Revert "Use a safer expression to set N lowest bits of an integer"

This reverts commit 32371cf.
krivenko · Jul 18, 2024 · 1dc15be · 1dc15be
1 parent 8860314
commit 1dc15be
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Showing 6 changed files with 16 additions and 24 deletions.
diff --git a/include/libcommute/loperator/monomial_action_boson.hpp b/include/libcommute/loperator/monomial_action_boson.hpp
@@ -92,7 +92,7 @@ template <> class monomial_action<boson> {
         bit_range_t const& bit_range = hs.bit_range(es);
         int shift = bit_range.first;
         int n_bits = bit_range.second - bit_range.first + 1;
-        sv_index_type n_max = (~sv_index_type(0)) >> (sv_index_width - n_bits);
+        sv_index_type n_max = (sv_index_type(1) << n_bits) - 1;
 
         sqr_roots_size = std::max(sqr_roots_size, n_max + 1);
 
@@ -108,12 +108,12 @@ template <> class monomial_action<boson> {
         auto n_change = static_cast<std::int64_t>(dagger ? power : -power);
         std::int64_t state_change = n_change * (std::int64_t(1) << shift);
 
-        updates_.emplace_back(single_boson_update_t{
-            shift,
-            (~sv_index_type(0)) >> (sv_index_width - n_bits),
-            n_change,
-            n_max,
-            state_change});
+        updates_.emplace_back(
+            single_boson_update_t{shift,
+                                  (sv_index_type(1) << n_bits) - 1,
+                                  n_change,
+                                  n_max,
+                                  state_change});
 
         power = 1;
       } else

diff --git a/include/libcommute/loperator/monomial_action_spin.hpp b/include/libcommute/loperator/monomial_action_spin.hpp
@@ -101,12 +101,12 @@ template <> class monomial_action<spin> {
             g.multiplicity() % 2 == 0 ? (s + 0.5) * (s + 0.5) : s * (s + 1);
         sqr_roots_size = std::max(sqr_roots_size, ss + 1);
 
-        updates_.emplace_back(single_spin_update_t{
-            sv_index_type(2 * s),
-            shift,
-            (~sv_index_type(0)) >> (sv_index_width - n_bits),
-            g.component(),
-            power});
+        updates_.emplace_back(
+            single_spin_update_t{sv_index_type(2 * s),
+                                 shift,
+                                 (sv_index_type(1) << n_bits) - 1,
+                                 g.component(),
+                                 power});
 
         power = 1;
       } else

diff --git a/include/libcommute/loperator/state_vector.hpp b/include/libcommute/loperator/state_vector.hpp
@@ -17,7 +17,6 @@
 
 #include <algorithm>
 #include <cstdint>
-#include <limits>
 #include <utility>
 #include <vector>
 
@@ -26,10 +25,6 @@ namespace libcommute {
 // Type of index into a state vector
 using sv_index_type = std::uint64_t;
 
-// Bit width of the state index type
-static constexpr int sv_index_width =
-    std::numeric_limits<sv_index_type>::digits;
-
 //
 // Implementation of the StateVector interface for std::vector
 //

diff --git a/test/monomial_action_boson.cpp b/test/monomial_action_boson.cpp
@@ -98,8 +98,7 @@ TEST_CASE("Action of a bosonic monomial on an index",
 
   std::vector<sv_index_type> in_index_list(1 << n_op_bits);
   for(unsigned int i = 0; i < in_index_list.size(); i++)
-    in_index_list[i] = (i << n_pad_bits) +
-                       (~sv_index_type(0) >> (sv_index_width - n_pad_bits));
+    in_index_list[i] = (i << n_pad_bits) + (1 << n_pad_bits) - 1;
 
   SECTION("No operators") {
     mon_type mon;

diff --git a/test/monomial_action_fermion.cpp b/test/monomial_action_fermion.cpp
@@ -72,8 +72,7 @@ TEST_CASE("Action of a fermionic monomial on an index",
 
   std::vector<sv_index_type> in_index_list(1 << n_ops);
   for(unsigned int i = 0; i < in_index_list.size(); i++)
-    in_index_list[i] = (i << n_pad_bits) +
-                       (~sv_index_type(0) >> (sv_index_width - n_pad_bits));
+    in_index_list[i] = (i << n_pad_bits) + (1 << n_pad_bits) - 1;
 
   SECTION("No operators") {
     mon_type mon;

diff --git a/test/monomial_action_spin.cpp b/test/monomial_action_spin.cpp
@@ -110,8 +110,7 @@ TEST_CASE("Action of a spin monomial on an index", "[monomial_action_spin]") {
   for(sv_index_type n12 : {0, 1}) {
     for(sv_index_type n1 : {0, 1, 2}) {
       for(sv_index_type n32 : {0, 1, 2, 3}) {
-        sv_index_type index =
-            ~sv_index_type(0) >> (sv_index_width - n_pad_bits);
+        sv_index_type index = (1 << n_pad_bits) - 1;
         index += n12 << n_pad_bits;
         index += n1 << (n_pad_bits + 1);
         index += n32 << (n_pad_bits + 3);