From 31dea89fe0c7c912cd47003db5340a4c8612835b Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <tim.ledbetter@ladybird.org>
Date: Mon, 14 Apr 2025 10:31:45 +0100
Subject: [PATCH] AK: Add lowest common multiple and greatest common divisor
 functions

---
 AK/IntegralMath.h            | 57 ++++++++++++++++++++++++++++++++++++
 Tests/AK/TestIntegerMath.cpp | 33 +++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/AK/IntegralMath.h b/AK/IntegralMath.h
index ebd279768fa..0f90ae81899 100644
--- a/AK/IntegralMath.h
+++ b/AK/IntegralMath.h
@@ -85,4 +85,61 @@ constexpr T reinterpret_as_octal(T decimal)
     return result;
 }
 
+template<Unsigned T>
+constexpr T gcd(T x, T y)
+{
+    if (x == 0)
+        return y;
+    if (y == 0)
+        return x;
+
+    int shift = 0;
+    while (((x | y) & 1) == 0) {
+        x >>= 1;
+        y >>= 1;
+        shift++;
+    }
+
+    while (x != y) {
+        if (x & 1) {
+            if (y & 1) {
+                if (x > y)
+                    x -= y;
+                else
+                    y -= x;
+            } else {
+                y >>= 1;
+            }
+        } else {
+            x >>= 1;
+            if (y & 1) {
+                if (x < y)
+                    swap(x, y);
+            }
+        }
+    }
+
+    return x << shift;
+}
+
+template<Signed T>
+constexpr T gcd(T x, T y)
+{
+    return gcd(static_cast<MakeUnsigned<T>>(abs(x)), static_cast<MakeUnsigned<T>>(abs(y)));
+}
+
+template<Unsigned T>
+constexpr T lcm(T x, T y)
+{
+    if (x == 0 || y == 0)
+        return 0;
+    return x / gcd(x, y) * y;
+}
+
+template<Signed T>
+constexpr T lcm(T x, T y)
+{
+    return lcm(static_cast<MakeUnsigned<T>>(abs(x)), static_cast<MakeUnsigned<T>>(abs(y)));
+}
+
 }
diff --git a/Tests/AK/TestIntegerMath.cpp b/Tests/AK/TestIntegerMath.cpp
index 26efd83441e..b31ece39ff8 100644
--- a/Tests/AK/TestIntegerMath.cpp
+++ b/Tests/AK/TestIntegerMath.cpp
@@ -131,3 +131,36 @@ TEST_CASE(clamp_to)
     EXPECT_EQ(AK::clamp_to<i64>(-9223372036854775808.0), NumericLimits<i64>::min());
     EXPECT_EQ(AK::clamp_to<i64>(9223372036854775807.0), NumericLimits<i64>::max());
 }
+
+TEST_CASE(gcd)
+{
+    EXPECT_EQ(AK::gcd(0, 0), 0);
+    EXPECT_EQ(AK::gcd(1, 1), 1);
+    EXPECT_EQ(AK::gcd(0, 2), 2);
+    EXPECT_EQ(AK::gcd(2, 0), 2);
+    EXPECT_EQ(AK::gcd(8, 12), 4);
+    EXPECT_EQ(AK::gcd(17, 23), 1);
+    EXPECT_EQ(AK::gcd(48, 36), 12);
+    EXPECT_EQ(AK::gcd(-8, 12), 4);
+    EXPECT_EQ(AK::gcd(8, -12), 4);
+    EXPECT_EQ(AK::gcd(-8, -12), 4);
+    EXPECT_EQ(AK::gcd(100, 100), 100);
+    EXPECT_EQ(AK::gcd(13, 1), 1);
+    EXPECT_EQ(AK::gcd(-NumericLimits<i32>::max(), NumericLimits<i32>::max()), NumericLimits<i32>::max());
+}
+
+TEST_CASE(lcm)
+{
+    EXPECT_EQ(AK::lcm(0, 0), 0);
+    EXPECT_EQ(AK::lcm(0, 5), 0);
+    EXPECT_EQ(AK::lcm(5, 0), 0);
+    EXPECT_EQ(AK::lcm(1, 1), 1);
+    EXPECT_EQ(AK::lcm(4, 6), 12);
+    EXPECT_EQ(AK::lcm(7, 13), 91);
+    EXPECT_EQ(AK::lcm(12, 18), 36);
+    EXPECT_EQ(AK::lcm(-4, 6), 12);
+    EXPECT_EQ(AK::lcm(4, -6), 12);
+    EXPECT_EQ(AK::lcm(-4, -6), 12);
+    EXPECT_EQ(AK::lcm(10, 10), 10);
+    EXPECT_EQ(AK::lcm(1, 8), 8);
+}