Initial import of libdpf.

Co-authored-by: Cursor <cursoragent@cursor.com>

include/dpf/packed_lane.hpp

@@ -0,0 +1,75 @@
+/// @file dpf/packed_lane.hpp
+/// @brief Extract and deposit one `dpf::bit`, `dpf::twobit`, or `dpf::nyble`
+///        lane in a leaf node. Lane 0 is the low bits of the first byte.
+
+#ifndef LIBDPF_INCLUDE_DPF_PACKED_LANE_HPP__
+#define LIBDPF_INCLUDE_DPF_PACKED_LANE_HPP__
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+
+#include "hedley/hedley.h"
+
+#include "dpf/bit.hpp"
+#include "dpf/nyble.hpp"
+#include "dpf/twobit.hpp"
+
+namespace dpf
+{
+namespace packed
+{
+
+template <typename LaneT, typename LeafT>
+HEDLEY_ALWAYS_INLINE
+HEDLEY_NO_THROW
+HEDLEY_PURE
+LaneT extract_lane(const LeafT & leaf, std::size_t lane) noexcept
+{
+    constexpr unsigned bits = utils::packed_lane_bits_v<LaneT>;
+    static_assert(bits == 1 || bits == 2 || bits == 4,
+        "packed lane width must be 1, 2, or 4");
+    constexpr unsigned mask = (1u << bits) - 1u;
+    const auto * bytes = reinterpret_cast<const unsigned char *>(
+        std::addressof(leaf));
+    const std::size_t bit = lane * bits;
+    assert(bit / 8u < sizeof(LeafT));
+    const unsigned shift = static_cast<unsigned>(bit % 8u);
+    const unsigned val = (bytes[bit / 8u] >> shift) & mask;
+    return static_cast<LaneT>(val);
+}
+
+/// @brief zero `out` is the caller's job; this writes one lane and leaves
+///        every other lane untouched.
+template <typename LaneT, typename LeafT>
+HEDLEY_ALWAYS_INLINE
+HEDLEY_NO_THROW
+void deposit_lane(LeafT & leaf, std::size_t lane, LaneT value) noexcept
+{
+    constexpr unsigned bits = utils::packed_lane_bits_v<LaneT>;
+    static_assert(bits == 1 || bits == 2 || bits == 4,
+        "packed lane width must be 1, 2, or 4");
+    constexpr unsigned mask = (1u << bits) - 1u;
+    auto * bytes = reinterpret_cast<unsigned char *>(std::addressof(leaf));
+    const std::size_t bit = lane * bits;
+    assert(bit / 8u < sizeof(LeafT));
+    const unsigned shift = static_cast<unsigned>(bit % 8u);
+    const unsigned val = static_cast<unsigned>(value) & mask;
+    unsigned char & cell = bytes[bit / 8u];
+    cell = static_cast<unsigned char>((cell & ~(mask << shift)) | (val << shift));
+}
+
+template <typename NodeT, typename LaneT>
+HEDLEY_ALWAYS_INLINE
+HEDLEY_NO_THROW
+NodeT make_lane_node(std::size_t lane, LaneT value) noexcept
+{
+    NodeT node{};
+    deposit_lane<LaneT>(node, lane, value);
+    return node;
+}
+
+}  // namespace packed
+}  // namespace dpf
+
+#endif  // LIBDPF_INCLUDE_DPF_PACKED_LANE_HPP__