base: add flex page iterator

Issue #8

base/include/base/flex_iterator.h

@@ -0,0 +1,113 @@
+/*
+ * \brief  Flexpage iterator
+ * \author Alexander Boettcher
+ * \date   2013-01-07
+ */
+
+/*
+ * Copyright (C) 2013-2013 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__BASE__FLEX_ITERATOR_H
+#define _INCLUDE__BASE__FLEX_ITERATOR_H
+
+#include <base/stdint.h>
+#include <util/misc_math.h>
+
+namespace Genode {
+
+	class Flexpage
+	{
+		public:
+
+			addr_t addr;
+			addr_t hotspot;
+			size_t log2_order;
+
+			Flexpage() : addr(~0UL), hotspot(0), log2_order(0) { }
+
+			Flexpage(addr_t a, addr_t h, size_t o)
+			: addr(a), hotspot(h), log2_order(o) { }
+
+			bool valid() { return addr != ~0UL; }
+	};
+
+
+	class Flexpage_iterator {
+
+		private:
+
+			addr_t _src_start, _src_size;
+			addr_t _dst_start, _dst_size;
+			addr_t _hotspot, _offset;
+
+			/**
+			 * Find least significant set bit in value
+			 */
+			inline addr_t
+			lsb_bit(addr_t const scan)
+			{
+				if (scan == 0)
+					return ~0UL;
+				return __builtin_ctzl(scan);
+			}
+
+		public:
+
+			Flexpage_iterator() { }
+
+			Flexpage_iterator(addr_t src_start, size_t src_size,
+			                  addr_t dst_start, size_t dst_size,
+			                  addr_t hotspot) :
+				_src_start(src_start), _src_size(src_size),
+			    _dst_start(dst_start), _dst_size(dst_size),
+				_hotspot(hotspot), _offset(0)
+			{ }
+
+			Flexpage page()
+			{
+				size_t const size = min (_src_size, _dst_size);
+
+				addr_t const from_end = _src_start + size;
+				addr_t const to_end   = _dst_start + size;
+
+				if (_offset >= size)
+					return Flexpage();
+
+				addr_t const from_curr = _src_start + _offset;
+				addr_t const to_curr   = _dst_start + _offset;
+
+				/*
+				 * The common alignment corresponds to the number of least
+				 * significant zero bits in both addresses.
+				 */
+				addr_t const common_bits = from_curr | to_curr;
+
+				/* find least set bit in common bits */
+				size_t order = lsb_bit(common_bits);
+				size_t max = (order == ~0UL) ? ~0UL : (1UL << order);
+
+				/* look if it still fits into both 'src' and 'dst' ranges */
+				if ((from_end - from_curr) < max) {
+					order = log2(from_end - from_curr);
+					order = (order == ~0UL) ? 12 : order;
+					max   = 1UL << order;
+				}
+
+				if ((to_end - to_curr) < max) {
+					order = log2(to_end - to_curr);
+					order = (order == ~0UL) ? 12 : order;
+				}
+
+				/* advance offset by current flexpage size */
+				_offset += (1UL << order);
+
+				return Flexpage(from_curr, _hotspot + _offset - (1UL << order), order);
+			}
+	};
+
+}
+#endif /* _INCLUDE__BASE__FLEX_ITERATOR_H */