diff --git a/C/absmi.c b/C/absmi.c
index f456259dc..af61d16bf 100644
--- a/C/absmi.c
+++ b/C/absmi.c
@@ -290,7 +290,7 @@ Yap_absmi(int inp)
 #if PUSH_REGS
       restore_absmi_regs(old_regs);
 #endif
-      if (!Yap_growheap(FALSE)) {
+      if (!Yap_growheap(FALSE, 0)) {
 	saveregs();
 	Yap_Error(SYSTEM_ERROR, TermNil, "YAP failed to grow heap: %s", Yap_ErrorMessage);
 	setregs();
@@ -10208,7 +10208,7 @@ Yap_absmi(int inp)
 #ifdef LOW_LEVEL_TRACER
       if (Yap_do_low_level_trace) {
 	RESET_VARIABLE(H);
-	H[1] = PREG->u.ycx.c;
+	H[1] = XREG(PREG->u.ycx.c);
 	H[2] = XREG(PREG->u.ycx.xi);
 	low_level_trace(enter_pred,RepPredProp(Yap_GetPredPropByFunc(Yap_MkFunctor(Yap_LookupAtom("functor"),3),0)),H);
       }
diff --git a/C/amasm.c b/C/amasm.c
index 139bcfe99..f3e362a2e 100644
--- a/C/amasm.c
+++ b/C/amasm.c
@@ -2337,8 +2337,9 @@ do_pass(void)
       }
       if (!pass_no) {
 	if (CellPtr(label_offset+cpc->rnd1) > ASP-256) {
+	  Yap_Error_Size = 256+((char *)(label_offset+cpc->rnd1) - (char *)H);
 	  save_machine_regs();
-	  longjmp(Yap_CompilerBotch,3);	  
+	  longjmp(Yap_CompilerBotch, 3);	  
 	}
 	
 	if ( (char *)(label_offset+cpc->rnd1) > freep)
@@ -2537,7 +2538,7 @@ Yap_assemble(int mode)
       size = (CELL)code_p;
   }
   while ((code_addr = (yamop *) Yap_AllocCodeSpace(size)) == NULL) {
-    if (!Yap_growheap(TRUE)) {
+    if (!Yap_growheap(TRUE, size)) {
       Yap_Error_TYPE = SYSTEM_ERROR;
       return NULL;
     }
diff --git a/C/arrays.c b/C/arrays.c
index 27dc6d3e2..a5c9018a4 100644
--- a/C/arrays.c
+++ b/C/arrays.c
@@ -441,7 +441,7 @@ AllocateStaticArraySpace(StaticArrayEntry *p, static_array_types atype, Int arra
   }
   while ((p->ValueOfVE.floats = (Float *) Yap_AllocAtomSpace(asize) ) == NULL) {
     YAPLeaveCriticalSection();
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, asize)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return;
     }
@@ -455,7 +455,7 @@ CreateStaticArray(AtomEntry *ae, Int dim, static_array_types type, CODEADDR star
 {
   if (EndOfPAEntr(p)) {
     while ((p = (StaticArrayEntry *) Yap_AllocAtomSpace(sizeof(*p))) == NULL) {
-      if (!Yap_growheap(FALSE)) {
+      if (!Yap_growheap(FALSE, sizeof(*p))) {
 	Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	return NULL;
       }
diff --git a/C/c_interface.c b/C/c_interface.c
index 3a180f5ec..390ede766 100644
--- a/C/c_interface.c
+++ b/C/c_interface.c
@@ -591,7 +591,7 @@ YAP_AllocSpaceFromYap(unsigned int size)
   BACKUP_MACHINE_REGS();
 
   if ((ptr = Yap_AllocCodeSpace(size)) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(NULL);
     }
diff --git a/C/cdmgr.c b/C/cdmgr.c
index 954ce3513..fe6dfd1f1 100644
--- a/C/cdmgr.c
+++ b/C/cdmgr.c
@@ -763,7 +763,7 @@ static void  expand_consult(void)
   ConsultCapacity += InitialConsultCapacity;
   /* I assume it always works ;-) */
   while ((new_cl = (consult_obj *)Yap_AllocCodeSpace(sizeof(consult_obj)*ConsultCapacity)) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, sizeof(consult_obj)*ConsultCapacity)) {
       Yap_Error(SYSTEM_ERROR,TermNil,Yap_ErrorMessage);
       return;
     }
diff --git a/C/compiler.c b/C/compiler.c
index 38cd1b033..2ba11cdf2 100644
--- a/C/compiler.c
+++ b/C/compiler.c
@@ -136,8 +136,9 @@ pop_code(unsigned int level)
     return;
   if (cpc->op == pop_op)
     ++(cpc->rnd1);
-  else
+  else {
     Yap_emit(pop_op, One, Zero);
+  }
 }
 
 static void
@@ -462,7 +463,7 @@ c_arg(Int argno, Term t, unsigned int arity, unsigned int level)
 	dest[2] = src[2];
 #endif
 	/* note that we don't need to copy size info, unless we wanted
-	 to garbage collect clauses ;-) */
+	   to garbage collect clauses ;-) */
 	icpc = cpc;
 	if (BlobsStart == NULL)
 	  BlobsStart = CodeStart;
@@ -556,8 +557,9 @@ c_arg(Int argno, Term t, unsigned int arity, unsigned int level)
     }
     c_arg(2, TailOfTerm(t), 2, level);
     --level;
-    if (argno != (Int)arity)
+    if (argno != (Int)arity) {
       pop_code(level);
+    }
   } else if (IsRefTerm(t)) {
     READ_LOCK(CurrentPred->PRWLock);
     if (!(CurrentPred->PredFlags & (DynamicPredFlag|LogUpdatePredFlag))) {
@@ -595,8 +597,9 @@ c_arg(Int argno, Term t, unsigned int arity, unsigned int level)
     ++level;
     c_args(t, level);
     --level;
-    if (argno != (Int)arity)
+    if (argno != (Int)arity) {
       pop_code(level);
+    }
   }
 }
 
@@ -2682,6 +2685,7 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
 
   /* first, initialise Yap_CompilerBotch to handle all cases of interruptions */
   Yap_ErrorMessage = NULL;
+  Yap_Error_Size = 0;
   if ((botch_why = setjmp(Yap_CompilerBotch)) == 3) {
     /* out of local stack, just duplicate the stack */
     restore_machine_regs();
@@ -2689,7 +2693,7 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
     {
       Int osize = 2*sizeof(CELL)*(ASP-H);
       ARG1 = my_clause;
-      if (!Yap_gc(2, ENV, P)) {
+      if (!Yap_gcl(Yap_Error_Size, 2, ENV, P)) {
 	Yap_Error_TYPE = OUT_OF_STACK_ERROR;
 	Yap_Error_Term = my_clause;
       }
@@ -2723,7 +2727,7 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
     reset_vars();
     return (0);
   }
-  SaveH = H;
+  HB = H;
   or_found = 0;
   Yap_ErrorMessage = NULL;
   /* initialize variables for code generation                              */
@@ -2731,7 +2735,8 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
   BlobsStart = icpc = NULL;
   freep = freep0 = (char *) (H + maxvnum);
   if (ASP <= CellPtr (freep) + 256) {
-    vtable = NIL;
+    vtable = NULL;
+    Yap_Error_Size = (256+maxvnum)*sizeof(CELL);
     save_machine_regs();
     longjmp(Yap_CompilerBotch,3);
   }
@@ -2746,7 +2751,7 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
    * 2000 added to H in case we need to construct call(G) when G is a
    * variable used as a goal                                       
    */
-  vtable = NIL;
+  vtable = NULL;
   labelno = 0L;
 
   if (IsVarTerm(my_clause)) {
@@ -2802,7 +2807,8 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
     BlobsStart = NULL;
   }
   reset_vars();
-  H = SaveH;
+  H = HB;
+  HB = B->cp_h;
   if (Yap_ErrorMessage)
     return (0);
 #ifdef DEBUG
@@ -2859,7 +2865,7 @@ Yap_cclause(Term inp_clause, int NOfArgs, int mod)
   if (acode == NIL) {
     /* make sure we have enough space */
     reset_vars();
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       save_machine_regs();
       my_clause = Deref(ARG1);
       longjmp(Yap_CompilerBotch, 2);
diff --git a/C/computils.c b/C/computils.c
index 02cd03996..5d426c767 100644
--- a/C/computils.c
+++ b/C/computils.c
@@ -65,6 +65,7 @@ AllocCMem (int size)
 #endif
   freep += size;
   if (ASP <= CellPtr (freep) + 256) {
+    Yap_Error_Size = 256+((char *)freep - (char *)H);
     save_machine_regs();
     longjmp(Yap_CompilerBotch,3);
   }
@@ -82,24 +83,21 @@ Yap_is_a_test_pred (Term arg, SMALLUNSGN mod)
 {
   if (IsVarTerm (arg))
     return (FALSE);
-  else if (IsAtomTerm (arg))
-    {
+  else if (IsAtomTerm (arg)) {
       Atom At = AtomOfTerm (arg);
       PredEntry *pe = RepPredProp(PredPropByAtom(At, mod));
       if (EndOfPAEntr(pe))
 	return (FALSE);
       return (pe->PredFlags & TestPredFlag);
-    }
-  else if (IsApplTerm (arg))
-    {
-      Functor f = FunctorOfTerm (arg);
+  } else if (IsApplTerm (arg)) {
+    Functor f = FunctorOfTerm (arg);
       PredEntry *pe = RepPredProp(PredPropByFunc(f, mod));
       if (EndOfPAEntr(pe))
 	return (FALSE);
       return (pe->PredFlags & TestPredFlag);
-    }
-  else
+  } else {
     return (FALSE);
+  }
 }
 
 void
@@ -110,14 +108,13 @@ Yap_emit (compiler_vm_op o, Int r1, CELL r2)
   p->op = o;
   p->rnd1 = r1;
   p->rnd2 = r2;
-  p->nextInst = NIL;
-  if (cpc == NIL)
+  p->nextInst = NULL;
+  if (cpc == NIL) {
     cpc = CodeStart = p;
-  else
-    {
-      cpc->nextInst = p;
-      cpc = p;
-    }
+  } else {
+    cpc->nextInst = p;
+    cpc = p;
+  }
 }
 
 void
diff --git a/C/dbase.c b/C/dbase.c
index b4ccfdf4b..7c48bb089 100644
--- a/C/dbase.c
+++ b/C/dbase.c
@@ -940,6 +940,7 @@ static CELL *MkDBTerm(register CELL *pt0, register CELL *pt0_end,
   return(CodeMax);
 
  error:
+  Yap_Error_Size = 1024+((char *)AuxSp-(char *)HeapTop);
   DBErrorFlag = OVF_ERROR_IN_DB;
   *vars_foundp = vars_found;
 #ifdef RATIONAL_TREES
@@ -1391,6 +1392,7 @@ CreateDBStruct(Term Tm, DBProp p, int InFlag)
       CodeAbs++;	/* We have one more cell */
       CodeAbs += CellPtr(lr) - CellPtr(LinkAr);
       if ((CELL *)((char *)ntp0+(CELL)CodeAbs) > AuxSp) {
+	Yap_Error_Size = (UInt)DBLength(CodeAbs);
 	DBErrorFlag = OVF_ERROR_IN_DB;
 	Yap_ReleasePreAllocCodeSpace((ADDR)pp0);
 	return(NULL);
@@ -1417,6 +1419,7 @@ CreateDBStruct(Term Tm, DBProp p, int InFlag)
     if (tofref != TmpRefBase) {
       CodeAbs += TmpRefBase - tofref + 1;
       if ((CELL *)((char *)ntp0+(CELL)CodeAbs) > AuxSp) {
+	Yap_Error_Size = (UInt)DBLength(CodeAbs);
 	DBErrorFlag = OVF_ERROR_IN_DB;
 	Yap_ReleasePreAllocCodeSpace((ADDR)pp0);
 	return(NULL);
@@ -1437,6 +1440,7 @@ CreateDBStruct(Term Tm, DBProp p, int InFlag)
 #endif
     pp = AllocDBSpace(DBLength(CodeAbs));
     if (pp == NIL) {
+      Yap_Error_Size = (UInt)DBLength(CodeAbs);
       DBErrorFlag = OVF_ERROR_IN_DB;
       DBErrorNumber = SYSTEM_ERROR;
       DBErrorTerm = TermNil;
@@ -1735,6 +1739,7 @@ p_rcda(void)
   if (!IsVarTerm(Deref(ARG3)))
     return (FALSE);
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkFirst, t1, t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1749,7 +1754,7 @@ p_rcda(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -1774,6 +1779,7 @@ p_rcdap(void)
   if (!IsVarTerm(Deref(ARG3)))
     return FALSE;
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkFirst | MkCode, t1, t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1788,7 +1794,7 @@ p_rcdap(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return FALSE;
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return FALSE;
     } else {
@@ -1823,6 +1829,7 @@ p_rcda_at(void)
       return(FALSE);
   }
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record_at(MkFirst, DBRefOfTerm(t1), t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1837,7 +1844,7 @@ p_rcda_at(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -1862,6 +1869,7 @@ p_rcdz(void)
   if (!IsVarTerm(Deref(ARG3)))
     return (FALSE);
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkLast, t1, t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1876,7 +1884,7 @@ p_rcdz(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -1901,6 +1909,7 @@ p_rcdzp(void)
   if (!IsVarTerm(Deref(ARG3)))
     return (FALSE);
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkLast | MkCode, t1, t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1915,7 +1924,7 @@ p_rcdzp(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -1949,6 +1958,7 @@ p_rcdz_at(void)
       return(FALSE);
   }
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record_at(MkLast, DBRefOfTerm(t1), t2, Unsigned(0)));
   switch(DBErrorFlag) {
   case NO_ERROR_IN_DB:
@@ -1963,7 +1973,7 @@ p_rcdz_at(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recordz_at/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -1993,6 +2003,7 @@ p_rcdstatp(void)
     return (FALSE);
   mk_first = ((IntOfTerm(t3) % 4) == 2);
  restart_record:
+  Yap_Error_Size = 0;
   if (mk_first)
     TRef = MkDBRefTerm(record(MkFirst | MkCode, t1, t2, MkIntTerm(0)));
   else
@@ -2010,7 +2021,7 @@ p_rcdstatp(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in record_stat_source/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -2037,6 +2048,7 @@ p_drcdap(void)
   if (IsVarTerm(t4) || !IsIntegerTerm(t4))
     return (FALSE);
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkFirst | MkCode | WithRef,
 			    t1, t2, t4));
   switch(DBErrorFlag) {
@@ -2052,7 +2064,7 @@ p_drcdap(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -2080,6 +2092,7 @@ p_drcdzp(void)
   if (IsVarTerm(t4) || !IsIntegerTerm(t4))
     return (FALSE);
  restart_record:
+  Yap_Error_Size = 0;
   TRef = MkDBRefTerm(record(MkLast | MkCode | WithRef,
 			    t1, t2, t4));
   switch(DBErrorFlag) {
@@ -2095,7 +2108,7 @@ p_drcdzp(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -2120,6 +2133,7 @@ p_rcdaifnot(void)
   DBRef           db_ref;
 
  restart_record:
+  Yap_Error_Size = 0;
   if (!IsVarTerm(Deref(ARG3)))
     return (FALSE);
   found_one = NIL;
@@ -2140,7 +2154,7 @@ p_rcdaifnot(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -2162,6 +2176,7 @@ p_rcdzifnot(void)
   DBRef           db_ref;
 
  restart_record:
+  Yap_Error_Size = 0;
   if (!IsVarTerm(Deref(ARG3)))
     return (FALSE);
   found_one = NIL;
@@ -2182,7 +2197,7 @@ p_rcdzifnot(void)
     Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
     return(FALSE);
   case OVF_ERROR_IN_DB:
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     } else
@@ -2544,7 +2559,7 @@ nth_recorded_log(LogUpdDBProp AtProp, Int Count)
   } else {
     if (AtProp->Index == NULL) {
       while((AtProp->Index = new_lu_index(AtProp)) == NULL) {
-	if (!Yap_growheap(FALSE)) {
+	if (!Yap_growheap(FALSE,DBLength((AtProp->NOfEntries+1)*sizeof(DBRef *)))) {
 	  Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	  READ_UNLOCK(AtProp->DBRWLock);
 	  return NULL;
@@ -2732,7 +2747,7 @@ i_log_upd_recorded(LogUpdDBProp AtProp)
   } else {
     if (AtProp->Index == NULL) {
       while((AtProp->Index = new_lu_index(AtProp)) == NULL) {
-	if (!Yap_growheap(FALSE)) {
+	if (!Yap_growheap(FALSE,DBLength((AtProp->NOfEntries+1)*sizeof(DBRef *)))) {
 	  Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	  return FALSE;
 	}
@@ -4262,6 +4277,7 @@ StoreTermInDB(int arg, int nargs)
 {
   DBRef x;
   Term t = Deref(XREGS[arg]);
+  Yap_Error_Size = 0;
 
   while ((x = CreateDBStruct(t, (DBProp)NIL,
 			  InQueue)) == NULL) {
@@ -4283,7 +4299,7 @@ StoreTermInDB(int arg, int nargs)
       Yap_Error(SYSTEM_ERROR, TermNil, "YAP could not grow trail in recorda/3");
       return(FALSE);
     case OVF_ERROR_IN_DB:
-      if (!Yap_growheap(FALSE)) {
+      if (!Yap_growheap(FALSE, Yap_Error_Size)) {
 	Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	return(FALSE);
       } else {
@@ -4311,7 +4327,7 @@ p_init_queue(void)
   Term t;
 
   while ((dbq = (db_queue *)AllocDBSpace(sizeof(db_queue))) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, sizeof(db_queue))) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     }
diff --git a/C/grow.c b/C/grow.c
index 82d818fc6..385c45401 100644
--- a/C/grow.c
+++ b/C/grow.c
@@ -644,12 +644,15 @@ fix_tabling_info(void)
 #endif /* TABLING */
 
 int
-Yap_growheap(int fix_code)
+Yap_growheap(int fix_code, UInt in_size)
 {
   unsigned long size = sizeof(CELL) * 16 * 1024L;
   int shift_factor = (heap_overflows > 8 ? 8 : heap_overflows);
   unsigned long sz =  size << shift_factor;
 
+  if (sz < in_size) {
+    sz = in_size;
+  }
 #if defined(YAPOR) || defined(THREADS)
   if (NOfThreads != 1) {
     Yap_Error(SYSTEM_ERROR,TermNil,"cannot grow Heap: more than a worker/thread running");
@@ -661,6 +664,9 @@ Yap_growheap(int fix_code)
   while(sz >= sizeof(CELL) * 16 * 1024L && !static_growheap(sz, fix_code)) {
     size = size/2;
     sz =  size << shift_factor;
+    if (sz < in_size) {
+      return FALSE;
+    }
   }
   /* we must fix an instruction chain */
   if (fix_code) {
diff --git a/C/heapgc.c b/C/heapgc.c
index 4b9709e4e..df113d342 100644
--- a/C/heapgc.c
+++ b/C/heapgc.c
@@ -3050,7 +3050,7 @@ do_gc(Int predarity, CELL *current_env, yamop *nextop)
   }
   if (HeapTop >= Yap_GlobalBase - MinHeapGap) {
     *--ASP = (CELL)current_env;
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, MinHeapGap)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     }
@@ -3155,13 +3155,13 @@ p_inform_gc(void)
 }
 
 
-int 
-Yap_gc(Int predarity, CELL *current_env, yamop *nextop)
+static int
+call_gc(UInt gc_lim, Int predarity, CELL *current_env, yamop *nextop)
 {
-  Int           gc_margin = 128;
-  Term          Tgc_margin;
-  Int           effectiveness = 0;
-  int           gc_on = FALSE;
+  UInt   gc_margin = 128;
+  Term   Tgc_margin;
+  Int    effectiveness = 0;
+  int    gc_on = FALSE;
 
 #if defined(YAPOR) || defined(THREADS)
   if (NOfThreads != 1) {
@@ -3171,39 +3171,34 @@ Yap_gc(Int predarity, CELL *current_env, yamop *nextop)
 #endif
   if (Yap_GetValue(AtomGc) != TermNil)
     gc_on = TRUE;
-  if (IsIntTerm(Tgc_margin = Yap_GetValue(AtomGcMargin))) {
-    gc_margin = IntOfTerm(Tgc_margin);
+  if (IsIntegerTerm(Tgc_margin = Yap_GetValue(AtomGcMargin)) &&
+      gc_margin > 0) {
+    gc_margin = (UInt)IntegerOfTerm(Tgc_margin);
   } else {
+    /* only go exponential for the first 8 calls */
     if (gc_calls < 8) 
       gc_margin <<= gc_calls;
-    else
+    else {
+      /* next grow linearly */
       gc_margin <<= 8;
+      gc_margin *= gc_calls;
+    }
   }
-  if (gc_margin < 0 || gc_margin > 4000) {
-    gc_margin = (LCL0 - H0) >> 9;
-  }
-  gc_margin = gc_margin << 8;
+  if (gc_margin < gc_lim)
+    gc_margin = gc_lim;
   if (gc_on) {
     effectiveness = do_gc(predarity, current_env, nextop);
-  }
-  if (effectiveness > 90) {
-    while (gc_margin < H-H0) 
-      gc_margin <<= 1;
+    if (effectiveness > 90) {
+      while (gc_margin < H-H0) 
+	gc_margin <<= 1;
+    }
+  } else {
+    effectiveness = 0;
   }
   /* expand the stack if effectiveness is less than 20 % */
-  if (ASP - H < gc_margin || !gc_on || effectiveness < 20) {
-    Int gap = CalculateStackGap();
-    if (ASP-H > gc_margin)
-      gc_margin = (ASP-H)+gap;
-    else
-      gc_margin = 8 * (gc_margin - (ASP - H));
-    gc_margin = ((gc_margin >> 16) + 1) << 16;
-    if (gc_margin < gap)
-      gc_margin = gap;
-    while (gc_margin >= gap && !Yap_growstack(gc_margin))
-      gc_margin = gc_margin/2;
-    check_global();
-    return(gc_margin >= gap);
+  if (ASP - H < gc_margin ||
+      effectiveness < 20) {
+    return (Yap_growstack(gc_margin));
   }
   /*
    * debug for(save_total=1; save_total<=N; ++save_total)
@@ -3212,6 +3207,18 @@ Yap_gc(Int predarity, CELL *current_env, yamop *nextop)
   return ( TRUE );
 }
 
+int 
+Yap_gc(Int predarity, CELL *current_env, yamop *nextop)
+{
+  return call_gc(128, predarity, current_env, nextop);
+}
+
+int 
+Yap_gcl(UInt gc_lim, Int predarity, CELL *current_env, yamop *nextop)
+{
+  return call_gc(gc_lim, predarity, current_env, nextop);
+}
+
 
 static Int
 p_gc(void)
diff --git a/C/index.c b/C/index.c
index 1ffe60d7c..16bab7a07 100644
--- a/C/index.c
+++ b/C/index.c
@@ -1031,6 +1031,7 @@ add_info(ClauseDef *clause, UInt regno)
     case _get_x_var:
       if (regcopy_in(myregs, nofregs, cl->u.xx.xr)) {
 	nofregs = add_regcopy(myregs, nofregs, cl->u.xx.xl);
+	cl = NEXTOP(cl,xx);
 	break;
       }
     case _put_x_var:
@@ -2686,10 +2687,15 @@ compile_index(PredEntry *ap)
   int NClauses = ap->cs.p_code.NOfClauses;
   ClauseDef *cls = (ClauseDef *)H;
   CELL *top = (CELL *) TR;
+
   /* only global variable I use directly */
   labelno = 1;
 
-  if (cls+NClauses > (ClauseDef *)(ASP-4096)) {
+  Yap_Error_Size = NClauses*sizeof(ClauseDef);
+  /* reserve double the space for compiler */
+  if (cls+2*NClauses > (ClauseDef *)(ASP-4096)) {
+    /* tell how much space we need */
+    Yap_Error_Size += NClauses*sizeof(ClauseDef);
     /* grow stack */
     longjmp(Yap_CompilerBotch,3);
   }
@@ -2710,10 +2716,10 @@ Yap_PredIsIndexable(PredEntry *ap)
 {
   yamop *indx_out;
 
+  Yap_Error_Size = 0;
   if (setjmp(Yap_CompilerBotch) == 3) {
-    /* just duplicate the stack */
     restore_machine_regs();
-    Yap_gc(ap->ArityOfPE, ENV, CP);
+    Yap_gcl(Yap_Error_Size, ap->ArityOfPE, ENV, CP);
   }
  restart_index:
   Yap_ErrorMessage = NULL;
@@ -2729,7 +2735,7 @@ Yap_PredIsIndexable(PredEntry *ap)
   CurrentPred = ap;
   IPredArity = ap->ArityOfPE;
   if ((indx_out = Yap_assemble(ASSEMBLING_INDEX)) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_Error_Size)) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return NULL;
     }
diff --git a/C/init.c b/C/init.c
index f4a85da22..facd950d3 100644
--- a/C/init.c
+++ b/C/init.c
@@ -84,6 +84,7 @@ ADDR            Yap_HeapBase,
 char           *Yap_ErrorMessage;	/* used to pass error messages */
 Term              Yap_Error_Term;	/* used to pass error terms */
 yap_error_number  Yap_Error_TYPE;	/* used to pass the error */
+UInt             Yap_Error_Size;	/* used to pass a size associated with an error */
 
 /********* readline support	*****/
 #if HAVE_LIBREADLINE
diff --git a/C/iopreds.c b/C/iopreds.c
index 542039596..0807450c2 100644
--- a/C/iopreds.c
+++ b/C/iopreds.c
@@ -2004,7 +2004,7 @@ p_open_mem_read_stream (void)   /* $open_mem_read_stream(+List,-Stream) */
     }
   }
   while ((nbuf = (char *)Yap_AllocAtomSpace((sl+1)*sizeof(char))) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, (sl+1)*sizeof(char))) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     }
@@ -2058,7 +2058,7 @@ p_open_mem_write_stream (void)   /* $open_mem_write_stream(-Stream) */
   extern int Yap_page_size;
 
   while ((nbuf = (char *)Yap_AllocAtomSpace(Yap_page_size*sizeof(char))) == NULL) {
-    if (!Yap_growheap(FALSE)) {
+    if (!Yap_growheap(FALSE, Yap_page_size*sizeof(char))) {
       Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
       return(FALSE);
     }
@@ -4833,7 +4833,7 @@ p_char_conversion(void)
       return(TRUE);
     CharConversionTable2 = Yap_AllocCodeSpace(NUMBER_OF_CHARS*sizeof(char));
     while (CharConversionTable2 == NULL) {
-      if (!Yap_growheap(FALSE)) {
+      if (!Yap_growheap(FALSE, NUMBER_OF_CHARS*sizeof(char))) {
 	Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	return(FALSE);
       }
diff --git a/C/save.c b/C/save.c
index 23e29e4c2..cd69f4bd0 100644
--- a/C/save.c
+++ b/C/save.c
@@ -650,7 +650,7 @@ check_header(CELL *info, CELL *ATrail, CELL *AStack, CELL *AHeap)
   if (Yap_ErrorMessage)
      return(FAIL_RESTORE);
   while (Yap_HeapBase != NULL && hp_size > Unsigned(AuxTop) - Unsigned(Yap_HeapBase)) {
-    if(!Yap_growheap(FALSE)) {
+    if(!Yap_growheap(FALSE, hp_size)) {
       return(FAIL_RESTORE);      
     }
   }
diff --git a/C/stdpreds.c b/C/stdpreds.c
index a240ea22a..47cffd084 100644
--- a/C/stdpreds.c
+++ b/C/stdpreds.c
@@ -853,7 +853,7 @@ p_atom_concat(void)
     sz = strlen(atom_str);
     if (cptr+sz >= top-1024) {
       Yap_ReleasePreAllocCodeSpace((ADDR)cpt0);
-      if (!Yap_growheap(FALSE)) {
+      if (!Yap_growheap(FALSE, sz+1024)) {
 	Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	return(FALSE);
       }
diff --git a/C/utilpreds.c b/C/utilpreds.c
index a810694a5..88aa9596d 100644
--- a/C/utilpreds.c
+++ b/C/utilpreds.c
@@ -316,7 +316,7 @@ CopyTerm(Term inp) {
 	  t = Deref(ARG1);
 	  goto restart_attached;
 	} else { /* handle overflow */
-	  if (!Yap_growheap(FALSE)) {
+	  if (!Yap_growheap(FALSE, 0)) {
 	    Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	    return(FALSE);
 	  }
@@ -352,7 +352,7 @@ CopyTerm(Term inp) {
 	  t = Deref(ARG1);
 	  goto restart_list;
 	} else { /* handle overflow */
-	  if (!Yap_growheap(FALSE)) {
+	  if (!Yap_growheap(FALSE, 0)) {
 	    Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	    return(FALSE);
 	  }
@@ -387,7 +387,7 @@ CopyTerm(Term inp) {
 	  t = Deref(ARG1);
 	  goto restart_appl;
 	} else { /* handle overflow */
-	  if (!Yap_growheap(FALSE)) {
+	  if (!Yap_growheap(FALSE, 0)) {
 	    Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	    return(FALSE);
 	  }
@@ -625,7 +625,7 @@ CopyTermNoDelays(Term inp) {
 	t = Deref(ARG1);
 	goto restart_list;
       } else { /* handle overflow */
-	if (!Yap_growheap(FALSE)) {
+	if (!Yap_growheap(FALSE, 0)) {
 	  Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	  return(FALSE);
 	}
@@ -657,7 +657,7 @@ CopyTermNoDelays(Term inp) {
 	t = Deref(ARG1);
 	goto restart_appl;
       } else { /* handle overflow */
-	if (!Yap_growheap(FALSE)) {
+	if (!Yap_growheap(FALSE, 0)) {
 	  Yap_Error(SYSTEM_ERROR, TermNil, Yap_ErrorMessage);
 	  return(FALSE);
 	}
diff --git a/H/Yapproto.h b/H/Yapproto.h
index ae58488ab..6a8f31083 100644
--- a/H/Yapproto.h
+++ b/H/Yapproto.h
@@ -10,7 +10,7 @@
 * File:		Yap.proto						 *
 * mods:									 *
 * comments:	Function declarations for YAP				 *
-* version:      $Id: Yapproto.h,v 1.33 2003-03-20 15:10:17 vsc Exp $	 *
+* version:      $Id: Yapproto.h,v 1.34 2003-05-19 13:04:08 vsc Exp $	 *
 *************************************************************************/
 
 /* prototype file for Yap */
@@ -154,7 +154,7 @@ void	STD_PROTO(Yap_trust_last,(void));
 /* grow.c */
 Int     STD_PROTO(Yap_total_stack_shift_time,(void));
 void    STD_PROTO(Yap_InitGrowPreds, (void));
-int     STD_PROTO(Yap_growheap,      (int));
+int     STD_PROTO(Yap_growheap,      (int, UInt));
 int     STD_PROTO(Yap_growstack,     (long));
 int     STD_PROTO(Yap_growtrail,     (long));
 int     STD_PROTO(Yap_growglobal,    (CELL **));
@@ -164,6 +164,7 @@ Int  STD_PROTO(Yap_total_gc_time,(void));
 void STD_PROTO(Yap_init_gc,(void));
 int  STD_PROTO(Yap_is_gc_verbose, (void));
 int  STD_PROTO(Yap_gc, (Int, CELL *, yamop *));
+int  STD_PROTO(Yap_gcl, (UInt, Int, CELL *, yamop *));
 
 /* init.c */
 #ifdef DEBUG
diff --git a/Makefile.in b/Makefile.in
index 04ff29868..481aeca4f 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -90,7 +90,7 @@ TEXI2PDF=texi2pdf
 #4.1VPATH=@srcdir@:@srcdir@/OPTYap
 CWD=$(PWD)
 #
-VERSION=Yap-4.5.0
+VERSION=Yap-4.5.1
 #
 
 TAG_HEADERS=  Tags_32bits.h Tags_32Ops.h Tags_32LowTag.h\
diff --git a/README b/README
index 33c4cb7e3..aa2ae64aa 100644
--- a/README
+++ b/README
@@ -1,10 +1,10 @@
 
 
 
-			README for Yap 4.3
+			README for Yap 4.5
 
 
-This directory contains a release of the Yap 4.2 Prolog system,
+This directory contains a release of the Yap 4.t Prolog system,
 originally developed at the Universidade do Porto by Luis Damas and
 Vitor Santos Costa, with contributions from the Edinburgh Prolog
 library, the C-Prolog manual authors, Ricardo Rocha, and many
diff --git a/m4/Yap.h.m4 b/m4/Yap.h.m4
index 1e2617c3a..f33398a12 100644
--- a/m4/Yap.h.m4
+++ b/m4/Yap.h.m4
@@ -10,7 +10,7 @@
 * File:		Yap.h.m4						 *
 * mods:									 *
 * comments:	main header file for YAP				 *
-* version:      $Id: Yap.h.m4,v 1.44 2003-04-30 17:44:18 vsc Exp $	 *
+* version:      $Id: Yap.h.m4,v 1.45 2003-05-19 13:04:09 vsc Exp $	 *
 *************************************************************************/
 
 #include "config.h"
@@ -485,6 +485,7 @@ typedef enum {
 extern char    *Yap_ErrorMessage;	/* used to pass error messages		*/
 extern Term     Yap_Error_Term;	/* used to pass error terms */
 extern yap_error_number  Yap_Error_TYPE;	/* used to pass the error */
+extern UInt  Yap_Error_Size;	/* used to pass the error */
 
 typedef enum {
   YAP_INT_BOUNDED_FLAG = 0,
diff --git a/pl/directives.yap b/pl/directives.yap
index bff97796c..ef54bd3f7 100644
--- a/pl/directives.yap
+++ b/pl/directives.yap
@@ -133,11 +133,14 @@ yap_flag(gc,on) :- !, '$set_value'('$gc',true).
 yap_flag(gc,off) :- !, '$set_value'('$gc',[]).
 
 yap_flag(gc_margin,N) :- 
-	var(N) -> 
-		 '$get_value'('$gc_margin',N)
-        ;
-        integer(N) ->
-	         '$set_value'('$gc_margin',N).
+	( var(N) -> 
+	    '$get_value'('$gc_margin',N)
+	;
+	  integer(N), N >0  ->
+	    '$set_value'('$gc_margin',N)
+	;
+	    '$do_error'(domain_error(flag_value,gc_margin+X),yap_flag(gc_margin,X))
+	).
 yap_flag(gc_trace,V) :-
 	var(V), !,
 	'$get_value'('$gc_trace',N1),