From 2c4541f735d3dad2ce312bf785c366668d646f3b Mon Sep 17 00:00:00 2001
From: Charles Schlosser <cs.schlosser@gmail.com>
Date: Wed, 13 Dec 2023 03:33:49 +0000
Subject: [PATCH] fix msvc clz

---
 Eigen/src/Core/MathFunctions.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index 087d5db2a..0be29bc9a 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -733,10 +733,9 @@ struct count_bits_impl<BitsType, std::enable_if_t<sizeof(BitsType) <= sizeof(uns
   static constexpr int kNumBits = static_cast<int>(sizeof(BitsType) * CHAR_BIT);
   static_assert(std::is_integral<BitsType>::value, "BitsType must be a built-in integer");
   static EIGEN_DEVICE_FUNC inline int clz(BitsType bits) {
-    static constexpr int kLeadingBitsOffset = static_cast<int>((sizeof(unsigned long) - sizeof(BitsType)) * CHAR_BIT);
     unsigned long out;
     _BitScanReverse(&out, static_cast<unsigned long>(bits));
-    return bits == 0 ? kNumBits : static_cast<int>(out - kLeadingBitsOffset);
+    return bits == 0 ? kNumBits : (kNumBits - 1) - static_cast<int>(out);
   }
 
   static EIGEN_DEVICE_FUNC inline int ctz(BitsType bits) {
@@ -754,10 +753,9 @@ struct count_bits_impl<
   static constexpr int kNumBits = static_cast<int>(sizeof(BitsType) * CHAR_BIT);
   static_assert(std::is_integral<BitsType>::value, "BitsType must be a built-in integer");
   static EIGEN_DEVICE_FUNC inline int clz(BitsType bits) {
-    static constexpr int kLeadingBitsOffset = static_cast<int>((sizeof(__int64) - sizeof(BitsType)) * CHAR_BIT);
     unsigned long out;
     _BitScanReverse64(&out, static_cast<unsigned __int64>(bits));
-    return bits == 0 ? kNumBits : static_cast<int>(out - kLeadingBitsOffset);
+    return bits == 0 ? kNumBits : (kNumBits - 1) - static_cast<int>(out);
   }
 
   static EIGEN_DEVICE_FUNC inline int ctz(BitsType bits) {