bitvect: add a is_subset_of method.

* src/misc/bitvect.hh: New method.
* src/tgbatest/bitvect.cc, src/tgbatest/bitvect.test: Test it.

src/misc/bitvect.hh

@@ -298,6 +298,23 @@ namespace spot
       return *this;
     }
 
+    bool is_subset_of(const bitvect& other) const
+    {
+      assert(other.block_count_ >= block_count_);
+
+      size_t i;
+      for (i = 0; i < block_count_ - 1; ++i)
+	if ((storage_[i] & other.storage_[i]) != other.storage_[i])
+	  return false;
+
+      // The last block might not be fully used, compare only the
+      // relevant portion.
+      const size_t bpb = 8 * sizeof(bitvect::block_t);
+      block_t mask = (1UL << (size() % bpb)) - 1;
+      return ((storage_[i] & mask & other.storage_[i])
+	      == (other.storage_[i] & mask));
+    }
+
     bool operator==(const bitvect& other) const
     {
       if (other.size_ != size_)

src/tgbatest/bitvect.cc

@@ -64,6 +64,9 @@ int main()
   *x |= *w;
   ECHO(x);
 
+  std::cout << "subset? " << w->is_subset_of(*x)
+	    << ' ' << w->is_subset_of(*v) << '\n';
+
   for (size_t i = 0; i < 30; ++i)
     w->push_back((i & 3) == 0);
   ECHO(w);

src/tgbatest/bitvect.test

@@ -42,6 +42,7 @@ w: 000000000010110000000000000000100000000001
 
 x: 000000000000000000000000000000000000000000000000000000000000100000000010000
 x: 000000000010110000000000000000100000000001000000000000000000100000000010000
+subset? 1 0
 w: 000000000010110000000000000000100000000001100010001000100010001000100010
 x: 000000000010110000000000000000100000000001000000000000000000000000000010000
 x: 111111111111111111111111111111111111111111111111111111111111111111111111111