diff --git a/vvp/Makefile.in b/vvp/Makefile.in
index 22d3b15e7..245cc0cfb 100644
--- a/vvp/Makefile.in
+++ b/vvp/Makefile.in
@@ -16,7 +16,7 @@
 #    59 Temple Place - Suite 330
 #    Boston, MA 02111-1307, USA
 #
-#ident "$Id: Makefile.in,v 1.20 2001/05/20 15:09:40 steve Exp $"
+#ident "$Id: Makefile.in,v 1.21 2001/05/31 04:12:43 steve Exp $"
 #
 #
 SHELL = /bin/sh
@@ -62,7 +62,7 @@ V = vpi_modules.o vpi_const.o vpi_iter.o vpi_mcd.o vpi_priv.o \
 vpi_scope.o vpi_signal.o vpi_tasks.o vpi_time.o vpi_memory.o \
 vpi_vthr_vector.o
 
-O = main.o parse.o parse_misc.o lexor.o compile.o debug.o functor.o \
+O = main.o parse.o parse_misc.o lexor.o bufif.o compile.o debug.o functor.o \
 resolv.o symbols.o codes.o vthread.o schedule.o tables.o udp.o memory.o $V
 
 vvp: $O
diff --git a/vvp/bufif.cc b/vvp/bufif.cc
new file mode 100644
index 000000000..9ee67ab60
--- /dev/null
+++ b/vvp/bufif.cc
@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
+ *
+ *    This source code is free software; you can redistribute it
+ *    and/or modify it in source code form under the terms of the GNU
+ *    General Public License as published by the Free Software
+ *    Foundation; either version 2 of the License, or (at your option)
+ *    any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program; if not, write to the Free Software
+ *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+#if !defined(WINNT)
+#ident "$Id: bufif.cc,v 1.1 2001/05/31 04:12:43 steve Exp $"
+#endif
+
+# include  "bufif.h"
+# include  "functor.h"
+# include  "schedule.h"
+
+void vvp_bufif0_s::set(vvp_ipoint_t ptr, functor_t fp, bool push)
+{
+      unsigned in0 = fp->ival & 0x03;
+      unsigned in1 = (fp->ival >> 2) & 0x03;
+
+      unsigned char out0 = 0x00 | (fp->odrive0<<0) | (fp->odrive0<<4);
+      unsigned char out1 = 0x88 | (fp->odrive1<<0) | (fp->odrive1<<4);
+      unsigned char outX = 0x80 | (fp->odrive1<<0) | (fp->odrive0<<4);
+      unsigned char outH = 0x88 | (fp->odrive1<<4) | (0);
+      unsigned char outL = 0x00 | (fp->odrive1<<0) | (0);
+
+      switch (in1) {
+
+	  case 0:
+	    switch (in0) {
+		case 0:
+		  fp->oval = 0;
+		  fp->ostr = out0;
+		  break;
+		case 1:
+		  fp->oval = 1;
+		  fp->ostr = out1;
+		  break;
+		default:
+		  fp->oval = 2;
+		  fp->ostr = outX;
+		  break;
+	    }
+	    break;
+
+	  case 1:
+	    fp->oval = 3;
+	    fp->ostr = HiZ;
+	    break;
+
+	  default:
+	    fp->oval = 2;
+	    switch (in0) {
+		case 0:
+		  fp->ostr = outL;
+		  break;
+		case 1:
+		  fp->ostr = outH;
+		  break;
+		default:
+		  fp->ostr = outX;
+		  break;
+	    }
+	    break;
+      }
+
+      if (push)
+	    functor_propagate(ptr);
+      else
+	    schedule_functor(ptr, 0);
+}
+
+void vvp_bufif1_s::set(vvp_ipoint_t ptr, functor_t fp, bool push)
+{
+      unsigned in0 = fp->ival & 0x03;
+      unsigned in1 = (fp->ival >> 2) & 0x03;
+
+      unsigned char out0 = 0x00 | (fp->odrive0<<0) | (fp->odrive0<<4);
+      unsigned char out1 = 0x88 | (fp->odrive1<<0) | (fp->odrive1<<4);
+      unsigned char outX = 0x80 | (fp->odrive1<<0) | (fp->odrive0<<4);
+      unsigned char outH = 0x88 | (fp->odrive1<<4) | (0);
+      unsigned char outL = 0x00 | (fp->odrive1<<0) | (0);
+
+      switch (in1) {
+
+	  case 1:
+	    switch (in0) {
+		case 0:
+		  fp->oval = 0;
+		  fp->ostr = out0;
+		  break;
+		case 1:
+		  fp->oval = 1;
+		  fp->ostr = out1;
+		  break;
+		default:
+		  fp->oval = 2;
+		  fp->ostr = outX;
+		  break;
+	    }
+	    break;
+
+	  case 0:
+	    fp->oval = 3;
+	    fp->ostr = HiZ;
+	    break;
+
+	  default:
+	    fp->oval = 2;
+	    switch (in0) {
+		case 0:
+		  fp->ostr = outL;
+		  break;
+		case 1:
+		  fp->ostr = outH;
+		  break;
+		default:
+		  fp->ostr = outX;
+		  break;
+	    }
+	    break;
+      }
+
+      if (push)
+	    functor_propagate(ptr);
+      else
+	    schedule_functor(ptr, 0);
+}
+
+/*
+ * $Log: bufif.cc,v $
+ * Revision 1.1  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
+ */
+
diff --git a/vvp/bufif.h b/vvp/bufif.h
new file mode 100644
index 000000000..68e6f6b49
--- /dev/null
+++ b/vvp/bufif.h
@@ -0,0 +1,50 @@
+#ifndef __bufif_H
+#define __bufif_H
+/*
+ * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
+ *
+ *    This source code is free software; you can redistribute it
+ *    and/or modify it in source code form under the terms of the GNU
+ *    General Public License as published by the Free Software
+ *    Foundation; either version 2 of the License, or (at your option)
+ *    any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program; if not, write to the Free Software
+ *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+#if !defined(WINNT)
+#ident "$Id: bufif.h,v 1.1 2001/05/31 04:12:43 steve Exp $"
+#endif
+
+# include  "functor.h"
+
+class vvp_bufif0_s  : public vvp_fobj_s {
+
+    public:
+      virtual void set(vvp_ipoint_t i, functor_t f, bool push);
+
+    private: // not implemented
+};
+
+class vvp_bufif1_s  : public vvp_fobj_s {
+
+    public:
+      virtual void set(vvp_ipoint_t i, functor_t f, bool push);
+
+    private: // not implemented
+};
+
+/*
+ * $Log: bufif.h,v $
+ * Revision 1.1  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
+ */
+#endif
diff --git a/vvp/compile.cc b/vvp/compile.cc
index 7a8c8364c..21f0bb8d6 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -17,9 +17,10 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: compile.cc,v 1.69 2001/05/30 03:02:35 steve Exp $"
+#ident "$Id: compile.cc,v 1.70 2001/05/31 04:12:43 steve Exp $"
 #endif
 
+# include  "bufif.h"
 # include  "compile.h"
 # include  "functor.h"
 # include  "resolv.h"
@@ -355,10 +356,12 @@ void compile_functor(char*label, char*type, unsigned argc, struct symb_s*argv)
 	    obj->table = ft_BUF;
 
       } else if (strcmp(type, "BUFIF0") == 0) {
-	    obj->table = ft_BUFIF0;
+	    obj->obj = new vvp_bufif0_s;
+	    obj->mode = M42;
 
       } else if (strcmp(type, "BUFIF1") == 0) {
-	    obj->table = ft_BUFIF1;
+	    obj->obj = new vvp_bufif1_s;
+	    obj->mode = M42;
 
       } else if (strcmp(type, "MUXZ") == 0) {
 	    obj->table = ft_MUXZ;
@@ -1207,6 +1210,10 @@ vvp_ipoint_t debug_lookup_functor(const char*name)
 
 /*
  * $Log: compile.cc,v $
+ * Revision 1.70  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.69  2001/05/30 03:02:35  steve
  *  Propagate strength-values instead of drive strengths.
  *
diff --git a/vvp/debug.cc b/vvp/debug.cc
index f265aa33c..ef9a234db 100644
--- a/vvp/debug.cc
+++ b/vvp/debug.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: debug.cc,v 1.3 2001/05/30 03:02:35 steve Exp $"
+#ident "$Id: debug.cc,v 1.4 2001/05/31 04:12:43 steve Exp $"
 #endif
 
 /*
@@ -97,7 +97,7 @@ static void cmd_functor(unsigned argc, char*argv[])
 		   bitval_tab[(fp->ival>>4)&3], fp->istr[2],
 		   bitval_tab[(fp->ival>>6)&3], fp->istr[3]);
 	    printf("out value    = %c (%02x)\n",
-		   bitval_tab[fp->oval], 0 /*xxxx*/);
+		   bitval_tab[fp->oval], fp->ostr);
       }
 }
 
@@ -167,6 +167,10 @@ void breakpoint(void)
 #endif
 /*
  * $Log: debug.cc,v $
+ * Revision 1.4  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.3  2001/05/30 03:02:35  steve
  *  Propagate strength-values instead of drive strengths.
  *
diff --git a/vvp/functor.cc b/vvp/functor.cc
index 699609c94..b15ae0802 100644
--- a/vvp/functor.cc
+++ b/vvp/functor.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: functor.cc,v 1.21 2001/05/30 03:02:35 steve Exp $"
+#ident "$Id: functor.cc,v 1.22 2001/05/31 04:12:43 steve Exp $"
 #endif
 
 # include  "functor.h"
@@ -155,6 +155,22 @@ static void functor_set_mode0(vvp_ipoint_t ptr, functor_t fp, bool push)
 	/* If the output changes, then create a propagation event. */
       if (out != fp->oval) {
 	    fp->oval = out;
+
+	    switch (out) {
+		case 0:
+		  fp->ostr = 0x00 | (fp->odrive0<<0) | (fp->odrive0<<4);
+		  break;
+		case 1:
+		  fp->ostr = 0x88 | (fp->odrive1<<0) | (fp->odrive1<<4);
+		  break;
+		case 2:
+		  fp->ostr = 0x80 | (fp->odrive0<<0) | (fp->odrive1<<4);
+		  break;
+		case 3:
+		  fp->ostr = 0x00;
+		  break;
+	    }
+
 	    if (push)
 		  functor_propagate(ptr);
 	    else
@@ -305,31 +321,14 @@ void functor_propagate(vvp_ipoint_t ptr)
 {
       functor_t fp = functor_index(ptr);
       unsigned char oval = fp->oval;
-      unsigned drive0 = fp->odrive0;
-      unsigned drive1 = fp->odrive1;
-
-      unsigned str;
-      switch (oval) {
-	  case 0:
-	    str = 0x00 | (drive0<<0) | (drive0<<4);
-	    break;
-	  case 1:
-	    str = 0x88 | (drive1<<0) | (drive1<<4);
-	    break;
-	  case 2:
-	    str = 0x80 | (drive0<<0) | (drive1<<4);
-	    break;
-	  case 3:
-	    str = 0x00;
-	    break;
-      }
+      unsigned char ostr = fp->ostr;
 
       vvp_ipoint_t idx = fp->out;
       while (idx) {
 	    functor_t idxp = functor_index(idx);
 	    vvp_ipoint_t next = idxp->port[ipoint_port(idx)];
 
-	    functor_set(idx, oval, str, false);
+	    functor_set(idx, oval, ostr, false);
 	    idx = next;
       }
 }
@@ -360,6 +359,10 @@ const unsigned char ft_var[16] = {
 
 /*
  * $Log: functor.cc,v $
+ * Revision 1.22  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.21  2001/05/30 03:02:35  steve
  *  Propagate strength-values instead of drive strengths.
  *
diff --git a/vvp/functor.h b/vvp/functor.h
index 4b5b574c8..2cdec0019 100644
--- a/vvp/functor.h
+++ b/vvp/functor.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: functor.h,v 1.23 2001/05/30 03:02:35 steve Exp $"
+#ident "$Id: functor.h,v 1.24 2001/05/31 04:12:43 steve Exp $"
 #endif
 
 # include  "pointers.h"
@@ -100,6 +100,9 @@
  *    STRONG = 6,
  *    SUPPLY = 7
  *
+ * The output value (oval) is combined with the drive specifications
+ * to make a fully strength aware output, as described below.
+ *
  * OUTPUT STRENGTHS:
  *
  * The strength-aware outputs are specified as an 8 bit value, that is
@@ -108,6 +111,11 @@
  * strength and one bit of value, like so: VSSS. The high nible has
  * the strength-value closest to supply1, and the low nibble has the
  * strength-value closest to supply0.
+ *
+ * The functor calculates, when it operates, a 4-value output into
+ * oval and a fully strength aware value into ostr. The mode-0
+ * functors use the odrive0 and odrive1 fields to form the strength
+ * value.
  */
 
 struct functor_s {
@@ -130,13 +138,16 @@ struct functor_s {
       unsigned oval       : 2;
       unsigned odrive0    : 3;
       unsigned odrive1    : 3;
+	/* Strength form of the output value. */
+      unsigned ostr       : 8;
+
 #if defined(WITH_DEBUG)
 	/* True if this functor triggers a breakpoint. */
       unsigned breakpoint : 1;
 #endif
 
 	/* functor mode:  0 == table ;  1 == event ; 2 == named event */
-      unsigned char mode;
+      unsigned mode       : 2;
       union {
  	    unsigned char old_ival; // mode 3
       };
@@ -173,7 +184,7 @@ enum strength_e {
  * it happens when it happens.
  */
 
-#define M42 42
+#define M42 3
 
 struct vvp_fobj_s {
       virtual unsigned get(vvp_ipoint_t i, functor_t f);
@@ -282,6 +293,10 @@ extern const unsigned char ft_var[];
 
 /*
  * $Log: functor.h,v $
+ * Revision 1.24  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.23  2001/05/30 03:02:35  steve
  *  Propagate strength-values instead of drive strengths.
  *
diff --git a/vvp/resolv.cc b/vvp/resolv.cc
index b37524db6..8c6ca2e54 100644
--- a/vvp/resolv.cc
+++ b/vvp/resolv.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: resolv.cc,v 1.3 2001/05/30 03:02:35 steve Exp $"
+#ident "$Id: resolv.cc,v 1.4 2001/05/31 04:12:43 steve Exp $"
 #endif
 
 # include  "resolv.h"
@@ -118,9 +118,9 @@ static unsigned blend(unsigned a, unsigned b)
 }
 
 /*
- * For now, cheat and resolve the values without using the actual
- * strengths. The strengths are not yet available to the inputs, so
- * this is all we can do for now.
+ * Resolve the strength values of the inputs, two at a time. Pairs of
+ * inputs are resolved with the blend function, and the final value is
+ * reduced to a 4-value result for propagation.
  */
 void vvp_resolv_s::set(vvp_ipoint_t ptr, functor_t fp, bool push)
 {
@@ -146,6 +146,8 @@ void vvp_resolv_s::set(vvp_ipoint_t ptr, functor_t fp, bool push)
 	    break;
       }
 
+      fp->ostr = val;
+
 	/* If the output changes, then create a propagation event. */
       if (oval != fp->oval) {
 	    fp->oval = oval;
@@ -158,6 +160,10 @@ void vvp_resolv_s::set(vvp_ipoint_t ptr, functor_t fp, bool push)
 
 /*
  * $Log: resolv.cc,v $
+ * Revision 1.4  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.3  2001/05/30 03:02:35  steve
  *  Propagate strength-values instead of drive strengths.
  *
diff --git a/vvp/udp.cc b/vvp/udp.cc
index 23dac5a51..85c12129b 100644
--- a/vvp/udp.cc
+++ b/vvp/udp.cc
@@ -18,7 +18,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: udp.cc,v 1.4 2001/05/06 03:51:37 steve Exp $"
+#ident "$Id: udp.cc,v 1.5 2001/05/31 04:12:43 steve Exp $"
 #endif
 
 #include "udp.h"
@@ -33,6 +33,21 @@ void vvp_udp_s::set(vvp_ipoint_t ptr, functor_t fp, bool)
 {
   unsigned char out = propagate_(ptr);
 
+  switch (out) {
+      case 0:
+	fp->ostr = 0x00 | (fp->odrive0<<0) | (fp->odrive0<<4);
+	break;
+      case 1:
+	fp->ostr = 0x88 | (fp->odrive1<<0) | (fp->odrive1<<4);
+	break;
+      case 2:
+	fp->ostr = 0x80 | (fp->odrive0<<0) | (fp->odrive1<<4);
+	break;
+      case 3:
+	fp->ostr = 0x00;
+	break;
+  }
+
   if (out != fp->oval) 
     {
       fp->oval = out;
@@ -208,6 +223,10 @@ unsigned char vvp_udp_s::propagate_(vvp_ipoint_t uix)
 
 /*
  * $Log: udp.cc,v $
+ * Revision 1.5  2001/05/31 04:12:43  steve
+ *  Make the bufif0 and bufif1 gates strength aware,
+ *  and accurately propagate strengths of outputs.
+ *
  * Revision 1.4  2001/05/06 03:51:37  steve
  *  Regularize the mode-42 functor handling.
  *