From 0eff192d47e37fbdb06f0b63726d89dfd4425805 Mon Sep 17 00:00:00 2001
From: Victor Nova <lost@losttech.software>
Date: Thu, 3 Mar 2022 14:07:15 -0800
Subject: [PATCH] support for BigInteger <-> PyInt

fixes https://github.com/pythonnet/pythonnet/issues/1642#issuecomment-1058412759
---
 CHANGELOG.md                     |  1 +
 src/embed_tests/TestConverter.cs | 20 +++++++++++++++
 src/embed_tests/TestPyInt.cs     | 34 ++++++++++++++++++++++++
 src/runtime/Converter.cs         |  8 ++++++
 src/runtime/PythonTypes/PyInt.cs | 44 +++++++++++++++++++++++++++-----
 src/runtime/Runtime.cs           | 16 ++++++++----
 src/runtime/Util/Util.cs         |  7 +++++
 7 files changed, 119 insertions(+), 11 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 382f9ab57..c45a031b2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 -   .NET collection types now implement standard Python collection interfaces from `collections.abc`.
 See [Mixins/collections.py](src/runtime/Mixins/collections.py).
 -   .NET arrays implement Python buffer protocol
+-   Python integer interoperability with `System.Numerics.BigInteger`
 -   Python.NET will correctly resolve .NET methods, that accept `PyList`, `PyInt`,
 and other `PyObject` derived types when called from Python.
 -   .NET classes, that have `__call__` method are callable from Python
diff --git a/src/embed_tests/TestConverter.cs b/src/embed_tests/TestConverter.cs
index 8f7cd381d..e586eda1b 100644
--- a/src/embed_tests/TestConverter.cs
+++ b/src/embed_tests/TestConverter.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Numerics;
 
 using NUnit.Framework;
 
@@ -131,6 +132,25 @@ public void ToNullable()
             Assert.AreEqual(Const, ni);
         }
 
+        [Test]
+        public void BigIntExplicit()
+        {
+            BigInteger val = 42;
+            var i = new PyInt(val);
+            var ni = i.As<BigInteger>();
+            Assert.AreEqual(val, ni);
+            var nullable = i.As<BigInteger?>();
+            Assert.AreEqual(val, nullable);
+        }
+
+        [Test]
+        public void PyIntImplicit()
+        {
+            var i = new PyInt(1);
+            var ni = (PyObject)i.As<object>();
+            Assert.AreEqual(i.rawPtr, ni.rawPtr);
+        }
+
         [Test]
         public void ToPyList()
         {
diff --git a/src/embed_tests/TestPyInt.cs b/src/embed_tests/TestPyInt.cs
index 03a368ed8..822fe0715 100644
--- a/src/embed_tests/TestPyInt.cs
+++ b/src/embed_tests/TestPyInt.cs
@@ -1,4 +1,8 @@
 using System;
+using System.Globalization;
+using System.Linq;
+using System.Numerics;
+
 using NUnit.Framework;
 using Python.Runtime;
 
@@ -179,5 +183,35 @@ public void TestConvertToInt64()
             Assert.IsInstanceOf(typeof(long), a.ToInt64());
             Assert.AreEqual(val, a.ToInt64());
         }
+
+        [Test]
+        public void ToBigInteger()
+        {
+            int[] simpleValues =
+            {
+                0, 1, 2,
+                0x10,
+                0x123,
+                0x1234,
+            };
+            simpleValues = simpleValues.Concat(simpleValues.Select(v => -v)).ToArray();
+
+            foreach (var val in simpleValues)
+            {
+                var pyInt = new PyInt(val);
+                Assert.AreEqual((BigInteger)val, pyInt.ToBigInteger());
+            }
+        }
+
+        [Test]
+        public void ToBigIntegerLarge()
+        {
+            BigInteger val = BigInteger.Pow(2, 1024) + 3;
+            var pyInt = new PyInt(val);
+            Assert.AreEqual(val, pyInt.ToBigInteger());
+            val = -val;
+            pyInt = new PyInt(val);
+            Assert.AreEqual(val, pyInt.ToBigInteger());
+        }
     }
 }
diff --git a/src/runtime/Converter.cs b/src/runtime/Converter.cs
index ff1f01a64..a90f31513 100644
--- a/src/runtime/Converter.cs
+++ b/src/runtime/Converter.cs
@@ -455,6 +455,14 @@ internal static bool ToManagedValue(BorrowedReference value, Type obType,
                 }
             }
 
+            if (obType == typeof(System.Numerics.BigInteger)
+                && Runtime.PyInt_Check(value))
+            {
+                using var pyInt = new PyInt(value);
+                result = pyInt.ToBigInteger();
+                return true;
+            }
+
             return ToPrimitive(value, obType, out result, setError);
         }
 
diff --git a/src/runtime/PythonTypes/PyInt.cs b/src/runtime/PythonTypes/PyInt.cs
index d503c15f3..3dcc6ddb2 100644
--- a/src/runtime/PythonTypes/PyInt.cs
+++ b/src/runtime/PythonTypes/PyInt.cs
@@ -1,21 +1,21 @@
 using System;
+using System.Globalization;
+using System.Numerics;
 using System.Runtime.Serialization;
 
 namespace Python.Runtime
 {
     /// <summary>
-    /// Represents a Python integer object. See the documentation at
-    /// PY2: https://docs.python.org/2/c-api/int.html
-    /// PY3: No equivalent
-    /// for details.
+    /// Represents a Python integer object.
+    /// See the documentation at https://docs.python.org/3/c-api/long.html
     /// </summary>
-    public class PyInt : PyNumber
+    public class PyInt : PyNumber, IFormattable
     {
         internal PyInt(in StolenReference ptr) : base(ptr)
         {
         }
 
-        internal PyInt(BorrowedReference reference): base(reference)
+        internal PyInt(BorrowedReference reference) : base(reference)
         {
             if (!Runtime.PyInt_Check(reference)) throw new ArgumentException("object is not an int");
         }
@@ -135,6 +135,8 @@ public PyInt(string value) : base(Runtime.PyLong_FromString(value, 0).StealOrThr
         {
         }
 
+        public PyInt(BigInteger value) : this(value.ToString(CultureInfo.InvariantCulture)) { }
+
         protected PyInt(SerializationInfo info, StreamingContext context)
             : base(info, context) { }
 
@@ -198,5 +200,35 @@ public long ToInt64()
             }
             return val.Value;
         }
+
+        public BigInteger ToBigInteger()
+        {
+            using var pyHex = Runtime.HexCallable.Invoke(this);
+            string hex = pyHex.As<string>();
+            int offset = 0;
+            bool neg = false;
+            if (hex[0] == '-')
+            {
+                offset++;
+                neg = true;
+            }
+            byte[] littleEndianBytes = new byte[(hex.Length - offset + 1) / 2];
+            for (; offset < hex.Length; offset++)
+            {
+                int littleEndianHexIndex = hex.Length - 1 - offset;
+                int byteIndex = littleEndianHexIndex / 2;
+                int isByteTopHalf = littleEndianHexIndex & 1;
+                int valueShift = isByteTopHalf * 4;
+                littleEndianBytes[byteIndex] += (byte)(Util.HexToInt(hex[offset]) << valueShift);
+            }
+            var result = new BigInteger(littleEndianBytes);
+            return neg ? -result : result;
+        }
+
+        public string ToString(string format, IFormatProvider formatProvider)
+        {
+            using var _ = Py.GIL();
+            return ToBigInteger().ToString(format, formatProvider);
+        }
     }
 }
diff --git a/src/runtime/Runtime.cs b/src/runtime/Runtime.cs
index e33c4624c..b48ba92e3 100644
--- a/src/runtime/Runtime.cs
+++ b/src/runtime/Runtime.cs
@@ -179,6 +179,7 @@ internal static void Initialize(bool initSigs = false)
 
             clrInterop = GetModuleLazy("clr.interop");
             inspect = GetModuleLazy("inspect");
+            hexCallable = new(() => new PyString("%x").GetAttr("__mod__"));
         }
 
         static void NewRun()
@@ -279,8 +280,9 @@ internal static void Shutdown()
 
             Exceptions.Shutdown();
             PythonEngine.InteropConfiguration.Dispose();
-            DisposeLazyModule(clrInterop);
-            DisposeLazyModule(inspect);
+            DisposeLazyObject(clrInterop);
+            DisposeLazyObject(inspect);
+            DisposeLazyObject(hexCallable);
             PyObjectConversions.Reset();
 
             PyGC_Collect();
@@ -352,11 +354,11 @@ static bool TryCollectingGarbage(int runs, bool forceBreakLoops)
         public static bool TryCollectingGarbage(int runs)
             => TryCollectingGarbage(runs, forceBreakLoops: false);
 
-        static void DisposeLazyModule(Lazy<PyObject> module)
+        static void DisposeLazyObject(Lazy<PyObject> pyObject)
         {
-            if (module.IsValueCreated)
+            if (pyObject.IsValueCreated)
             {
-                module.Value.Dispose();
+                pyObject.Value.Dispose();
             }
         }
 
@@ -489,8 +491,12 @@ private static void NullGCHandles(IEnumerable<IntPtr> objects)
 
         private static Lazy<PyObject> inspect;
         internal static PyObject InspectModule => inspect.Value;
+
         private static Lazy<PyObject> clrInterop;
         internal static PyObject InteropModule => clrInterop.Value;
+
+        private static Lazy<PyObject> hexCallable;
+        internal static PyObject HexCallable => hexCallable.Value;
 #pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
 
         internal static BorrowedReference CLRMetaType => PyCLRMetaType;
diff --git a/src/runtime/Util/Util.cs b/src/runtime/Util/Util.cs
index f5f0d2957..89f5bdf4c 100644
--- a/src/runtime/Util/Util.cs
+++ b/src/runtime/Util/Util.cs
@@ -141,6 +141,13 @@ internal static string ReadStringResource(this System.Reflection.Assembly assemb
             return reader.ReadToEnd();
         }
 
+        public static int HexToInt(char hex) => hex switch
+        {
+            >= '0' and <= '9' => hex - '0',
+            >= 'a' and <= 'f' => hex - 'a' + 10,
+            _ => throw new ArgumentOutOfRangeException(nameof(hex)),
+        };
+
         public static IEnumerator<T> GetEnumerator<T>(this IEnumerator<T> enumerator) => enumerator;
 
         public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source)

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