue;
+
+
+	    obj->oval = oval;
+	    if (push)
+		  functor_propagate(ptr);
+	    else
+		  schedule_functor(ptr, 0);
+      }
+}
+
 /*
  * $Log: arith.cc,v $
+ * Revision 1.2  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.1  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *
diff --git a/vvp/arith.h b/vvp/arith.h
index e5d19f4cd..4cc0e9a16 100644
--- a/vvp/arith.h
+++ b/vvp/arith.h
@@ -19,36 +19,63 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: arith.h,v 1.1 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: arith.h,v 1.2 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  "functor.h"
 
+class vvp_arith_  : public vvp_fobj_s {
+
+    public:
+      explicit vvp_arith_(vvp_ipoint_t b, unsigned wid);
+
+    protected:
+      vvp_ipoint_t base_;
+      unsigned wid_;
+
+    protected:
+      void output_x_(bool push);
+
+    private: // not implemented
+      vvp_arith_(const vvp_arith_&);
+      vvp_arith_& operator= (const vvp_arith_&);
+};
+
+
 /*
  * This class is a mode-42 object for arithmetic sum. Inputs that come
  * in cause the 4-input summation to be calculated, and output
  * functors that are affected cause propagations.
  */
-class vvp_arith_sum  : public vvp_fobj_s {
+class vvp_arith_sum  : public vvp_arith_ {
 
     public:
       explicit vvp_arith_sum(vvp_ipoint_t b, unsigned wid);
 
       void set(vvp_ipoint_t i, functor_t f, bool push);
 
-    private:
-      vvp_ipoint_t base_;
-      unsigned wid_;
-
-      void output_x_(bool push);
-
     private: // not implemented
       vvp_arith_sum(const vvp_arith_sum&);
       vvp_arith_sum& operator= (const vvp_arith_sum&);
 };
 
+class vvp_arith_sub  : public vvp_arith_ {
+
+    public:
+      explicit vvp_arith_sub(vvp_ipoint_t b, unsigned wid);
+
+      void set(vvp_ipoint_t i, functor_t f, bool push);
+
+    private: // not implemented
+      vvp_arith_sub(const vvp_arith_sub&);
+      vvp_arith_sub& operator= (const vvp_arith_sub&);
+};
+
 /*
  * $Log: arith.h,v $
+ * Revision 1.2  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.1  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *
diff --git a/vvp/compile.cc b/vvp/compile.cc
index 77ea6bc3b..b95d14f1e 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: compile.cc,v 1.71 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: compile.cc,v 1.72 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  "arith.h"
@@ -401,6 +401,63 @@ void compile_functor(char*label, char*type, unsigned argc, struct symb_s*argv)
       free(type);
 }
 
+static void connect_arith_inputs(vvp_ipoint_t fdx, long wid,
+				 vvp_arith_* arith,
+				 unsigned argc, struct symb_s*argv)
+{
+      unsigned opcount = argc / wid;
+
+      struct symb_s tmp_argv[4];
+      for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+	    vvp_ipoint_t ptr = ipoint_index(fdx,idx);
+	    functor_t obj = functor_index(ptr);
+
+	    obj->ival = 0xaa >> 2*(4 - opcount);
+	    obj->oval = 2;
+	    obj->odrive0 = 6;
+	    obj->odrive1 = 6;
+	    obj->mode = M42;
+	    obj->obj  = arith;
+#if defined(WITH_DEBUG)
+	    obj->breakpoint = 0;
+#endif
+
+	    for (unsigned cdx = 0 ;  cdx < opcount ;  cdx += 1)
+		  tmp_argv[cdx] = argv[idx + wid*cdx];
+
+	    inputs_connect(ptr, opcount, tmp_argv);
+      }
+
+      free(argv);
+}
+
+void compile_arith_sub(char*label, long wid, unsigned argc, struct symb_s*argv)
+{
+      assert( wid > 0 );
+
+      if ((argc % wid) != 0) {
+	    fprintf(stderr, "%s; .arith has wrong number of symbols\n", label);
+	    compile_errors += 1;
+	    free(label);
+	    return;
+      }
+
+      unsigned opcount = argc / wid;
+      if (opcount > 4) {
+	    fprintf(stderr, "%s; .arith has too many operands.\n", label);
+	    compile_errors += 1;
+	    free(label);
+	    return;
+      }
+
+      vvp_ipoint_t fdx = functor_allocate(wid);
+      define_functor_symbol(label, fdx);
+
+      vvp_arith_sub*arith = new vvp_arith_sub(fdx, wid);
+
+      connect_arith_inputs(fdx, wid, arith, argc, argv);
+}
+
 void compile_arith_sum(char*label, long wid, unsigned argc, struct symb_s*argv)
 {
       assert( wid > 0 );
@@ -425,28 +482,8 @@ void compile_arith_sum(char*label, long wid, unsigned argc, struct symb_s*argv)
 
       vvp_arith_sum*arith = new vvp_arith_sum(fdx, wid);
 
-      struct symb_s tmp_argv[4];
-      for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
-	    vvp_ipoint_t ptr = ipoint_index(fdx,idx);
-	    functor_t obj = functor_index(ptr);
+      connect_arith_inputs(fdx, wid, arith, argc, argv);
 
-	    obj->ival = 0xaa >> 2*(4 - opcount);
-	    obj->oval = 2;
-	    obj->odrive0 = 6;
-	    obj->odrive1 = 6;
-	    obj->mode = M42;
-	    obj->obj  = arith;
-#if defined(WITH_DEBUG)
-	    obj->breakpoint = 0;
-#endif
-
-	    for (unsigned cdx = 0 ;  cdx < opcount ;  cdx += 1)
-		  tmp_argv[cdx] = argv[idx + wid*cdx];
-
-	    inputs_connect(ptr, opcount, tmp_argv);
-      }
-
-      free(argv);
 }
 
 void compile_resolver(char*label, char*type, unsigned argc, struct symb_s*argv)
@@ -1262,6 +1299,9 @@ vvp_ipoint_t debug_lookup_functor(const char*name)
 
 /*
  * $Log: compile.cc,v $
+ * Revision 1.72  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.71  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *
diff --git a/vvp/compile.h b/vvp/compile.h
index a2eebdecb..4864f020a 100644
--- a/vvp/compile.h
+++ b/vvp/compile.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: compile.h,v 1.24 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: compile.h,v 1.25 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  <stdio.h>
@@ -74,6 +74,8 @@ extern void compile_resolver(char*label, char*type,
  */
 extern void compile_arith_sum(char*label, long width,
 			      unsigned argc, struct symb_s*argv);
+extern void compile_arith_sub(char*label, long width,
+			      unsigned argc, struct symb_s*argv);
 
 
 extern void compile_vpi_symbol(const char*label, vpiHandle obj);
@@ -188,6 +190,9 @@ extern void compile_net(char*label, char*name,
 
 /*
  * $Log: compile.h,v $
+ * Revision 1.25  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.24  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *
diff --git a/vvp/lexor.lex b/vvp/lexor.lex
index 16d843207..8bb1a14fd 100644
--- a/vvp/lexor.lex
+++ b/vvp/lexor.lex
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: lexor.lex,v 1.19 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: lexor.lex,v 1.20 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -65,6 +65,7 @@
 
 
   /* These are some keywords that are recognized. */
+".arith/sub" { return K_ARITH_SUB; }
 ".arith/sum" { return K_ARITH_SUM; }
 ".event"    { return K_EVENT; }
 ".event/or" { return K_EVENT_OR; }
@@ -141,6 +142,9 @@ int yywrap()
 
 /*
  * $Log: lexor.lex,v $
+ * Revision 1.20  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.19  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *
diff --git a/vvp/parse.y b/vvp/parse.y
index 853dc7aee..0e0b2030c 100644
--- a/vvp/parse.y
+++ b/vvp/parse.y
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: parse.y,v 1.28 2001/06/05 03:05:41 steve Exp $"
+#ident "$Id: parse.y,v 1.29 2001/06/07 03:09:03 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -54,7 +54,7 @@ extern FILE*yyin;
 };
 
 
-%token K_ARITH_SUM K_EVENT K_EVENT_OR K_FUNCTOR K_NET K_NET_S
+%token K_ARITH_SUB K_ARITH_SUM K_EVENT K_EVENT_OR K_FUNCTOR K_NET K_NET_S
 %token K_RESOLV K_SCOPE K_THREAD
 %token K_UDP K_UDP_C K_UDP_S
 %token K_MEM K_MEM_P K_MEM_I
@@ -156,6 +156,11 @@ statement
   /* Arithmetic statements generate functor arrays of a given width
      that take like size input vectors. */
 
+	| T_LABEL K_ARITH_SUB T_NUMBER ',' symbols ';'
+		{ struct symbv_s obj = $5;
+		  compile_arith_sub($1, $3, obj.cnt, obj.vect);
+		}
+
 	| T_LABEL K_ARITH_SUM T_NUMBER ',' symbols ';'
 		{ struct symbv_s obj = $5;
 		  compile_arith_sum($1, $3, obj.cnt, obj.vect);
@@ -453,6 +458,9 @@ int compile_design(const char*path)
 
 /*
  * $Log: parse.y,v $
+ * Revision 1.29  2001/06/07 03:09:03  steve
+ *  Implement .arith/sub subtraction.
+ *
  * Revision 1.28  2001/06/05 03:05:41  steve
  *  Add structural addition.
  *