Merge pull request #756 from PierUgit/popcnt2

Replaced btest() by popcnt() in bit_count_large()

Author: jvdp1

example/bitsets/example_bitsets_bit_count.f90

@@ -3,6 +3,9 @@ program example_bit_count
   character(*), parameter :: &
     bits_0 = '0000000000000000000'
   type(bitset_64) :: set0
+  type(bitset_large) :: set1
+  logical, allocatable :: logi(:)
+  
   call set0%from_string(bits_0)
   if (set0%bit_count() == 0) then
     write (*, *) "FROM_STRING interpreted "// &
@@ -12,4 +15,11 @@ program example_bit_count
   if (set0%bit_count() == 1) then
     write (*, *) "BIT_COUNT interpreted SET0's value properly."
   end if
+  
+  allocate( logi(1000), source=.false.)
+  logi(1::7) = .true.
+  set1 = logi
+  if (set1%bit_count() == count(logi)) then
+    write (*, *) "BIT_COUNT interpreted SET1's value properly."
+  end if
 end program example_bit_count

src/stdlib_bitsets_large.fypp

@@ -144,19 +144,13 @@ contains
         integer(bits_kind)              ::  bit_count
         class(bitset_large), intent(in) :: self
 
-        integer(bits_kind) :: block_, pos
+        integer(bits_kind) :: nblocks, pos
 
-        bit_count = 0
-        do block_ = 1_bits_kind, size(self % blocks, kind=bits_kind) - 1
-            do pos = 0, block_size-1
-                if ( btest( self % blocks(block_), pos ) ) &
-                    bit_count = bit_count + 1
-            end do
-
-        end do
+        nblocks = size( self % blocks, kind=bits_kind )
+        bit_count = sum( popcnt( self % blocks(1:nblocks-1) ) )
 
-        do pos = 0_bits_kind, self % num_bits - (block_-1)*block_size - 1
-            if ( btest( self % blocks(block_), pos ) ) bit_count = bit_count + 1
+        do pos = 0_bits_kind, self % num_bits - (nblocks-1)*block_size - 1
+            if ( btest( self % blocks(nblocks), pos ) ) bit_count = bit_count + 1
         end do
 
     end function bit_count_large