From 1c24e65aa9735e8d775cc3d3fec3324d89c59672 Mon Sep 17 00:00:00 2001
From: Clint Banzhaf <clint@banzhaf.pro>
Date: Sun, 24 Mar 2024 18:38:38 +0100
Subject: [PATCH] Small Improvement on GCD (#77)

---
 include/CppCore.Test/Math/Util.h | 22 ++++++++++--------
 include/CppCore/Math/Util.h      | 39 ++++++++++++++++++++++++--------
 2 files changed, 42 insertions(+), 19 deletions(-)

diff --git a/include/CppCore.Test/Math/Util.h b/include/CppCore.Test/Math/Util.h
index 507c893d..65b61bec 100644
--- a/include/CppCore.Test/Math/Util.h
+++ b/include/CppCore.Test/Math/Util.h
@@ -1448,18 +1448,22 @@ namespace CppCore { namespace Test { namespace Math
 
       INLINE static bool gcd()
       {
+         uint128_t r;
+
+         CppCore::gcd(uint128_t(0),  uint128_t(0),  r); if (r != 0U) return false;
+         CppCore::gcd(uint128_t(1),  uint128_t(0),  r); if (r != 1U) return false;
+         CppCore::gcd(uint128_t(7),  uint128_t(5),  r); if (r != 1U) return false;
+         CppCore::gcd(uint128_t(20), uint128_t(16), r); if (r != 4U) return false;
+         
+         CppCore::gcd(uint128_t(CppCore::Primes::MERSENNE128), uint128_t(CppCore::Primes::LARGE128), r);
+         if (r != 1U) return false;
+
          const uint128_t l1 = uint128_t("2687293461875176346985679234");
          const uint128_t l2 = l1 * 3;
+         CppCore::gcd(l1, l2, r);
+         if (r != l1) return false;
 
-         bool t128 =
-            CppCore::gcd(uint128_t(0), uint128_t(0)) == 0U &&
-            CppCore::gcd(uint128_t(1), uint128_t(0)) == 1U &&
-            CppCore::gcd(uint128_t(7), uint128_t(5)) == 1U &&
-            CppCore::gcd(uint128_t(20), uint128_t(16)) == 4U &&
-            CppCore::gcd(uint128_t(CppCore::Primes::MERSENNE128), uint128_t(CppCore::Primes::LARGE128)) == 1U &&
-            CppCore::gcd(l1, l2) == l1;
-
-         return t128;
+         return true;
       }
    };
 }}}
diff --git a/include/CppCore/Math/Util.h b/include/CppCore/Math/Util.h
index 540f024a..2ba9fc43 100644
--- a/include/CppCore/Math/Util.h
+++ b/include/CppCore/Math/Util.h
@@ -3886,20 +3886,39 @@ namespace CppCore
    /// GCD for any size
    /// </summary>
    template<typename UINT>
-   INLINE static UINT gcd(const UINT& x, const UINT& y)
+   INLINE static void gcd(const UINT& x, const UINT& y, UINT& r)
    {
-      UINT a, b, r;
+      UINT b, t;
       UINT un[2];
+
       if (CppCore::testzero(x))
-         return y;
-      CppCore::clone<UINT>(a, x);
-      CppCore::clone<UINT>(b, y);
-      while (!CppCore::testzero(b))
+         CppCore::clone(r, y);
+
+      else
       {
-         CppCore::umod<UINT, UINT>(r, a, b, un);
-         CppCore::clone<UINT>(a, b);
-         CppCore::clone<UINT>(b, r);
+         CppCore::clone(r, x);
+         CppCore::clone(b, y);
+         while (!CppCore::testzero(b))
+         {
+            CppCore::umod<UINT, UINT>(t, r, b, un);
+            CppCore::clone(r, b);
+            CppCore::clone(b, t);
+         }
       }
-      return a;
+   }
+
+   /// <summary>
+   /// Specialization for uint32_t
+   /// </summary>
+   template<> INLINE static void gcd(const uint32_t& x, const uint32_t& y, uint32_t& r)
+   {
+      r = CppCore::gcd32(x, y);
+   }
+   /// <summary>
+   /// Specialization for uint64_t
+   /// </summary>
+   template<> INLINE static void gcd(const uint64_t& x, const uint64_t& y, uint64_t& r)
+   {
+      r = CppCore::gcd64(x, y);
    }
 }