/* -*- c++ -*- */
/*
 * Copyright 2012, 2014 Free Software Foundation, Inc.
 *
 * This file is part of VOLK
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

/*!
 * \page volk_64u_popcnt
 *
 * \b Overview
 *
 * Computes the population count (popcnt), or Hamming distance of a
 * binary string. This kernel takes in a single unsigned 64-bit value
 * and returns the count of 1's that the value contains.
 *
 * <b>Dispatcher Prototype</b>
 * \code
 * void volk_64u_popcnt(uint64_t* ret, const uint64_t value)
 * \endcode
 *
 * \b Inputs
 * \li value: The input value.
 *
 * \b Outputs
 * \li ret: The return value containing the popcnt.
 *
 * \b Example
 * \code
 *   int N = 10;
 *   unsigned int alignment = volk_get_alignment();
 *
 *   uint64_t bitstring[] = {0x0, 0x1, 0xf, 0xffffffffffffffff,
 *       0x5555555555555555, 0xaaaaaaaaaaaaaaaa, 0x2a2a2a2a2a2a2a2a,
 *       0xffffffff, 0x32, 0x64};
 *   uint64_t hamming_distance = 0;
 *
 *   for(unsigned int ii=0; ii<N; ++ii){
 *       volk_64u_popcnt(&hamming_distance, bitstring[ii]);
 *       printf("hamming distance of %lx = %li\n", bitstring[ii], hamming_distance);
 *   }
 * \endcode
 */

#ifndef INCLUDED_volk_64u_popcnt_a_H
#define INCLUDED_volk_64u_popcnt_a_H

#include <inttypes.h>
#include <stdio.h>


#ifdef LV_HAVE_GENERIC


static inline void volk_64u_popcnt_generic(uint64_t* ret, const uint64_t value)
{
    // const uint32_t* valueVector = (const uint32_t*)&value;

    // This is faster than a lookup table
    // uint32_t retVal = valueVector[0];
    uint32_t retVal = (uint32_t)(value & 0x00000000FFFFFFFFull);

    retVal = (retVal & 0x55555555) + (retVal >> 1 & 0x55555555);
    retVal = (retVal & 0x33333333) + (retVal >> 2 & 0x33333333);
    retVal = (retVal + (retVal >> 4)) & 0x0F0F0F0F;
    retVal = (retVal + (retVal >> 8));
    retVal = (retVal + (retVal >> 16)) & 0x0000003F;
    uint64_t retVal64 = retVal;

    // retVal = valueVector[1];
    retVal = (uint32_t)((value & 0xFFFFFFFF00000000ull) >> 32);
    retVal = (retVal & 0x55555555) + (retVal >> 1 & 0x55555555);
    retVal = (retVal & 0x33333333) + (retVal >> 2 & 0x33333333);
    retVal = (retVal + (retVal >> 4)) & 0x0F0F0F0F;
    retVal = (retVal + (retVal >> 8));
    retVal = (retVal + (retVal >> 16)) & 0x0000003F;
    retVal64 += retVal;

    *ret = retVal64;
}

#endif /*LV_HAVE_GENERIC*/


#if LV_HAVE_SSE4_2 && LV_HAVE_64

#include <nmmintrin.h>

static inline void volk_64u_popcnt_a_sse4_2(uint64_t* ret, const uint64_t value)
{
    *ret = _mm_popcnt_u64(value);
}

#endif /*LV_HAVE_SSE4_2*/


#if LV_HAVE_NEON
#include <arm_neon.h>
static inline void volk_64u_popcnt_neon(uint64_t* ret, const uint64_t value)
{
    uint8x8_t input_val, count8x8_val;
    uint16x4_t count16x4_val;
    uint32x2_t count32x2_val;
    uint64x1_t count64x1_val;

    input_val = vld1_u8((unsigned char*)&value);
    count8x8_val = vcnt_u8(input_val);
    count16x4_val = vpaddl_u8(count8x8_val);
    count32x2_val = vpaddl_u16(count16x4_val);
    count64x1_val = vpaddl_u32(count32x2_val);
    vst1_u64(ret, count64x1_val);

    //*ret = _mm_popcnt_u64(value);
}
#endif /*LV_HAVE_NEON*/


#endif /*INCLUDED_volk_64u_popcnt_a_H*/
