Pull subtracting_span_iterator out into separate file + test.

persistent-data/space-maps/subtracting_span_iterator.h

@@ -0,0 +1,101 @@
+#ifndef SPAN_ITERATOR_H
+#define SPAN_ITERATOR_H
+
+#include "persistent-data/space_map.h"
+
+#include <set>
+
+//----------------------------------------------------------------
+
+namespace persistent_data {
+	// FIXME: rewrite with tests using the run_list stuff.
+	class subtracting_span_iterator : public space_map::span_iterator {
+	public:
+		typedef set<block_address> block_set;
+		typedef space_map::span span;
+
+		subtracting_span_iterator(span_iterator &sub_it,
+					  block_set const &forbidden_blocks)
+			: sub_it_(sub_it),
+			  forbidden_blocks_(forbidden_blocks),
+			  current_begin_() {
+		}
+
+		virtual maybe_span first() {
+			current_span_ = sub_it_.first();
+
+			if (current_span_)
+				current_begin_ = current_span_->first;
+
+			return next();
+		}
+
+		virtual maybe_span next() {
+			maybe_span r;
+
+			while (more_spans()) {
+				r = next_();
+				if (r)
+					break;
+			}
+
+			return r;
+		}
+
+	private:
+		bool more_spans() const {
+			return current_span_;
+		}
+
+		bool span_consumed() const {
+			return current_begin_ == current_span_->second;
+		}
+
+		bool forbidden_block(block_address b) const {
+			return forbidden_blocks_.count(b) > 0;
+		}
+
+		void skip_forbidden_blocks() {
+			while (!span_consumed() && forbidden_block(current_begin_))
+				current_begin_++;
+		}
+
+		span get_span() {
+			block_address b = current_begin_;
+
+			while (!span_consumed() && !forbidden_block(current_begin_))
+				current_begin_++;
+
+			return span(b, current_begin_);
+		}
+
+		void get_current_span_from_sub_it() {
+			current_span_ = sub_it_.next();
+			current_begin_ = current_span_->first;
+		}
+
+		maybe_span next_() {
+			if (span_consumed())
+				get_current_span_from_sub_it();
+
+			if (!more_spans())
+				return maybe_span();
+
+			skip_forbidden_blocks();
+
+			if (!span_consumed())
+				return maybe_span(get_span());
+			else
+				return maybe_span();
+		}
+
+		span_iterator &sub_it_;
+		block_set const &forbidden_blocks_;
+		maybe_span current_span_;
+		block_address current_begin_;
+	};
+}
+
+//----------------------------------------------------------------
+
+#endif