libcxx/include/support/win32/support.h

// -*- C++ -*-
//===----------------------- support/win32/support.h ----------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_SUPPORT_WIN32_SUPPORT_H
#define _LIBCPP_SUPPORT_WIN32_SUPPORT_H

/*
   Functions and constants used in libc++ that are missing from the Windows C library.
  */

#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

#ifndef NOMINMAX
#define NOMINMAX
#endif

extern "C" {

int vasprintf( char **sptr, const char *__restrict fmt, va_list ap );
int asprintf( char **sptr, const char *__restrict fmt, ...);
size_t mbsnrtowcs( wchar_t *__restrict dst, const char **__restrict src,
                   size_t nmc, size_t len, mbstate_t *__restrict ps );
size_t wcsnrtombs( char *__restrict dst, const wchar_t **__restrict src,
                   size_t nwc, size_t len, mbstate_t *__restrict ps );
}

#if defined(_LIBCPP_MSVCRT)
#define snprintf _snprintf
#define atoll _atoi64
#define strtoll _strtoi64
#define strtoull _strtoui64
#define wcstoll _wcstoi64
#define wcstoull _wcstoui64
_LIBCPP_ALWAYS_INLINE float strtof( const char *nptr, char **endptr )
{ return _Stof(nptr, endptr, 0); }
_LIBCPP_ALWAYS_INLINE double strtod( const char *nptr, char **endptr )
{ return _Stod(nptr, endptr, 0); }
_LIBCPP_ALWAYS_INLINE long double strtold( const char *nptr, char **endptr )
{ return _Stold(nptr, endptr, 0); }

#define _Exit _exit
#endif

#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...
   static const unsigned int m2 = 0x33333333; //binary: 00110011..
   static const unsigned int m4 = 0x0f0f0f0f; //binary:  4 zeros,  4 ones ...
   static const unsigned int h01= 0x01010101; //the sum of 256 to the power of 0,1,2,3...
   x -= (x >> 1) & m1;             //put count of each 2 bits into those 2 bits
   x = (x & m2) + ((x >> 2) & m2); //put count of each 4 bits into those 4 bits
   x = (x + (x >> 4)) & m4;        //put count of each 8 bits into those 8 bits
   return (x * h01) >> 24;  //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24)
}

_LIBCPP_ALWAYS_INLINE int __builtin_popcountl(unsigned long x) {
  return __builtin_popcount(static_cast<int>(x));
}

_LIBCPP_ALWAYS_INLINE int __builtin_popcountll(unsigned long long x) {
   static const unsigned long long m1  = 0x5555555555555555; //binary: 0101...
   static const unsigned long long m2  = 0x3333333333333333; //binary: 00110011..
   static const unsigned long long m4  = 0x0f0f0f0f0f0f0f0f; //binary:  4 zeros,  4 ones ...
   static const unsigned long long h01 = 0x0101010101010101; //the sum of 256 to the power of 0,1,2,3...
   x -= (x >> 1) & m1;             //put count of each 2 bits into those 2 bits
   x = (x & m2) + ((x >> 2) & m2); //put count of each 4 bits into those 4 bits
   x = (x + (x >> 4)) & m4;        //put count of each 8 bits into those 8 bits
   return static_cast<int>((x * h01)>>56);  //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
}

// 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 )
{
    // Win32 and Win64 expectations.
    static_assert(sizeof(mask)==4,"");
    static_assert(sizeof(unsigned long)==4,"");
    return __builtin_ctzl(static_cast<unsigned long>(mask));
}

// 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_clzl( unsigned long mask )
{
    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 )
{
    return __builtin_clzl(x);
}
#endif // _LIBCPP_MSVC

#endif // _LIBCPP_SUPPORT_WIN32_SUPPORT_H