From 8c66d338fc20b2d206c261426a6aed3bcbc6eba2 Mon Sep 17 00:00:00 2001
From: Matthew Parkinson <mattpark@microsoft.com>
Date: Wed, 26 Aug 2020 16:25:57 +0100
Subject: [PATCH] Fixes to ctz on Windows Clang.

---
 src/ds/bits.h              | 30 +++++++++++++++-----------
 src/test/func/bits/bits.cc | 43 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 12 deletions(-)
 create mode 100644 src/test/func/bits/bits.cc

diff --git a/src/ds/bits.h b/src/ds/bits.h
index 50967fd37..a32513aaf 100644
--- a/src/ds/bits.h
+++ b/src/ds/bits.h
@@ -12,9 +12,6 @@
 #include <atomic>
 #include <cstdint>
 #include <type_traits>
-#if defined(_WIN32) && defined(__GNUC__)
-#  define USE_CLZLL
-#endif
 #ifdef pause
 #  undef pause
 #endif
@@ -76,10 +73,15 @@ namespace snmalloc
 
       return BITS - index - 1;
 #  endif
-#elif defined(USE_CLZLL)
-      return static_cast<size_t>(__builtin_clzll(x));
-#else
-      return static_cast<size_t>(__builtin_clzl(x));
+#else 
+      if constexpr (std::is_same_v<unsigned long, std::size_t>)
+      {
+        return __builtin_clzl(x);
+      }
+      else if constexpr (std::is_same_v<unsigned long long, std::size_t>)
+      {
+        return __builtin_clzll(x);
+      }
 #endif
     }
 
@@ -142,17 +144,21 @@ namespace snmalloc
 
     inline size_t ctz(size_t x)
     {
-#if __has_builtin(__builtin_ctzl)
-      return static_cast<size_t>(__builtin_ctzl(x));
-#elif defined(_MSC_VER)
+#if defined(_MSC_VER)
 #  ifdef SNMALLOC_VA_BITS_64
       return _tzcnt_u64(x);
 #  else
       return _tzcnt_u32((uint32_t)x);
 #  endif
 #else
-      // Probably GCC at this point.
-      return static_cast<size_t>(__builtin_ctzl(x));
+      if constexpr (std::is_same_v<unsigned long, std::size_t>)
+      {
+        return __builtin_ctzl(x);
+      }
+      else if constexpr (std::is_same_v<unsigned long long, std::size_t>)
+      {
+        return __builtin_ctzll(x);
+      }
 #endif
     }
 
diff --git a/src/test/func/bits/bits.cc b/src/test/func/bits/bits.cc
new file mode 100644
index 000000000..c521264df
--- /dev/null
+++ b/src/test/func/bits/bits.cc
@@ -0,0 +1,43 @@
+/**
+ * Unit tests for operations in bits.h
+ */
+
+#include <iostream>
+#include <test/setup.h>
+#include <ds/bits.h>
+
+void
+test_ctz()
+{
+  for (size_t i = 0; i < sizeof(size_t) * 8; i++)
+    if (snmalloc::bits::ctz(snmalloc::bits::one_at_bit(i)) != i)
+    {
+      std::cout << "Failed with ctz(one_at_bit(i)) != i for i=" << i << std::endl;
+      abort();
+    }
+}
+
+
+void
+test_clz()
+{
+  const size_t PTRSIZE_LOG = sizeof(size_t) * 8;
+
+  for (size_t i = 0; i < sizeof(size_t) * 8; i++)
+    if (snmalloc::bits::clz(snmalloc::bits::one_at_bit(i)) != (PTRSIZE_LOG - i - 1))
+    {
+      std::cout << "Failed with clz(one_at_bit(i)) != (PTRSIZE_LOG - i - 1) for i=" << i << std::endl;
+      abort();
+    }
+}
+
+int main(int argc, char** argv)
+{
+  UNUSED(argc);
+  UNUSED(argv);
+
+  setup();
+
+  test_clz();
+  test_ctz();
+}
\ No newline at end of file