From c903f6b265a3acba2f8c1c99bf11acc2504254d3 Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <github@mhxnet.de>
Date: Fri, 18 Aug 2023 21:49:49 +0200
Subject: [PATCH] Add constexpr rsync_hash::repeating_window()

---
 include/dwarfs/cyclic_hash.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/dwarfs/cyclic_hash.h b/include/dwarfs/cyclic_hash.h
index 559f899f..36c02531 100644
--- a/include/dwarfs/cyclic_hash.h
+++ b/include/dwarfs/cyclic_hash.h
@@ -50,6 +50,13 @@ class rsync_hash {
     len_ = 0;
   }
 
+  static constexpr uint32_t repeating_window(uint8_t byte, size_t length) {
+    uint16_t v = static_cast<uint16_t>(byte);
+    uint16_t a{static_cast<uint16_t>(v * length)};
+    uint16_t b{static_cast<uint16_t>(v * (length * (length + 1)) / 2)};
+    return static_cast<uint32_t>(a) | (static_cast<uint32_t>(b) << 16);
+  }
+
  private:
   uint16_t a_{0};
   uint16_t b_{0};