/*
//@HEADER
// ************************************************************************
//
//                        Kokkos v. 2.0
//              Copyright (2014) Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
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// Questions? Contact  H. Carter Edwards (hcedwar@sandia.gov)
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*/

#ifndef KOKKOS_BITOPS_HPP
#define KOKKOS_BITOPS_HPP

#include <Kokkos_Macros.hpp>
#include <cstdint>
#include <climits>

namespace Kokkos {
namespace Impl {

/**\brief  Find first zero bit.
 *
 *  If none then return -1 ;
 */
KOKKOS_FORCEINLINE_FUNCTION
int bit_first_zero( unsigned i ) noexcept
{
  enum : unsigned { full = ~0u };

#if defined( __CUDA_ARCH__ )
  return full != i ? __ffs( ~i ) - 1 : -1 ;
#elif defined( __HCC_ACCELERATOR__ )
  return full != i ? (int)hc::__firstbit_u32_u32(~i) : -1 ;
#elif defined( KOKKOS_COMPILER_INTEL )
  return full != i ? _bit_scan_forward( ~i ) : -1 ;
#elif defined( KOKKOS_COMPILER_IBM )
  return full != i ? __cnttz4( ~i ) : -1 ;
#elif defined( KOKKOS_COMPILER_GNU ) || defined( __GNUC__ ) || defined( __GNUG__ )
  return full != i ? __builtin_ffs( ~i ) - 1 : -1 ;
#else
  int offset = -1 ;
  if ( full != i ) {
    for ( offset = 0 ; i & ( 1 << offset ) ; ++offset );
  }
  return offset ;
#endif
}

KOKKOS_FORCEINLINE_FUNCTION
int bit_scan_forward( unsigned i )
{
#if defined( __CUDA_ARCH__ )
  return __ffs(i) - 1;
#elif defined( __HCC_ACCELERATOR__ )
  return  (int)hc::__firstbit_u32_u32(i);
#elif defined( KOKKOS_COMPILER_INTEL )
  return _bit_scan_forward(i);
#elif defined( KOKKOS_COMPILER_IBM )
  return __cnttz4(i);
#elif defined( KOKKOS_COMPILER_GNU ) || defined( __GNUC__ ) || defined( __GNUG__ )
  return __builtin_ffs(i) - 1;
#else
  unsigned t = 1u;
  int r = 0;
  while ( i && ( i & t == 0 ) )
  {
    t = t << 1;
    ++r;
  }
  return r;
#endif
}

KOKKOS_FORCEINLINE_FUNCTION
int bit_scan_reverse( unsigned i )
{
  enum { shift = static_cast<int>( sizeof(unsigned) * CHAR_BIT - 1 ) };
#if defined( __CUDA_ARCH__ )
  return shift - __clz(i);
#elif defined( __HCC_ACCELERATOR__ )
  return  (int)hc::__firstbit_u32_u32(i);
#elif defined( KOKKOS_COMPILER_INTEL )
  return _bit_scan_reverse(i);
#elif defined( KOKKOS_COMPILER_IBM )
  return shift - __cntlz4(i);
#elif defined( __GNUC__ ) || defined( __GNUG__ )
  return shift - __builtin_clz(i);
#else
  unsigned t = 1u << shift;
  int r = 0;
  while ( i && ( i & t == 0 ) )
  {
    t = t >> 1;
    ++r;
  }
  return r;
#endif
}

/// Count the number of bits set.
KOKKOS_FORCEINLINE_FUNCTION
int bit_count( unsigned i )
{
#if defined( __CUDA_ARCH__ )
  return __popc(i);
#elif defined( __HCC_ACCELERATOR__ )
  return  (int)hc::__popcount_u32_b32(i);
#elif defined ( __INTEL_COMPILER )
  return _popcnt32(i);
#elif defined( KOKKOS_COMPILER_IBM )
  return __popcnt4(i);
#elif defined( __GNUC__ ) || defined( __GNUG__ )
  return __builtin_popcount(i);
#else
  // http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetNaive
  i = i - ( ( i >> 1 ) & ~0u / 3u );                             // temp
  i = ( i & ~0u / 15u * 3u ) + ( ( i >> 2 ) & ~0u / 15u * 3u );  // temp
  i = ( i + ( i >> 4 ) ) & ~0u / 255u * 15u;                     // temp

  // count
  return (int)( ( i * ( ~0u / 255u ) ) >> ( sizeof(unsigned) - 1 ) * CHAR_BIT );
#endif
}

KOKKOS_INLINE_FUNCTION
unsigned integral_power_of_two_that_contains( const unsigned N )
{
  const unsigned i = Kokkos::Impl::bit_scan_reverse( N );
  return ( (1u << i) < N ) ? i + 1 : i ;
}


} // namespace Impl
} // namespace Kokkos

#endif // KOKKOS_BITOPS_HPP

