knothash stuff

knothash/include/knothash.hpp

@@ -0,0 +1,55 @@
+#ifndef KNOTHASH_HPP_
+#define KNOTHASH_HPP_
+
+#include <cstddef>
+#include <array>
+#include <algorithm>
+#include <string>
+
+namespace knothash {
+
+template <std::size_t N>
+auto reverser(std::array<std::uint8_t, N> & result, std::size_t cursor, std::size_t len) -> void {
+  auto leftside = N - cursor;
+  auto start = result.begin() + cursor;
+  if (len <= leftside) {
+    std::reverse(start, start + len);
+  } else {
+    auto rightside = len - leftside;
+    if (leftside < rightside) {
+      std::swap_ranges(start, result.end(), result.rend() - rightside);
+      std::reverse(result.begin(), result.begin() + (rightside-leftside));
+    } else {
+      std::swap_ranges(result.rend() - rightside, result.rend(), start);
+      std::reverse(result.end() - (leftside-rightside), result.end());
+    }
+  }
+}
+
+auto hash(std::string key) -> std::array<std::uint8_t, 16>;
+auto render(std::array<std::uint8_t, 16> const& hash) -> std::string;
+
+template <std::size_t N, typename It>
+auto hash_ex(std::size_t cycles, It begin, It end)
+ -> std::array<std::uint8_t, N>
+{
+  std::size_t cursor = 0;
+  std::size_t skip = 0;
+  
+  std::array<std::uint8_t, N> result;
+  for (std::size_t i = 0; i < N; i++) { result[i] = i; }
+
+  for (std::size_t i = 0; i < cycles; i++) {
+    std::for_each(begin, end, [&](std::size_t len) {
+      reverser(result, cursor, len);
+      cursor += skip + len;
+      cursor %= N;
+      skip++;
+    });
+  }
+  return result;
+}
+
+} // namespace
+
+#endif