diff --git a/lib/PDL/Core.xs b/lib/PDL/Core.xs
index 1189d72da..292246963 100644
--- a/lib/PDL/Core.xs
+++ b/lib/PDL/Core.xs
@@ -47,7 +47,7 @@
 #define setflag(reg,flagval,val) (val?(reg |= flagval):(reg &= ~flagval))
 
 Core PDL; /* Struct holding pointers to shared C routines */
-static char *type_names[] = {
+static char *type_names[PDL_NTYPES+1] = {
 #define X(symbol, ctype, ppsym, shortctype, defbval, realctype, convertfunc, ...) \
   #convertfunc,
   PDL_TYPELIST_ALL(X)
@@ -835,7 +835,7 @@ BOOT:
    PDL_TYPELIST_ALL(X)
 #undef X
   PDL.type_names = type_names;
-  PDL.ntypes = sizeof(type_names) / sizeof(type_names[0]) - 1;
+  PDL.ntypes = PDL_NTYPES;
   /* "Publish" pointer to this structure in perl variable for use
      by other modules */
   sv_setiv(get_sv("PDL::SHARE",TRUE|GV_ADDMULTI), PTR2IV(&PDL));
diff --git a/lib/PDL/Core/pdl.h.PL b/lib/PDL/Core/pdl.h.PL
index bcb8f9d35..70dba95da 100644
--- a/lib/PDL/Core/pdl.h.PL
+++ b/lib/PDL/Core/pdl.h.PL
@@ -79,10 +79,38 @@ for my $type (PDL::Types::types()) {
   my $expr2 = !$type->usenan ? 1 : $type->isfinite('x') . '?1:0';
   print OUT "#define PDL_ISFINITE_$ppsym(x) ($expr2)\n";
 }
+print OUT "#define PDL_NTYPES (@{[0+PDL::Types::types()]})\n";
 
 print OUT sprintf qq{#line %d "%s"\n}, __LINE__ + 2,  __FILE__;
 print OUT <<'EOF';
 
+#define PDL_BITFIELD_ENT uint64_t
+#define PDL_BITFIELD_ENTSIZE (sizeof(PDL_BITFIELD_ENT))
+#define PDL_BITFIELD_SIZE(nbits) \
+  (((nbits) + PDL_BITFIELD_ENTSIZE - 1) / PDL_BITFIELD_ENTSIZE)
+#define PDL_BITFIELD_ENTOF(vec, bit) (vec[bit/PDL_BITFIELD_ENTSIZE])
+#define PDL_BITFIELD_BITOFFSET(bit) (bit % PDL_BITFIELD_ENTSIZE)
+#define PDL_BITFIELD_BITMASK(bit) (1 << PDL_BITFIELD_BITOFFSET(bit))
+#define PDL_BITFIELD_ISSET(vec, bit) \
+  ((PDL_BITFIELD_ENTOF(vec, bit) & PDL_BITFIELD_BITMASK(bit)) ? 1 : 0)
+#define PDL_BITFIELD_SET(vec, bit) do { \
+    PDL_Indx PDL_BITFIELD_i = bit; \
+    PDL_BITFIELD_ENTOF(vec, PDL_BITFIELD_i) |= PDL_BITFIELD_BITMASK(PDL_BITFIELD_i); \
+  } while (0)
+#define PDL_BITFIELD_CLR(vec, bit) do { \
+    PDL_Indx PDL_BITFIELD_i = bit; \
+    PDL_BITFIELD_ENTOF(vec, PDL_BITFIELD_i) &= ~PDL_BITFIELD_BITMASK(PDL_BITFIELD_i); \
+  } while (0)
+#define PDL_BITFIELD_SETTO(vec, bit, cond) do { \
+    PDL_Indx PDL_BITFIELD_i = bit; \
+    if (cond) PDL_BITFIELD_SET(vec, PDL_BITFIELD_i); else PDL_BITFIELD_CLR(vec, PDL_BITFIELD_i); \
+  } while (0)
+#define PDL_BITFIELD_ZEROISE(vec, nbits) do { \
+    PDL_Indx PDL_BITFIELD_i, PDL_BITFIELD_n = PDL_BITFIELD_SIZE(nbits); \
+    for (PDL_BITFIELD_i = 0; PDL_BITFIELD_i < PDL_BITFIELD_n; PDL_BITFIELD_i++) \
+      vec[PDL_BITFIELD_i] = 0; \
+  } while (0)
+
 #define X(sym, ...) \
   , sym
 typedef enum {
diff --git a/lib/PDL/Core/pdlapi.c b/lib/PDL/Core/pdlapi.c
index 788fc0951..80028bb8c 100644
--- a/lib/PDL/Core/pdlapi.c
+++ b/lib/PDL/Core/pdlapi.c
@@ -727,11 +727,12 @@ pdl_error pdl_make_trans_mutual(pdl_trans *trans)
   PDLDEBUG_f(printf("make_trans_mutual dataflow=%d disable_back=%d\n", (int)dataflow, (int)disable_back));
   if (dataflow && disable_back)
     trans->flags &= ~PDL_ITRANS_DO_DATAFLOW_B;
-  char wasnull[npdls];
+  PDL_BITFIELD_ENT wasnull[PDL_BITFIELD_SIZE(npdls)];
+  PDL_BITFIELD_ZEROISE(wasnull, npdls);
   for (i=nparents; i<npdls; i++) {
     pdl *child = pdls[i];
-    wasnull[i] = !!(child->state & PDL_NOMYDIMS);
-    PDLDEBUG_f(printf("make_trans_mutual child=%p wasnull[%"IND_FLAG"]=%d\n", child, i, (int)wasnull[i]));
+    if (child->state & PDL_NOMYDIMS) PDL_BITFIELD_SET(wasnull, i);
+    PDLDEBUG_f(printf("make_trans_mutual child=%p wasnull[%"IND_FLAG"]=%d\n", child, i, PDL_BITFIELD_ISSET(wasnull, i)));
     if (dataflow) {
       /* This is because for "+=" (a = a + b) we must check for
          previous parent transformations and mutate if they exist
@@ -740,8 +741,8 @@ pdl_error pdl_make_trans_mutual(pdl_trans *trans)
       child->state |= PDL_PARENTDIMSCHANGED | ((trans->flags & PDL_ITRANS_ISAFFINE) ? 0 : PDL_PARENTDATACHANGED);
       PDLDEBUG_f(printf("make_trans_mutual after change="); pdl_dump_flags_fixspace(child->state, 0, PDL_FLAGS_PDL));
     }
-    if (!child->trans_parent || wasnull[i]) child->trans_parent = trans;
-    if (wasnull[i])
+    if (!child->trans_parent || PDL_BITFIELD_ISSET(wasnull, i)) child->trans_parent = trans;
+    if (PDL_BITFIELD_ISSET(wasnull, i))
       child->state = (child->state & ~PDL_NOMYDIMS) | PDL_MYDIMS_TRANS;
   }
   if (!dataflow) {
@@ -752,9 +753,9 @@ pdl_error pdl_make_trans_mutual(pdl_trans *trans)
       for (i=vtable->nparents; i<vtable->npdls; i++) {
         pdl *child = trans->pdls[i];
         char isvaffine = !!PDL_VAFFOK(child);
-        PDLDEBUG_f(printf("make_trans_mutual isvaffine=%d wasnull=%d\n", (int)isvaffine, (int)wasnull[i]));
-        if (!isvaffine || wasnull[i])
-          CHANGED(child, wasnull[i] ? PDL_PARENTDIMSCHANGED : PDL_PARENTDATACHANGED, 0);
+        PDLDEBUG_f(printf("make_trans_mutual isvaffine=%d wasnull=%d\n", (int)isvaffine, PDL_BITFIELD_ISSET(wasnull, i)));
+        if (!isvaffine || PDL_BITFIELD_ISSET(wasnull, i))
+          CHANGED(child, PDL_BITFIELD_ISSET(wasnull, i) ? PDL_PARENTDIMSCHANGED : PDL_PARENTDATACHANGED, 0);
         if (isvaffine)
           CHANGED(child->vafftrans->from,PDL_PARENTDATACHANGED,0);
       }
@@ -1115,10 +1116,11 @@ static inline pdl_error pdl__transtype_select(
         "%s: ndarray %s must be real, but is type %s",
         vtable->name, vtable->par_names[i], PDL_TYPENAME(dtype));
   }
-  char type_avail[PDL.ntypes]; for (i=0; i<PDL.ntypes; i++) type_avail[i] = 0;
+  PDL_BITFIELD_ENT type_avail[PDL_BITFIELD_SIZE(PDL_NTYPES)];
+  PDL_BITFIELD_ZEROISE(type_avail, PDL_NTYPES);
   pdl_datatypes last_dtype = PDL_INVALID;
   for (i=0; vtable->gentypes[i] != PDL_INVALID; i++)
-    type_avail[last_dtype = vtable->gentypes[i]] = 1;
+    PDL_BITFIELD_SET(type_avail, last_dtype = vtable->gentypes[i]);
   if (vtable->gentypes[0] == last_dtype) {
     *retval = vtable->gentypes[0]; /* only one allowed type, use that */
     return PDL_err;
@@ -1130,12 +1132,12 @@ static inline pdl_error pdl__transtype_select(
       !(flags & (PDL_PARAM_ISIGNORE|PDL_PARAM_ISTYPED|PDL_PARAM_ISCREATEALWAYS))
     ) {
       pdl_datatypes new_transtype = PDL_TYPE_ADJUST_FROM_SUPPLIED(pdl->datatype, flags);
-      if (new_transtype != PDL_INVALID && type_avail[new_transtype] && *retval < new_transtype)
+      if (new_transtype != PDL_INVALID && PDL_BITFIELD_ISSET(type_avail, new_transtype) && *retval < new_transtype)
         *retval = new_transtype;
     }
     if (i == vtable->nparents && *retval != PDL_INVALID) return PDL_err;
   }
-  if (*retval == PDL_INVALID || !type_avail[*retval]) *retval = last_dtype;
+  if (*retval == PDL_INVALID || !PDL_BITFIELD_ISSET(type_avail, *retval)) *retval = last_dtype;
   return PDL_err;
 }
 
diff --git a/lib/PDL/Core/pdlcore.h b/lib/PDL/Core/pdlcore.h
index b897f9191..252e11518 100644
--- a/lib/PDL/Core/pdlcore.h
+++ b/lib/PDL/Core/pdlcore.h
@@ -23,10 +23,10 @@
 
 #ifdef PDL_IN_CORE
 #define PDL_CORE_(func) pdl_##func
-#define PDL_TYPENAME(t) (!PDL.type_names ? "ERROR: type_names not set" : (t < 0 || t >= PDL.ntypes) ? "INVALID" : PDL.type_names[t])
+#define PDL_TYPENAME(t) (!PDL.type_names ? "ERROR: type_names not set" : (t < 0 || t >= PDL_NTYPES) ? "INVALID" : PDL.type_names[t])
 #else
 #define PDL_CORE_(func) PDL->func
-#define PDL_TYPENAME(t) (!PDL->type_names ? "ERROR: type_names not set" : (t < 0 || t >= PDL->ntypes) ? "INVALID" : PDL->type_names[t])
+#define PDL_TYPENAME(t) (!PDL->type_names ? "ERROR: type_names not set" : (t < 0 || t >= PDL_NTYPES) ? "INVALID" : PDL->type_names[t])
 #endif
 
 #define PDL_RECURSE_CHECK(var) \