/* -*- c++ -*- */
/*
 * Copyright 2013, 2014 Free Software Foundation, Inc.
 *
 * This file is part of VOLK
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

/*!
 * \page volk_32f_invsqrt_32f
 *
 * \b Overview
 *
 * Computes the inverse square root of the input vector and stores
 * result in the output vector.
 *
 * <b>Dispatcher Prototype</b>
 * \code
 * void volk_32f_invsqrt_32f(float* cVector, const float* aVector, unsigned int
 * num_points) \endcode
 *
 * \b Inputs
 * \li aVector: the input vector of floats.
 * \li num_points: The number of data points.
 *
 * \b Outputs
 * \li cVector: The output vector.
 *
 * \b Example
 * \code
 *   int N = 10;
 *   unsigned int alignment = volk_get_alignment();
 *   float* in = (float*)volk_malloc(sizeof(float)*N, alignment);
 *   float* out = (float*)volk_malloc(sizeof(float)*N, alignment);
 *
 *   for(unsigned int ii = 0; ii < N; ++ii){
 *       in[ii] = 1.0 / (float)(ii*ii);
 *   }
 *
 *   volk_32f_invsqrt_32f(out, in, N);
 *
 *   for(unsigned int ii = 0; ii < N; ++ii){
 *       printf("out(%i) = %f\n", ii, out[ii]);
 *   }
 *
 *   volk_free(in);
 *   volk_free(out);
 * \endcode
 */

#ifndef INCLUDED_volk_32f_invsqrt_32f_a_H
#define INCLUDED_volk_32f_invsqrt_32f_a_H

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

static inline float Q_rsqrt(float number)
{
    float x2;
    const float threehalfs = 1.5F;
    union f32_to_i32 {
        int32_t i;
        float f;
    } u;

    x2 = number * 0.5F;
    u.f = number;
    u.i = 0x5f3759df - (u.i >> 1);               // what the fuck?
    u.f = u.f * (threehalfs - (x2 * u.f * u.f)); // 1st iteration
    // u.f  = u.f * ( threehalfs - ( x2 * u.f * u.f ) );   // 2nd iteration, this can be
    // removed

    return u.f;
}

#ifdef LV_HAVE_AVX
#include <immintrin.h>

static inline void
volk_32f_invsqrt_32f_a_avx(float* cVector, const float* aVector, unsigned int num_points)
{
    unsigned int number = 0;
    const unsigned int eighthPoints = num_points / 8;

    float* cPtr = cVector;
    const float* aPtr = aVector;
    __m256 aVal, cVal;
    for (; number < eighthPoints; number++) {
        aVal = _mm256_load_ps(aPtr);
        cVal = _mm256_rsqrt_ps(aVal);
        _mm256_store_ps(cPtr, cVal);
        aPtr += 8;
        cPtr += 8;
    }

    number = eighthPoints * 8;
    for (; number < num_points; number++)
        *cPtr++ = Q_rsqrt(*aPtr++);
}
#endif /* LV_HAVE_AVX */


#ifdef LV_HAVE_SSE
#include <xmmintrin.h>

static inline void
volk_32f_invsqrt_32f_a_sse(float* cVector, const float* aVector, unsigned int num_points)
{
    unsigned int number = 0;
    const unsigned int quarterPoints = num_points / 4;

    float* cPtr = cVector;
    const float* aPtr = aVector;

    __m128 aVal, cVal;
    for (; number < quarterPoints; number++) {

        aVal = _mm_load_ps(aPtr);

        cVal = _mm_rsqrt_ps(aVal);

        _mm_store_ps(cPtr, cVal); // Store the results back into the C container

        aPtr += 4;
        cPtr += 4;
    }

    number = quarterPoints * 4;
    for (; number < num_points; number++) {
        *cPtr++ = Q_rsqrt(*aPtr++);
    }
}
#endif /* LV_HAVE_SSE */


#ifdef LV_HAVE_NEON
#include <arm_neon.h>

static inline void
volk_32f_invsqrt_32f_neon(float* cVector, const float* aVector, unsigned int num_points)
{
    unsigned int number;
    const unsigned int quarter_points = num_points / 4;

    float* cPtr = cVector;
    const float* aPtr = aVector;
    float32x4_t a_val, c_val;
    for (number = 0; number < quarter_points; ++number) {
        a_val = vld1q_f32(aPtr);
        c_val = vrsqrteq_f32(a_val);
        vst1q_f32(cPtr, c_val);
        aPtr += 4;
        cPtr += 4;
    }

    for (number = quarter_points * 4; number < num_points; number++)
        *cPtr++ = Q_rsqrt(*aPtr++);
}
#endif /* LV_HAVE_NEON */


#ifdef LV_HAVE_GENERIC

static inline void volk_32f_invsqrt_32f_generic(float* cVector,
                                                const float* aVector,
                                                unsigned int num_points)
{
    float* cPtr = cVector;
    const float* aPtr = aVector;
    unsigned int number = 0;
    for (number = 0; number < num_points; number++) {
        *cPtr++ = Q_rsqrt(*aPtr++);
    }
}
#endif /* LV_HAVE_GENERIC */

#ifdef LV_HAVE_AVX
#include <immintrin.h>

static inline void
volk_32f_invsqrt_32f_u_avx(float* cVector, const float* aVector, unsigned int num_points)
{
    unsigned int number = 0;
    const unsigned int eighthPoints = num_points / 8;

    float* cPtr = cVector;
    const float* aPtr = aVector;
    __m256 aVal, cVal;
    for (; number < eighthPoints; number++) {
        aVal = _mm256_loadu_ps(aPtr);
        cVal = _mm256_rsqrt_ps(aVal);
        _mm256_storeu_ps(cPtr, cVal);
        aPtr += 8;
        cPtr += 8;
    }

    number = eighthPoints * 8;
    for (; number < num_points; number++)
        *cPtr++ = Q_rsqrt(*aPtr++);
}
#endif /* LV_HAVE_AVX */

#endif /* INCLUDED_volk_32f_invsqrt_32f_a_H */
