From 5d333d5af3d60b61a5da36f1df79337a9850d76c Mon Sep 17 00:00:00 2001
From: Ash Vardanian <1983160+ashvardanian@users.noreply.github.com>
Date: Mon, 9 Oct 2023 17:46:27 -0700
Subject: [PATCH] Fix: Missing `__builtin_clzll` symbol

---
 stringzilla/stringzilla.h | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/stringzilla/stringzilla.h b/stringzilla/stringzilla.h
index 94bbde44..cfcd0220 100644
--- a/stringzilla/stringzilla.h
+++ b/stringzilla/stringzilla.h
@@ -806,14 +806,26 @@ inline static void sz_sort_insertion(sz_sequence_t *sequence, sz_sequence_compar
     }
 }
 
-// Utility functions
 inline static sz_size_t _sz_log2i(sz_size_t n) {
-    if (n == 0) return 0;                // to avoid undefined behavior with __builtin_clz
+    if (n == 0) return 0;
+
 #if defined(__LP64__) || defined(_WIN64) // 64-bit
+#ifdef _MSC_VER
+    unsigned long index;
+    _BitScanReverse64(&index, n);
+    return index;
+#else
     return 63 - __builtin_clzll(n);
+#endif
 #else // 32-bit
+#ifdef _MSC_VER
+    unsigned long index;
+    _BitScanReverse(&index, n);
+    return index;
+#else
     return 31 - __builtin_clz(n);
 #endif
+#endif
 }
 
 inline static void _sz_sift_down(