From 999a0e200fb7bfe0f72b660fad1d2169afae47b1 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Wed, 2 Dec 2020 13:16:45 -0800
Subject: [PATCH] vm: fix log2 for arm64.

---
 vm/bitwise_hacks.hpp | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/vm/bitwise_hacks.hpp b/vm/bitwise_hacks.hpp
index 5332b8c7b2..ed338dd303 100644
--- a/vm/bitwise_hacks.hpp
+++ b/vm/bitwise_hacks.hpp
@@ -17,24 +17,31 @@ inline cell log2(cell x) {
   asm("bsr %1, %0;" : "=r"(n) : "r"(x));
 #endif
 
+#elif defined(FACTOR_ARM)
+#if defined(_MSC_VER)
+  _BitScanReverse((unsigned long*)&n, x);
+#else
+  n = (31 - __builtin_clz(x));
+#endif
+
 #elif defined(FACTOR_ARM64)
 #if defined(_MSC_VER)
   n = 0;
   _BitScanReverse64((unsigned long*)&n, x);
 #else
-  asm("bsr %1, %0;" : "=r"(n) : "r"(x));
+  n = (63 - __builtin_clzll(x));
 #endif
 
-#elif defined(FACTOR_PPC64)
+#elif defined(FACTOR_PPC32)
 #if defined(__GNUC__)
-  n = (63 - __builtin_clzll(x));
+  n = (31 - __builtin_clz(x));
 #else
 #error Unsupported compiler
 #endif
 
-#elif defined(FACTOR_PPC32)
+#elif defined(FACTOR_PPC64)
 #if defined(__GNUC__)
-  n = (31 - __builtin_clz(x));
+  n = (63 - __builtin_clzll(x));
 #else
 #error Unsupported compiler
 #endif
-- 
2.34.1