[libcxx] r198481 - Implement the functions: clz, clzl, clzll, ctz, ctzl, and ctzll
Yaron Keren
yaron.keren at gmail.com
Sat Jan 4 00:56:00 PST 2014
Author: yrnkrn
Date: Sat Jan 4 02:56:00 2014
New Revision: 198481
URL: http://llvm.org/viewvc/llvm-project?rev=198481&view=rev
Log:
Implement the functions: clz, clzl, clzll, ctz, ctzl, and ctzll
for libcxx when compiled with Visual C++ on Win32 and Win64.
clang and gcc (MinGW) compilers provide these implementations themselves.
Modified:
libcxx/trunk/include/support/win32/support.h
Modified: libcxx/trunk/include/support/win32/support.h
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/support/win32/support.h?rev=198481&r1=198480&r2=198481&view=diff
==============================================================================
--- libcxx/trunk/include/support/win32/support.h (original)
+++ libcxx/trunk/include/support/win32/support.h Sat Jan 4 02:56:00 2014
@@ -17,6 +17,14 @@
#include <wchar.h> // mbstate_t
#include <cstdarg> // va_ macros
+// "builtins" not implemented here for Clang or GCC as they provide implementations.
+// Assuming required for elsewhere else, certainly MSVC.
+#if defined(_LIBCPP_MSVC)
+#include <intrin.h>
+#endif
+#if defined(_LIBCPP_MSVCRT)
+#include <xlocinfo.h>
+#endif
#define swprintf _snwprintf
#define vswprintf _vsnwprintf
@@ -36,7 +44,6 @@ size_t wcsnrtombs( char *__restrict dst,
#if defined(_LIBCPP_MSVCRT)
#define snprintf _snprintf
-#include <xlocinfo.h>
#define atoll _atoi64
#define strtoll _strtoi64
#define strtoull _strtoui64
@@ -50,9 +57,15 @@ _LIBCPP_ALWAYS_INLINE long double strtol
{ return _Stold(nptr, endptr, 0); }
#define _Exit _exit
+#endif
-#ifndef __clang__ // MSVC-based Clang also defines _MSC_VER
-#include <intrin.h>
+#if defined(_LIBCPP_MSVC)
+
+// Bit builtin's make these assumptions when calling _BitScanForward/Reverse etc.
+// These assumptions are expected to be true for Win32/Win64 which this file supports.
+static_assert(sizeof(unsigned long long)==8,"");
+static_assert(sizeof(unsigned long)==4,"");
+static_assert(sizeof(unsigned int)==4,"");
_LIBCPP_ALWAYS_INLINE int __builtin_popcount(unsigned int x) {
static const unsigned int m1 = 0x55555555; //binary: 0101...
@@ -80,39 +93,87 @@ _LIBCPP_ALWAYS_INLINE int __builtin_popc
return static_cast<int>((x * h01)>>56); //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
}
-_LIBCPP_ALWAYS_INLINE int __builtin_ctz( unsigned int x )
+// Returns the number of trailing 0-bits in x,
+// starting at the least significant bit position.
+// If x is 0, the result is undefined.
+_LIBCPP_ALWAYS_INLINE int __builtin_ctzll( unsigned long long mask )
+{
+ unsigned long where;
+ // Search from LSB to MSB for first set bit.
+ // Returns zero if no set bit is found.
+#if defined(_WIN64)
+ if (_BitScanForward64(&where, mask))
+ return static_cast<int>(where);
+#elif defined(_WIN32)
+ // Win32 doesn't have _BitScanForward64 so emulate it with two 32 bit calls.
+ // Scan the Low Word
+ if (_BitScanForward(&where, static_cast<unsigned long>(mask)))
+ return static_cast<int>(where);
+ // Scan the High Word
+ if (_BitScanForward(&where, static_cast<unsigned long>(mask >> 32)))
+ return static_cast<int>(where+32); // Create a bit offset from the LSB.
+#else
+# error "Implementation of __builtin_ctzll required"
+#endif
+ return 64;
+}
+
+_LIBCPP_ALWAYS_INLINE int __builtin_ctzl( unsigned long mask )
+{
+ unsigned long where;
+ // Search from LSB to MSB for first set bit.
+ // Returns zero if no set bit is found.
+ if (_BitScanForward(&where, mask))
+ return static_cast<int>(where);
+ return 32;
+}
+
+_LIBCPP_ALWAYS_INLINE int __builtin_ctz( unsigned int mask )
{
- DWORD r = 0;
- _BitScanReverse(&r, x);
- return static_cast<int>(r);
+ // Win32 and Win64 expectations.
+ static_assert(sizeof(mask)==4,"");
+ static_assert(sizeof(unsigned long)==4,"");
+ return __builtin_ctzl(static_cast<unsigned long>(mask));
}
-// sizeof(long) == sizeof(int) on Windows
-_LIBCPP_ALWAYS_INLINE int __builtin_ctzl( unsigned long x )
-{ return __builtin_ctz( static_cast<int>(x) ); }
+// Returns the number of leading 0-bits in x,
+// starting at the most significant bit position.
+// If x is 0, the result is undefined.
+_LIBCPP_ALWAYS_INLINE int __builtin_clzll( unsigned long long mask )
+{
+ unsigned long where;
+ // BitScanReverse scans from MSB to LSB for first set bit.
+ // Returns 0 if no set bit is found.
+#if defined(_WIN64)
+ if (_BitScanReverse64(&where, mask))
+ return static_cast<int>(63-where);
+#elif defined(_WIN32)
+ // Scan the high 32 bits.
+ if (_BitScanReverse(&where, static_cast<unsigned long>(mask >> 32)))
+ return static_cast<int>(63-(where+32)); // Create a bit offset from the MSB.
+ // Scan the low 32 bits.
+ if (_BitScanReverse(&where, static_cast<unsigned long>(mask)))
+ return static_cast<int>(63-where);
+#else
+# error "Implementation of __builtin_clzll required"
+#endif
+ return 64; // Undefined Behavior.
+}
-_LIBCPP_ALWAYS_INLINE int __builtin_ctzll( unsigned long long x )
+_LIBCPP_ALWAYS_INLINE int __builtin_clzl( unsigned long mask )
{
- DWORD r = 0;
- _BitScanReverse64(&r, x);
- return static_cast<int>(r);
+ unsigned long where;
+ // Search from LSB to MSB for first set bit.
+ // Returns zero if no set bit is found.
+ if (_BitScanReverse(&where, mask))
+ return static_cast<int>(31-where);
+ return 32; // Undefined Behavior.
}
+
_LIBCPP_ALWAYS_INLINE int __builtin_clz( unsigned int x )
{
- DWORD r = 0;
- _BitScanForward(&r, x);
- return static_cast<int>(r);
-}
-// sizeof(long) == sizeof(int) on Windows
-_LIBCPP_ALWAYS_INLINE int __builtin_clzl( unsigned long x )
-{ return __builtin_clz( static_cast<int>(x) ); }
-_LIBCPP_ALWAYS_INLINE int __builtin_clzll( unsigned long long x )
-{
- DWORD r = 0;
- _BitScanForward64(&r, x);
- return static_cast<int>(r);
+ return __builtin_clzl(x);
}
-#endif // !__clang__
-#endif // _LIBCPP_MSVCRT
+#endif // _LIBCPP_MSVC
#endif // _LIBCPP_SUPPORT_WIN32_SUPPORT_H
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