From 84b86b955438a1bbc76e978726a5df1818e284b1 Mon Sep 17 00:00:00 2001
From: Jonathan Giannuzzi <jonathan@giannuzzi.me>
Date: Fri, 10 Oct 2025 15:15:46 +0100
Subject: [PATCH] [C++] Patch vendored pcg library to enable msvc arm64
 intrinsics

This enables building Arrow C++ for Windows ARM64 with MSVC when setting
ARROW_SIMD_LEVEL to NONE (to disable xsimd usage, which does not support
msvc arm64 intrinsics, and is non-trivial to fix).

This patch is based on https://github.com/imneme/pcg-cpp/pull/99.
The upstream pcg library has not been updated in the past 3 years, so
this may never get merged.
---
 cpp/src/arrow/vendored/pcg/README.md       |  1 +
 cpp/src/arrow/vendored/pcg/pcg_uint128.hpp | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/cpp/src/arrow/vendored/pcg/README.md b/cpp/src/arrow/vendored/pcg/README.md
index b58504f3b37..7a949723dad 100644
--- a/cpp/src/arrow/vendored/pcg/README.md
+++ b/cpp/src/arrow/vendored/pcg/README.md
@@ -25,4 +25,5 @@ Sources are taken from git changeset ffd522e7188bef30a00c74dc7eb9de5faff90092
 Changes:
 - enclosed in `arrow_vendored` namespace
 - remove `struct arbitrary_seed` definition because of https://github.com/apache/arrow/issues/35596
+- enable MSVC ARM64 intrinsics to allow building on Windows ARM64 with Visual Studio - see https://github.com/apache/arrow/pull/47779
 
diff --git a/cpp/src/arrow/vendored/pcg/pcg_uint128.hpp b/cpp/src/arrow/vendored/pcg/pcg_uint128.hpp
index 0181e69e4ef..012f3d66823 100644
--- a/cpp/src/arrow/vendored/pcg/pcg_uint128.hpp
+++ b/cpp/src/arrow/vendored/pcg/pcg_uint128.hpp
@@ -67,7 +67,7 @@
         #define PCG_LITTLE_ENDIAN 1
     #elif __BIG_ENDIAN__ || _BIG_ENDIAN
         #define PCG_LITTLE_ENDIAN 0
-    #elif __x86_64 || __x86_64__ || _M_X64 || __i386 || __i386__ || _M_IX86
+    #elif __x86_64 || __x86_64__ || _M_X64 || __i386 || __i386__ || _M_IX86 || _M_ARM64
         #define PCG_LITTLE_ENDIAN 1
     #elif __powerpc__ || __POWERPC__ || __ppc__ || __PPC__ \
           || __m68k__ || __mc68000__
@@ -734,7 +734,13 @@ uint_x4<UInt,UIntX2> operator*(const uint_x4<UInt,UIntX2>& a,
 
 #if PCG_64BIT_SPECIALIZATIONS
 #if defined(_MSC_VER)
+#if defined(_M_X64) || defined(_M_IX86)
 #pragma intrinsic(_umul128)
+#elif defined(_M_ARM64)
+#pragma intrinsic(__umulh)
+#else
+#error Unsupported architecture
+#endif
 #endif
 
 #if defined(_MSC_VER) || __SIZEOF_INT128__
@@ -743,8 +749,15 @@ uint_x4<UInt32,uint64_t> operator*(const uint_x4<UInt32,uint64_t>& a,
 				   const uint_x4<UInt32,uint64_t>& b)
 {
 #if defined(_MSC_VER)
+#if defined(_M_X64) || defined(_M_IX86)
     uint64_t hi;
     uint64_t lo = _umul128(a.d.v01, b.d.v01, &hi);
+#elif defined(_M_ARM64)
+    uint64_t lo = a.d.v01 * b.d.v01;
+    uint64_t hi = __umulh(a.d.v01, b.d.v01);
+#else
+#error Unsupported architecture
+#endif
 #else
     __uint128_t r = __uint128_t(a.d.v01) * __uint128_t(b.d.v01);
     uint64_t lo = uint64_t(r);