diff --git a/src/util/supervector/supervector.hpp b/src/util/supervector/supervector.hpp
index d245e0ca..bd7fd18a 100644
--- a/src/util/supervector/supervector.hpp
+++ b/src/util/supervector/supervector.hpp
@@ -32,6 +32,7 @@
 
 #include <cstdint>
 #include <cstdio>
+#include <type_traits>
 
 #if defined(ARCH_IA32) || defined(ARCH_X86_64)
 #include "util/supervector/arch/x86/types.hpp"
@@ -88,48 +89,63 @@ using m1024_t = SuperVector<128>;
 template <int T>
 struct BaseVector
 {
-  static const bool is_valid = false;  // for template matches specialisation
-  using type                 = void;
-  using movemask_type        = uint32_t;
-  using previous_type        = void;
+  static constexpr bool      is_valid = false;
+  static constexpr u16           size = 8;
+  using                          type = void;
+  using                 movemask_type = void;
+  static constexpr bool  has_previous = false;
+  using                 previous_type = void;
+  static constexpr u16  previous_size = 4;
 };
 
 template <>
 struct BaseVector<128>
 {
-  static constexpr bool     is_valid  = true;
-  static constexpr uint16_t size      = 128;
-  using type                          = void;
-  using movemask_type                 = u64a;
+  static constexpr bool      is_valid = true;
+  static constexpr u16           size = 128;
+  using                          type = void;
+  using                 movemask_type = u64a;
+  static constexpr bool  has_previous = true;
+  using                 previous_type = m512;
+  static constexpr u16  previous_size = 64;
 };
 
 template <>
 struct BaseVector<64>
 {
-  static constexpr bool     is_valid  = true;
-  static constexpr uint16_t size      = 64;
-  using type                          = m512;
-  using movemask_type                 = u64a;
+  static constexpr bool      is_valid = true;
+  static constexpr u16           size = 64;
+  using                          type = m512;
+  using                 movemask_type = u64a;
+  static constexpr bool  has_previous = true;
+  using                 previous_type = m256;
+  static constexpr u16  previous_size = 32;
 };
 
 // 128 bit implementation
 template <>
 struct BaseVector<32>
 {
-  static constexpr bool     is_valid  = true;
-  static constexpr uint16_t size      = 32;
-  using type                          = m256;
-  using movemask_type                 = u32;
+  static constexpr bool      is_valid = true;
+  static constexpr u16           size = 32;
+  using                          type = m256;
+  using                 movemask_type = u32;
+  static constexpr bool  has_previous = true;
+  using                 previous_type = m128;
+  static constexpr u16  previous_size = 16;
 };
 
 // 128 bit implementation
 template <>
 struct BaseVector<16>
 {
-  static constexpr bool     is_valid  = true;
-  static constexpr uint16_t size      = 16;
-  using type                          = m128;
-  using movemask_type                 = u32;
+  static constexpr bool      is_valid = true;
+  static constexpr u16           size = 16;
+  using                          type = m128;
+  using                 movemask_type = u32;
+  static constexpr bool  has_previous = false;
+  using                 previous_type = u64a;
+  static constexpr u16  previous_size = 8;
 };
 
 template <uint16_t SIZE>
@@ -140,6 +156,7 @@ class SuperVector : public BaseVector<SIZE>
 public:
 
   using base_type      = BaseVector<SIZE>;
+  using previous_type  = typename BaseVector<SIZE>::previous_type;
 
   union {
     typename BaseVector<16>::type ALIGN_ATTR(BaseVector<16>::size) v128[SIZE / BaseVector<16>::size];
@@ -164,6 +181,9 @@ public:
   template<typename T>
   SuperVector(T const other);
 
+  SuperVector(SuperVector<SIZE/2> const lo, SuperVector<SIZE/2> const hi);
+  SuperVector(previous_type const lo, previous_type const hi);
+
   static SuperVector dup_u8 (uint8_t  other) { return {other}; };
   static SuperVector dup_s8 (int8_t   other) { return {other}; };
   static SuperVector dup_u16(uint16_t other) { return {other}; };
@@ -208,38 +228,38 @@ public:
   static SuperVector Zeroes();
 
   #if defined(DEBUG)
-  void print8(const char *label) {
+  void print8(const char *label) const {
       printf("%12s: ", label);
       for(s16 i=SIZE-1; i >= 0; i--)
           printf("%02x ", u.u8[i]);
       printf("\n");
   }
 
-  void print16(const char *label) {
+  void print16(const char *label) const {
       printf("%12s: ", label);
       for(s16 i=SIZE/sizeof(u16)-1; i >= 0; i--)
           printf("%04x ", u.u16[i]);
       printf("\n");
   }
 
-  void print32(const char *label) {
+  void print32(const char *label) const {
       printf("%12s: ", label);
       for(s16 i=SIZE/sizeof(u32)-1; i >= 0; i--)
           printf("%08x ", u.u32[i]);
       printf("\n");
   }
 
-  void print64(const char *label) {
+  void print64(const char *label) const {
       printf("%12s: ", label);
       for(s16 i=SIZE/sizeof(u64a)-1; i >= 0; i--)
           printf("%016lx ", u.u64[i]);
       printf("\n");
   }
 #else
-  void print8(const char *label UNUSED) {};
-  void print16(const char *label UNUSED) {};
-  void print32(const char *label UNUSED) {};
-  void print64(const char *label UNUSED) {};
+  void print8(const char *label UNUSED) const {};
+  void print16(const char *label UNUSED) const {};
+  void print32(const char *label UNUSED) const {};
+  void print64(const char *label UNUSED) const {};
 #endif
 };