From 75b80516d5133202b1e6848ad0c6d640543b313c Mon Sep 17 00:00:00 2001
From: Famiu Haque <famiuhaque@proton.me>
Date: Fri, 5 Apr 2024 07:56:35 +0600
Subject: [PATCH] build: fix link error for `_BitScanForward64` (#28173)

Problem: The usage of `_BitScanForward64` causes linking to fail on some systems.
Solution: Correctly check if it exists using `check_c_source_compiles`.
---
 cmake.config/CMakeLists.txt | 11 +++++++++++
 cmake.config/config.h.in    |  1 +
 src/nvim/math.c             |  2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/cmake.config/CMakeLists.txt b/cmake.config/CMakeLists.txt
index f3cc803cf5..d30c522aa2 100644
--- a/cmake.config/CMakeLists.txt
+++ b/cmake.config/CMakeLists.txt
@@ -79,6 +79,17 @@ int main(void)
 }
 " HAVE_PWD_FUNCS)
 
+check_c_source_compiles("
+#include <intrin.h>
+
+int main(void)
+{
+  unsigned long index;
+  unsigned char mask = 0x8000;
+  _BitScanForward64(&index, mask);
+  return 0;
+}
+" HAVE_BITSCANFORWARD64)
 
 if(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
   check_c_source_compiles("
diff --git a/cmake.config/config.h.in b/cmake.config/config.h.in
index 47fbb5bafe..af4e13fc11 100644
--- a/cmake.config/config.h.in
+++ b/cmake.config/config.h.in
@@ -52,3 +52,4 @@
 #cmakedefine HAVE_EXECINFO_BACKTRACE
 #cmakedefine HAVE_BUILTIN_ADD_OVERFLOW
 #cmakedefine HAVE_WIMPLICIT_FALLTHROUGH_FLAG
+#cmakedefine HAVE_BITSCANFORWARD64
diff --git a/src/nvim/math.c b/src/nvim/math.c
index 39d166bb53..2fd9cd6ce7 100644
--- a/src/nvim/math.c
+++ b/src/nvim/math.c
@@ -56,7 +56,7 @@ int xctz(uint64_t x)
   // Use compiler builtin if possible.
 #if defined(__clang__) || (defined(__GNUC__) && (__GNUC__ >= 4))
   return __builtin_ctzll(x);
-#elif defined(_MSC_VER)
+#elif defined(HAVE_BITSCANFORWARD64)
   unsigned long index;
   _BitScanForward64(&index, x);
   return (int)index;