added Verlet scheme and NxN non-bonded functionality

[gromacs.git] / include / gmx_math_x86_sse4_1_single.h

/* -*- mode: c; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; c-file-style: "stroustrup"; -*-
 *
 * 
 * This file is part of GROMACS.
 * Copyright (c) 2012-  
 *
 * Written by the Gromacs development team under coordination of
 * David van der Spoel, Berk Hess, and Erik Lindahl.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * To help us fund GROMACS development, we humbly ask that you cite
 * the research papers on the package. Check out http://www.gromacs.org
 * 
 * And Hey:
 * Gnomes, ROck Monsters And Chili Sauce
 */
#ifndef _gmx_math_x86_sse4_1_single_h_
#define _gmx_math_x86_sse4_1_single_h_

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

#include "gmx_x86_sse4_1.h"



#ifndef M_PI
#  define M_PI 3.14159265358979323846264338327950288
#endif




/************************
 *                      *
 * Simple math routines *
 *                      *
 ************************/

/* 1.0/sqrt(x) */
static gmx_inline __m128
gmx_mm_invsqrt_ps(__m128 x)
{
    const __m128 half  = _mm_set_ps(0.5,0.5,0.5,0.5);
    const __m128 three = _mm_set_ps(3.0,3.0,3.0,3.0);

    __m128 lu = _mm_rsqrt_ps(x);

    return _mm_mul_ps(half,_mm_mul_ps(_mm_sub_ps(three,_mm_mul_ps(_mm_mul_ps(lu,lu),x)),lu));
}

/* sqrt(x) - Do NOT use this (but rather invsqrt) if you actually need 1.0/sqrt(x) */
static gmx_inline __m128
gmx_mm_sqrt_ps(__m128 x)
{
    __m128 mask;
    __m128 res;

    mask = _mm_cmpeq_ps(x,_mm_setzero_ps());
    res  = _mm_andnot_ps(mask,gmx_mm_invsqrt_ps(x));

    res  = _mm_mul_ps(x,res);

    return res;
}

/* 1.0/x */
static gmx_inline __m128
gmx_mm_inv_ps(__m128 x)
{
    const __m128 two = _mm_set_ps(2.0f,2.0f,2.0f,2.0f);

    __m128 lu = _mm_rcp_ps(x);

    return _mm_mul_ps(lu,_mm_sub_ps(two,_mm_mul_ps(lu,x)));
}

static gmx_inline __m128
gmx_mm_abs_ps(__m128 x)
{
    const __m128 signmask  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x7FFFFFFF) );

    return _mm_and_ps(x,signmask);
}



static __m128
gmx_mm_log_ps(__m128 x)
{
    /* Same algorithm as cephes library */
    const __m128  expmask    = gmx_mm_castsi128_ps( _mm_set_epi32(0x7F800000, 0x7F800000, 0x7F800000, 0x7F800000) );
    const __m128i expbase_m1 = _mm_set1_epi32(127-1); /* We want non-IEEE format */
    const __m128  half       = _mm_set1_ps(0.5f);
    const __m128  one        = _mm_set1_ps(1.0f);
    const __m128  invsq2     = _mm_set1_ps(1.0f/sqrt(2.0f));
    const __m128  corr1      = _mm_set1_ps(-2.12194440e-4f);
    const __m128  corr2      = _mm_set1_ps(0.693359375f);

    const __m128 CA_1        = _mm_set1_ps(0.070376836292f);
    const __m128 CB_0        = _mm_set1_ps(1.6714950086782716f);
    const __m128 CB_1        = _mm_set1_ps(-2.452088066061482f);
    const __m128 CC_0        = _mm_set1_ps(1.5220770854701728f);
    const __m128 CC_1        = _mm_set1_ps(-1.3422238433233642f);
    const __m128 CD_0        = _mm_set1_ps(1.386218787509749f);
    const __m128 CD_1        = _mm_set1_ps(0.35075468953796346f);
    const __m128 CE_0        = _mm_set1_ps(1.3429983063133937f);
    const __m128 CE_1        = _mm_set1_ps(1.807420826584643f);

    __m128  fexp,fexp1;
    __m128i iexp;
    __m128  mask;
    __m128  x1,x2;
    __m128  y;
    __m128  pA,pB,pC,pD,pE,tB,tC,tD,tE;

    /* Separate x into exponent and mantissa, with a mantissa in the range [0.5..1[ (not IEEE754 standard!) */
    fexp  = _mm_and_ps(x,expmask);
    iexp  = gmx_mm_castps_si128(fexp);
    iexp  = _mm_srli_epi32(iexp,23);
    iexp  = _mm_sub_epi32(iexp,expbase_m1);

    x     = _mm_andnot_ps(expmask,x);
    x     = _mm_or_ps(x,one);
    x     = _mm_mul_ps(x,half);

    mask  = _mm_cmplt_ps(x,invsq2);

    x     = _mm_add_ps(x,_mm_and_ps(mask,x));
    x     = _mm_sub_ps(x,one);
    iexp  = _mm_add_epi32(iexp,gmx_mm_castps_si128(mask)); /* 0xFFFFFFFF = -1 as int */

    x2    = _mm_mul_ps(x,x);

    pA    = _mm_mul_ps(CA_1,x);
    pB    = _mm_mul_ps(CB_1,x);
    pC    = _mm_mul_ps(CC_1,x);
    pD    = _mm_mul_ps(CD_1,x);
    pE    = _mm_mul_ps(CE_1,x);
    tB    = _mm_add_ps(CB_0,x2);
    tC    = _mm_add_ps(CC_0,x2);
    tD    = _mm_add_ps(CD_0,x2);
    tE    = _mm_add_ps(CE_0,x2);
    pB    = _mm_add_ps(pB,tB);
    pC    = _mm_add_ps(pC,tC);
    pD    = _mm_add_ps(pD,tD);
    pE    = _mm_add_ps(pE,tE);

    pA    = _mm_mul_ps(pA,pB);
    pC    = _mm_mul_ps(pC,pD);
    pE    = _mm_mul_ps(pE,x2);
    pA    = _mm_mul_ps(pA,pC);
    y     = _mm_mul_ps(pA,pE);

    fexp  = _mm_cvtepi32_ps(iexp);
    y     = _mm_add_ps(y,_mm_mul_ps(fexp,corr1));

    y     = _mm_sub_ps(y, _mm_mul_ps(half,x2));
    x2    = _mm_add_ps(x,y);

    x2    = _mm_add_ps(x2,_mm_mul_ps(fexp,corr2));

    return x2;
}


/*
 * 2^x function.
 *
 * The 2^w term is calculated from a (6,0)-th order (no denominator) Minimax polynomia on the interval
 * [-0.5,0.5]. The coefficiencts of this was derived in Mathematica using the command:
 *
 * MiniMaxApproximation[(2^x), {x, {-0.5, 0.5}, 6, 0}, WorkingPrecision -> 15]
 *
 * The largest-magnitude exponent we can represent in IEEE single-precision binary format
 * is 2^-126 for small numbers and 2^127 for large ones. To avoid wrap-around problems, we set the
 * result to zero if the argument falls outside this range. For small numbers this is just fine, but
 * for large numbers you could be fancy and return the smallest/largest IEEE single-precision
 * number instead. That would take a few extra cycles and not really help, since something is
 * wrong if you are using single precision to work with numbers that cannot really be represented
 * in single precision.
 *
 * The accuracy is at least 23 bits.
 */
static __m128
gmx_mm_exp2_ps(__m128 x)
{
    /* Lower bound: We do not allow numbers that would lead to an IEEE fp representation exponent smaller than -126. */
    const __m128  arglimit = _mm_set1_ps(126.0f);

    const __m128i expbase  = _mm_set1_epi32(127);
    const __m128  CA6      = _mm_set1_ps(1.535336188319500E-004);
    const __m128  CA5      = _mm_set1_ps(1.339887440266574E-003);
    const __m128  CA4      = _mm_set1_ps(9.618437357674640E-003);
    const __m128  CA3      = _mm_set1_ps(5.550332471162809E-002);
    const __m128  CA2      = _mm_set1_ps(2.402264791363012E-001);
    const __m128  CA1      = _mm_set1_ps(6.931472028550421E-001);
    const __m128  CA0      = _mm_set1_ps(1.0f);

    __m128  valuemask;
    __m128i iexppart;
    __m128  fexppart;
    __m128  intpart;
    __m128  x2;
    __m128  p0,p1;

    iexppart  = _mm_cvtps_epi32(x);
    intpart   = _mm_round_ps(x,_MM_FROUND_TO_NEAREST_INT);
    iexppart  = _mm_slli_epi32(_mm_add_epi32(iexppart,expbase),23);
    valuemask = _mm_cmpge_ps(arglimit,gmx_mm_abs_ps(x));
    fexppart  = _mm_and_ps(valuemask,gmx_mm_castsi128_ps(iexppart));

    x         = _mm_sub_ps(x,intpart);
    x2        = _mm_mul_ps(x,x);

    p0        = _mm_mul_ps(CA6,x2);
    p1        = _mm_mul_ps(CA5,x2);
    p0        = _mm_add_ps(p0,CA4);
    p1        = _mm_add_ps(p1,CA3);
    p0        = _mm_mul_ps(p0,x2);
    p1        = _mm_mul_ps(p1,x2);
    p0        = _mm_add_ps(p0,CA2);
    p1        = _mm_add_ps(p1,CA1);
    p0        = _mm_mul_ps(p0,x2);
    p1        = _mm_mul_ps(p1,x);
    p0        = _mm_add_ps(p0,CA0);
    p0        = _mm_add_ps(p0,p1);
    x         = _mm_mul_ps(p0,fexppart);

    return  x;
}


/* Exponential function. This could be calculated from 2^x as Exp(x)=2^(y), where y=log2(e)*x,
 * but there will then be a small rounding error since we lose some precision due to the
 * multiplication. This will then be magnified a lot by the exponential.
 *
 * Instead, we calculate the fractional part directly as a minimax approximation of
 * Exp(z) on [-0.5,0.5]. We use extended precision arithmetics to calculate the fraction
 * remaining after 2^y, which avoids the precision-loss.
 * The final result is correct to within 1 LSB over the entire argument range.
 */
static __m128
gmx_mm_exp_ps(__m128 x)
{
    const __m128  argscale      = _mm_set1_ps(1.44269504088896341f);
    /* Lower bound: Disallow numbers that would lead to an IEEE fp exponent reaching +-127. */
    const __m128  arglimit      = _mm_set1_ps(126.0f);
    const __m128i expbase       = _mm_set1_epi32(127);

    const __m128  invargscale0  = _mm_set1_ps(0.693359375f);
    const __m128  invargscale1  = _mm_set1_ps(-2.12194440e-4f);

    const __m128  CC5           = _mm_set1_ps(1.9875691500e-4f);
    const __m128  CC4           = _mm_set1_ps(1.3981999507e-3f);
    const __m128  CC3           = _mm_set1_ps(8.3334519073e-3f);
    const __m128  CC2           = _mm_set1_ps(4.1665795894e-2f);
    const __m128  CC1           = _mm_set1_ps(1.6666665459e-1f);
    const __m128  CC0           = _mm_set1_ps(5.0000001201e-1f);
    const __m128  one           = _mm_set1_ps(1.0f);

    __m128  y,x2;
    __m128  p0,p1;
    __m128  valuemask;
    __m128i iexppart;
    __m128  fexppart;
    __m128  intpart;

    y = _mm_mul_ps(x,argscale);

    iexppart  = _mm_cvtps_epi32(y);
    intpart   = _mm_round_ps(y,_MM_FROUND_TO_NEAREST_INT);

    iexppart  = _mm_slli_epi32(_mm_add_epi32(iexppart,expbase),23);
    valuemask = _mm_cmpge_ps(arglimit,gmx_mm_abs_ps(y));
    fexppart  = _mm_and_ps(valuemask,gmx_mm_castsi128_ps(iexppart));

    /* Extended precision arithmetics */
    x         = _mm_sub_ps(x,_mm_mul_ps(invargscale0,intpart));
    x         = _mm_sub_ps(x,_mm_mul_ps(invargscale1,intpart));

    x2        = _mm_mul_ps(x,x);

    p1        = _mm_mul_ps(CC5,x2);
    p0        = _mm_mul_ps(CC4,x2);
    p1        = _mm_add_ps(p1,CC3);
    p0        = _mm_add_ps(p0,CC2);
    p1        = _mm_mul_ps(p1,x2);
    p0        = _mm_mul_ps(p0,x2);
    p1        = _mm_add_ps(p1,CC1);
    p0        = _mm_add_ps(p0,CC0);
    p1        = _mm_mul_ps(p1,x);
    p0        = _mm_add_ps(p0,p1);
    p0        = _mm_mul_ps(p0,x2);
    x         = _mm_add_ps(x,one);
    x         = _mm_add_ps(x,p0);

    x         = _mm_mul_ps(x,fexppart);

    return x;
}

/* FULL precision. Only errors in LSB */
static __m128
gmx_mm_erf_ps(__m128 x)
{
    /* Coefficients for minimax approximation of erf(x)=x*P(x^2) in range [-1,1] */
    const __m128  CA6      = _mm_set1_ps(7.853861353153693e-5f);
    const __m128  CA5      = _mm_set1_ps(-8.010193625184903e-4f);
    const __m128  CA4      = _mm_set1_ps(5.188327685732524e-3f);
    const __m128  CA3      = _mm_set1_ps(-2.685381193529856e-2f);
    const __m128  CA2      = _mm_set1_ps(1.128358514861418e-1f);
    const __m128  CA1      = _mm_set1_ps(-3.761262582423300e-1f);
    const __m128  CA0      = _mm_set1_ps(1.128379165726710f);
    /* Coefficients for minimax approximation of erfc(x)=Exp(-x^2)*P((1/(x-1))^2) in range [0.67,2] */
    const __m128  CB9      = _mm_set1_ps(-0.0018629930017603923f);
    const __m128  CB8      = _mm_set1_ps(0.003909821287598495f);
    const __m128  CB7      = _mm_set1_ps(-0.0052094582210355615f);
    const __m128  CB6      = _mm_set1_ps(0.005685614362160572f);
    const __m128  CB5      = _mm_set1_ps(-0.0025367682853477272f);
    const __m128  CB4      = _mm_set1_ps(-0.010199799682318782f);
    const __m128  CB3      = _mm_set1_ps(0.04369575504816542f);
    const __m128  CB2      = _mm_set1_ps(-0.11884063474674492f);
    const __m128  CB1      = _mm_set1_ps(0.2732120154030589f);
    const __m128  CB0      = _mm_set1_ps(0.42758357702025784f);
    /* Coefficients for minimax approximation of erfc(x)=Exp(-x^2)*(1/x)*P((1/x)^2) in range [2,9.19] */
    const __m128  CC10     = _mm_set1_ps(-0.0445555913112064f);
    const __m128  CC9      = _mm_set1_ps(0.21376355144663348f);
    const __m128  CC8      = _mm_set1_ps(-0.3473187200259257f);
    const __m128  CC7      = _mm_set1_ps(0.016690861551248114f);
    const __m128  CC6      = _mm_set1_ps(0.7560973182491192f);
    const __m128  CC5      = _mm_set1_ps(-1.2137903600145787f);
    const __m128  CC4      = _mm_set1_ps(0.8411872321232948f);
    const __m128  CC3      = _mm_set1_ps(-0.08670413896296343f);
    const __m128  CC2      = _mm_set1_ps(-0.27124782687240334f);
    const __m128  CC1      = _mm_set1_ps(-0.0007502488047806069f);
    const __m128  CC0      = _mm_set1_ps(0.5642114853803148f);

    /* Coefficients for expansion of exp(x) in [0,0.1] */
    /* CD0 and CD1 are both 1.0, so no need to declare them separately */
    const __m128  CD2      = _mm_set1_ps(0.5000066608081202f);
    const __m128  CD3      = _mm_set1_ps(0.1664795422874624f);
    const __m128  CD4      = _mm_set1_ps(0.04379839977652482f);

    const __m128  sieve    = gmx_mm_castsi128_ps( _mm_set1_epi32(0xfffff000) );
    const __m128  signbit  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x80000000) );
    const __m128  one      = _mm_set1_ps(1.0f);
    const __m128  two      = _mm_set1_ps(2.0f);

    __m128 x2,x4,y;
    __m128 z,q,t,t2,w,w2;
    __m128 pA0,pA1,pB0,pB1,pC0,pC1;
    __m128 expmx2,corr;
    __m128 res_erf,res_erfc,res;
    __m128 mask;

    /* Calculate erf() */
    x2     = _mm_mul_ps(x,x);
    x4     = _mm_mul_ps(x2,x2);

    pA0  = _mm_mul_ps(CA6,x4);
    pA1  = _mm_mul_ps(CA5,x4);
    pA0  = _mm_add_ps(pA0,CA4);
    pA1  = _mm_add_ps(pA1,CA3);
    pA0  = _mm_mul_ps(pA0,x4);
    pA1  = _mm_mul_ps(pA1,x4);
    pA0  = _mm_add_ps(pA0,CA2);
    pA1  = _mm_add_ps(pA1,CA1);
    pA0  = _mm_mul_ps(pA0,x4);
    pA1  = _mm_mul_ps(pA1,x2);
    pA0  = _mm_add_ps(pA0,pA1);
    pA0  = _mm_add_ps(pA0,CA0);

    res_erf = _mm_mul_ps(x,pA0);

    /* Calculate erfc */

    y       = gmx_mm_abs_ps(x);
    t       = gmx_mm_inv_ps(y);
    w       = _mm_sub_ps(t,one);
    t2      = _mm_mul_ps(t,t);
    w2      = _mm_mul_ps(w,w);
    /*
     * We cannot simply calculate exp(-x2) directly in single precision, since
     * that will lose a couple of bits of precision due to the multiplication.
     * Instead, we introduce x=z+w, where the last 12 bits of precision are in w.
     * Then we get exp(-x2) = exp(-z2)*exp((z-x)*(z+x)).
     *
     * The only drawback with this is that it requires TWO separate exponential
     * evaluations, which would be horrible performance-wise. However, the argument
     * for the second exp() call is always small, so there we simply use a
     * low-order minimax expansion on [0,0.1].
     */

    z       = _mm_and_ps(y,sieve);
    q       = _mm_mul_ps( _mm_sub_ps(z,y) , _mm_add_ps(z,y) );

    corr    = _mm_mul_ps(CD4,q);
    corr    = _mm_add_ps(corr,CD3);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,CD2);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,one);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,one);

    expmx2  = gmx_mm_exp_ps( _mm_or_ps( signbit , _mm_mul_ps(z,z) ) );
    expmx2  = _mm_mul_ps(expmx2,corr);

    pB1  = _mm_mul_ps(CB9,w2);
    pB0  = _mm_mul_ps(CB8,w2);
    pB1  = _mm_add_ps(pB1,CB7);
    pB0  = _mm_add_ps(pB0,CB6);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB5);
    pB0  = _mm_add_ps(pB0,CB4);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB3);
    pB0  = _mm_add_ps(pB0,CB2);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB1);
    pB1  = _mm_mul_ps(pB1,w);
    pB0  = _mm_add_ps(pB0,pB1);
    pB0  = _mm_add_ps(pB0,CB0);

    pC0  = _mm_mul_ps(CC10,t2);
    pC1  = _mm_mul_ps(CC9,t2);
    pC0  = _mm_add_ps(pC0,CC8);
    pC1  = _mm_add_ps(pC1,CC7);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC6);
    pC1  = _mm_add_ps(pC1,CC5);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC4);
    pC1  = _mm_add_ps(pC1,CC3);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC2);
    pC1  = _mm_add_ps(pC1,CC1);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t);
    pC0  = _mm_add_ps(pC0,pC1);
    pC0  = _mm_add_ps(pC0,CC0);
    pC0  = _mm_mul_ps(pC0,t);

    /* SELECT pB0 or pC0 for erfc() */
    mask = _mm_cmplt_ps(two,y);
    res_erfc = _mm_blendv_ps(pB0,pC0,mask);
    res_erfc = _mm_mul_ps(res_erfc,expmx2);

    /* erfc(x<0) = 2-erfc(|x|) */
    mask = _mm_cmplt_ps(x,_mm_setzero_ps());
    res_erfc = _mm_blendv_ps(res_erfc,_mm_sub_ps(two,res_erfc),mask);

    /* Select erf() or erfc() */
    mask = _mm_cmplt_ps(y,_mm_set1_ps(0.75f));
    res  = _mm_blendv_ps(_mm_sub_ps(one,res_erfc),res_erf,mask);

    return res;
}


/* FULL precision. Only errors in LSB */
static __m128
gmx_mm_erfc_ps(__m128 x)
{
    /* Coefficients for minimax approximation of erf(x)=x*P(x^2) in range [-1,1] */
    const __m128  CA6      = _mm_set1_ps(7.853861353153693e-5f);
    const __m128  CA5      = _mm_set1_ps(-8.010193625184903e-4f);
    const __m128  CA4      = _mm_set1_ps(5.188327685732524e-3f);
    const __m128  CA3      = _mm_set1_ps(-2.685381193529856e-2f);
    const __m128  CA2      = _mm_set1_ps(1.128358514861418e-1f);
    const __m128  CA1      = _mm_set1_ps(-3.761262582423300e-1f);
    const __m128  CA0      = _mm_set1_ps(1.128379165726710f);
    /* Coefficients for minimax approximation of erfc(x)=Exp(-x^2)*P((1/(x-1))^2) in range [0.67,2] */
    const __m128  CB9      = _mm_set1_ps(-0.0018629930017603923f);
    const __m128  CB8      = _mm_set1_ps(0.003909821287598495f);
    const __m128  CB7      = _mm_set1_ps(-0.0052094582210355615f);
    const __m128  CB6      = _mm_set1_ps(0.005685614362160572f);
    const __m128  CB5      = _mm_set1_ps(-0.0025367682853477272f);
    const __m128  CB4      = _mm_set1_ps(-0.010199799682318782f);
    const __m128  CB3      = _mm_set1_ps(0.04369575504816542f);
    const __m128  CB2      = _mm_set1_ps(-0.11884063474674492f);
    const __m128  CB1      = _mm_set1_ps(0.2732120154030589f);
    const __m128  CB0      = _mm_set1_ps(0.42758357702025784f);
    /* Coefficients for minimax approximation of erfc(x)=Exp(-x^2)*(1/x)*P((1/x)^2) in range [2,9.19] */
    const __m128  CC10     = _mm_set1_ps(-0.0445555913112064f);
    const __m128  CC9      = _mm_set1_ps(0.21376355144663348f);
    const __m128  CC8      = _mm_set1_ps(-0.3473187200259257f);
    const __m128  CC7      = _mm_set1_ps(0.016690861551248114f);
    const __m128  CC6      = _mm_set1_ps(0.7560973182491192f);
    const __m128  CC5      = _mm_set1_ps(-1.2137903600145787f);
    const __m128  CC4      = _mm_set1_ps(0.8411872321232948f);
    const __m128  CC3      = _mm_set1_ps(-0.08670413896296343f);
    const __m128  CC2      = _mm_set1_ps(-0.27124782687240334f);
    const __m128  CC1      = _mm_set1_ps(-0.0007502488047806069f);
    const __m128  CC0      = _mm_set1_ps(0.5642114853803148f);

    /* Coefficients for expansion of exp(x) in [0,0.1] */
    /* CD0 and CD1 are both 1.0, so no need to declare them separately */
    const __m128  CD2      = _mm_set1_ps(0.5000066608081202f);
    const __m128  CD3      = _mm_set1_ps(0.1664795422874624f);
    const __m128  CD4      = _mm_set1_ps(0.04379839977652482f);

    const __m128  sieve    = gmx_mm_castsi128_ps( _mm_set1_epi32(0xfffff000) );
    const __m128  signbit  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x80000000) );
    const __m128  one      = _mm_set1_ps(1.0f);
    const __m128  two      = _mm_set1_ps(2.0f);

    __m128 x2,x4,y;
    __m128 z,q,t,t2,w,w2;
    __m128 pA0,pA1,pB0,pB1,pC0,pC1;
    __m128 expmx2,corr;
    __m128 res_erf,res_erfc,res;
    __m128 mask;

    /* Calculate erf() */
    x2     = _mm_mul_ps(x,x);
    x4     = _mm_mul_ps(x2,x2);

    pA0  = _mm_mul_ps(CA6,x4);
    pA1  = _mm_mul_ps(CA5,x4);
    pA0  = _mm_add_ps(pA0,CA4);
    pA1  = _mm_add_ps(pA1,CA3);
    pA0  = _mm_mul_ps(pA0,x4);
    pA1  = _mm_mul_ps(pA1,x4);
    pA0  = _mm_add_ps(pA0,CA2);
    pA1  = _mm_add_ps(pA1,CA1);
    pA0  = _mm_mul_ps(pA0,x4);
    pA1  = _mm_mul_ps(pA1,x2);
    pA0  = _mm_add_ps(pA0,pA1);
    pA0  = _mm_add_ps(pA0,CA0);

    res_erf = _mm_mul_ps(x,pA0);

    /* Calculate erfc */
    y       = gmx_mm_abs_ps(x);
    t       = gmx_mm_inv_ps(y);
    w       = _mm_sub_ps(t,one);
    t2      = _mm_mul_ps(t,t);
    w2      = _mm_mul_ps(w,w);
    /*
     * We cannot simply calculate exp(-x2) directly in single precision, since
     * that will lose a couple of bits of precision due to the multiplication.
     * Instead, we introduce x=z+w, where the last 12 bits of precision are in w.
     * Then we get exp(-x2) = exp(-z2)*exp((z-x)*(z+x)).
     *
     * The only drawback with this is that it requires TWO separate exponential
     * evaluations, which would be horrible performance-wise. However, the argument
     * for the second exp() call is always small, so there we simply use a
     * low-order minimax expansion on [0,0.1].
     */

    z       = _mm_and_ps(y,sieve);
    q       = _mm_mul_ps( _mm_sub_ps(z,y) , _mm_add_ps(z,y) );

    corr    = _mm_mul_ps(CD4,q);
    corr    = _mm_add_ps(corr,CD3);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,CD2);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,one);
    corr    = _mm_mul_ps(corr,q);
    corr    = _mm_add_ps(corr,one);

    expmx2  = gmx_mm_exp_ps( _mm_or_ps( signbit , _mm_mul_ps(z,z) ) );
    expmx2  = _mm_mul_ps(expmx2,corr);

    pB1  = _mm_mul_ps(CB9,w2);
    pB0  = _mm_mul_ps(CB8,w2);
    pB1  = _mm_add_ps(pB1,CB7);
    pB0  = _mm_add_ps(pB0,CB6);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB5);
    pB0  = _mm_add_ps(pB0,CB4);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB3);
    pB0  = _mm_add_ps(pB0,CB2);
    pB1  = _mm_mul_ps(pB1,w2);
    pB0  = _mm_mul_ps(pB0,w2);
    pB1  = _mm_add_ps(pB1,CB1);
    pB1  = _mm_mul_ps(pB1,w);
    pB0  = _mm_add_ps(pB0,pB1);
    pB0  = _mm_add_ps(pB0,CB0);

    pC0  = _mm_mul_ps(CC10,t2);
    pC1  = _mm_mul_ps(CC9,t2);
    pC0  = _mm_add_ps(pC0,CC8);
    pC1  = _mm_add_ps(pC1,CC7);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC6);
    pC1  = _mm_add_ps(pC1,CC5);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC4);
    pC1  = _mm_add_ps(pC1,CC3);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t2);
    pC0  = _mm_add_ps(pC0,CC2);
    pC1  = _mm_add_ps(pC1,CC1);
    pC0  = _mm_mul_ps(pC0,t2);
    pC1  = _mm_mul_ps(pC1,t);
    pC0  = _mm_add_ps(pC0,pC1);
    pC0  = _mm_add_ps(pC0,CC0);
    pC0  = _mm_mul_ps(pC0,t);

    /* SELECT pB0 or pC0 for erfc() */
    mask = _mm_cmplt_ps(two,y);
    res_erfc = _mm_blendv_ps(pB0,pC0,mask);
    res_erfc = _mm_mul_ps(res_erfc,expmx2);

    /* erfc(x<0) = 2-erfc(|x|) */
    mask = _mm_cmplt_ps(x,_mm_setzero_ps());
    res_erfc = _mm_blendv_ps(res_erfc,_mm_sub_ps(two,res_erfc),mask);

    /* Select erf() or erfc() */
    mask = _mm_cmplt_ps(y,_mm_set1_ps(0.75f));
    res  = _mm_blendv_ps(res_erfc,_mm_sub_ps(one,res_erf),mask);

    return res;
}


/* Calculate the force correction due to PME analytically.
 *
 * This routine is meant to enable analytical evaluation of the
 * direct-space PME electrostatic force to avoid tables. 
 *
 * The direct-space potential should be Erfc(beta*r)/r, but there
 * are some problems evaluating that: 
 *
 * First, the error function is difficult (read: expensive) to 
 * approxmiate accurately for intermediate to large arguments, and
 * this happens already in ranges of beta*r that occur in simulations.
 * Second, we now try to avoid calculating potentials in Gromacs but
 * use forces directly.
 *
 * We can simply things slight by noting that the PME part is really
 * a correction to the normal Coulomb force since Erfc(z)=1-Erf(z), i.e.
 *
 * V= 1/r - Erf(beta*r)/r
 *
 * The first term we already have from the inverse square root, so
 * that we can leave out of this routine. 
 *
 * For pme tolerances of 1e-3 to 1e-8 and cutoffs of 0.5nm to 1.8nm,
 * the argument beta*r will be in the range 0.15 to ~4. Use your 
 * favorite plotting program to realize how well-behaved Erf(z)/z is
 * in this range! 
 *
 * We approximate f(z)=erf(z)/z with a rational minimax polynomial. 
 * However, it turns out it is more efficient to approximate f(z)/z and
 * then only use even powers. This is another minor optimization, since
 * we actually WANT f(z)/z, because it is going to be multiplied by
 * the vector between the two atoms to get the vectorial force. The 
 * fastest flops are the ones we can avoid calculating!
 * 
 * So, here's how it should be used:
 *
 * 1. Calculate r^2.
 * 2. Multiply by beta^2, so you get z^2=beta^2*r^2.
 * 3. Evaluate this routine with z^2 as the argument.
 * 4. The return value is the expression:
 *
 *  
 *       2*exp(-z^2)     erf(z)
 *       ------------ - --------
 *       sqrt(Pi)*z^2      z^3
 * 
 * 5. Multiply the entire expression by beta^3. This will get you
 *
 *       beta^3*2*exp(-z^2)     beta^3*erf(z)
 *       ------------------  - ---------------
 *          sqrt(Pi)*z^2            z^3
 * 
 *    or, switching back to r (z=r*beta):
 *
 *       2*beta*exp(-r^2*beta^2)   erf(r*beta)
 *       ----------------------- - -----------
 *            sqrt(Pi)*r^2            r^3
 *
 *
 *    With a bit of math exercise you should be able to confirm that
 *    this is exactly D[Erf[beta*r]/r,r] divided by r another time.
 *
 * 6. Add the result to 1/r^3, multiply by the product of the charges,
 *    and you have your force (divided by r). A final multiplication
 *    with the vector connecting the two particles and you have your
 *    vectorial force to add to the particles.
 *
 */
static gmx_inline __m128
gmx_mm_pmecorrF_ps(__m128 z2)
{
    const __m128  FN6      = _mm_set1_ps(-1.7357322914161492954e-8f);
    const __m128  FN5      = _mm_set1_ps(1.4703624142580877519e-6f);
    const __m128  FN4      = _mm_set1_ps(-0.000053401640219807709149f);
    const __m128  FN3      = _mm_set1_ps(0.0010054721316683106153f);
    const __m128  FN2      = _mm_set1_ps(-0.019278317264888380590f);
    const __m128  FN1      = _mm_set1_ps(0.069670166153766424023f);
    const __m128  FN0      = _mm_set1_ps(-0.75225204789749321333f);
    
    const __m128  FD4      = _mm_set1_ps(0.0011193462567257629232f);
    const __m128  FD3      = _mm_set1_ps(0.014866955030185295499f);
    const __m128  FD2      = _mm_set1_ps(0.11583842382862377919f);
    const __m128  FD1      = _mm_set1_ps(0.50736591960530292870f);
    const __m128  FD0      = _mm_set1_ps(1.0f);
    
    __m128 z4;
    __m128 polyFN0,polyFN1,polyFD0,polyFD1;
    
    z4             = _mm_mul_ps(z2,z2);
    
    polyFD0        = _mm_mul_ps(FD4,z4);
    polyFD1        = _mm_mul_ps(FD3,z4);
    polyFD0        = _mm_add_ps(polyFD0,FD2);
    polyFD1        = _mm_add_ps(polyFD1,FD1);
    polyFD0        = _mm_mul_ps(polyFD0,z4);
    polyFD1        = _mm_mul_ps(polyFD1,z2);
    polyFD0        = _mm_add_ps(polyFD0,FD0);
    polyFD0        = _mm_add_ps(polyFD0,polyFD1);
    
    polyFD0        = gmx_mm_inv_ps(polyFD0);
    
    polyFN0        = _mm_mul_ps(FN6,z4);
    polyFN1        = _mm_mul_ps(FN5,z4);
    polyFN0        = _mm_add_ps(polyFN0,FN4);
    polyFN1        = _mm_add_ps(polyFN1,FN3);
    polyFN0        = _mm_mul_ps(polyFN0,z4);
    polyFN1        = _mm_mul_ps(polyFN1,z4);
    polyFN0        = _mm_add_ps(polyFN0,FN2);
    polyFN1        = _mm_add_ps(polyFN1,FN1);
    polyFN0        = _mm_mul_ps(polyFN0,z4);
    polyFN1        = _mm_mul_ps(polyFN1,z2);
    polyFN0        = _mm_add_ps(polyFN0,FN0);
    polyFN0        = _mm_add_ps(polyFN0,polyFN1);
    
    return   _mm_mul_ps(polyFN0,polyFD0);
}


/* Calculate the potential correction due to PME analytically.
 *
 * See gmx_mm256_pmecorrF_ps() for details about the approximation.
 *
 * This routine calculates Erf(z)/z, although you should provide z^2
 * as the input argument.
 *
 * Here's how it should be used:
 *
 * 1. Calculate r^2.
 * 2. Multiply by beta^2, so you get z^2=beta^2*r^2.
 * 3. Evaluate this routine with z^2 as the argument.
 * 4. The return value is the expression:
 *
 *  
 *        erf(z)
 *       --------
 *          z
 * 
 * 5. Multiply the entire expression by beta and switching back to r (z=r*beta):
 *
 *       erf(r*beta)
 *       -----------
 *           r 
 *
 * 6. Add the result to 1/r, multiply by the product of the charges,
 *    and you have your potential.
 */
static gmx_inline __m128
gmx_mm_pmecorrV_ps(__m128 z2)
{
    const __m128  VN6      = _mm_set1_ps(1.9296833005951166339e-8f);
    const __m128  VN5      = _mm_set1_ps(-1.4213390571557850962e-6f);
    const __m128  VN4      = _mm_set1_ps(0.000041603292906656984871f);
    const __m128  VN3      = _mm_set1_ps(-0.00013134036773265025626f);
    const __m128  VN2      = _mm_set1_ps(0.038657983986041781264f);
    const __m128  VN1      = _mm_set1_ps(0.11285044772717598220f);
    const __m128  VN0      = _mm_set1_ps(1.1283802385263030286f);
    
    const __m128  VD3      = _mm_set1_ps(0.0066752224023576045451f);
    const __m128  VD2      = _mm_set1_ps(0.078647795836373922256f);
    const __m128  VD1      = _mm_set1_ps(0.43336185284710920150f);
    const __m128  VD0      = _mm_set1_ps(1.0f);
    
    __m128 z4;
    __m128 polyVN0,polyVN1,polyVD0,polyVD1;
    
    z4             = _mm_mul_ps(z2,z2);
    
    polyVD1        = _mm_mul_ps(VD3,z4);
    polyVD0        = _mm_mul_ps(VD2,z4);
    polyVD1        = _mm_add_ps(polyVD1,VD1);
    polyVD0        = _mm_add_ps(polyVD0,VD0);
    polyVD1        = _mm_mul_ps(polyVD1,z2);
    polyVD0        = _mm_add_ps(polyVD0,polyVD1);
    
    polyVD0        = gmx_mm_inv_ps(polyVD0);
    
    polyVN0        = _mm_mul_ps(VN6,z4);
    polyVN1        = _mm_mul_ps(VN5,z4);
    polyVN0        = _mm_add_ps(polyVN0,VN4);
    polyVN1        = _mm_add_ps(polyVN1,VN3);
    polyVN0        = _mm_mul_ps(polyVN0,z4);
    polyVN1        = _mm_mul_ps(polyVN1,z4);
    polyVN0        = _mm_add_ps(polyVN0,VN2);
    polyVN1        = _mm_add_ps(polyVN1,VN1);
    polyVN0        = _mm_mul_ps(polyVN0,z4);
    polyVN1        = _mm_mul_ps(polyVN1,z2);
    polyVN0        = _mm_add_ps(polyVN0,VN0);
    polyVN0        = _mm_add_ps(polyVN0,polyVN1);
    
    return   _mm_mul_ps(polyVN0,polyVD0);
}


static int
gmx_mm_sincos_ps(__m128 x,
                 __m128 *sinval,
                 __m128 *cosval)
{
    const __m128 two_over_pi = _mm_set1_ps(2.0/M_PI);
    const __m128 half        = _mm_set1_ps(0.5);
    const __m128 one         = _mm_set1_ps(1.0);

    const __m128i izero      = _mm_set1_epi32(0);
    const __m128i ione       = _mm_set1_epi32(1);
    const __m128i itwo       = _mm_set1_epi32(2);
    const __m128i ithree     = _mm_set1_epi32(3);
    const __m128  signbit    = gmx_mm_castsi128_ps( _mm_set1_epi32(0x80000000) );

    const __m128 CA1         = _mm_set1_ps(1.5703125f);
    const __m128 CA2         = _mm_set1_ps(4.837512969970703125e-4f);
    const __m128 CA3         = _mm_set1_ps(7.54978995489188216e-8f);

    const __m128 CC0         = _mm_set1_ps(-0.0013602249f);
    const __m128 CC1         = _mm_set1_ps(0.0416566950f);
    const __m128 CC2         = _mm_set1_ps(-0.4999990225f);
    const __m128 CS0         = _mm_set1_ps(-0.0001950727f);
    const __m128 CS1         = _mm_set1_ps(0.0083320758f);
    const __m128 CS2         = _mm_set1_ps(-0.1666665247f);

    __m128  y,y2;
    __m128  z;
    __m128i iz;
    __m128i offset_sin,offset_cos;
    __m128  tmp1,tmp2;
    __m128  mask_sin,mask_cos;
    __m128  tmp_sin,tmp_cos;

    y          = _mm_mul_ps(x,two_over_pi);
    y          = _mm_add_ps(y,_mm_or_ps(_mm_and_ps(y,signbit),half));

    iz         = _mm_cvttps_epi32(y);
    z          = _mm_round_ps(y,_MM_FROUND_TO_ZERO);

    offset_sin = _mm_and_si128(iz,ithree);
    offset_cos = _mm_add_epi32(iz,ione);

    /* Extended precision arithmethic to achieve full precision */
    y               = _mm_mul_ps(z,CA1);
    tmp1            = _mm_mul_ps(z,CA2);
    tmp2            = _mm_mul_ps(z,CA3);
    y               = _mm_sub_ps(x,y);
    y               = _mm_sub_ps(y,tmp1);
    y               = _mm_sub_ps(y,tmp2);

    y2              = _mm_mul_ps(y,y);

    tmp1            = _mm_mul_ps(CC0,y2);
    tmp1            = _mm_add_ps(tmp1,CC1);
    tmp2            = _mm_mul_ps(CS0,y2);
    tmp2            = _mm_add_ps(tmp2,CS1);
    tmp1            = _mm_mul_ps(tmp1,y2);
    tmp1            = _mm_add_ps(tmp1,CC2);
    tmp2            = _mm_mul_ps(tmp2,y2);
    tmp2            = _mm_add_ps(tmp2,CS2);

    tmp1            = _mm_mul_ps(tmp1,y2);
    tmp1            = _mm_add_ps(tmp1,one);

    tmp2            = _mm_mul_ps(tmp2,_mm_mul_ps(y,y2));
    tmp2            = _mm_add_ps(tmp2,y);

    mask_sin        = gmx_mm_castsi128_ps(_mm_cmpeq_epi32( _mm_and_si128(offset_sin,ione), izero));
    mask_cos        = gmx_mm_castsi128_ps(_mm_cmpeq_epi32( _mm_and_si128(offset_cos,ione), izero));

    tmp_sin         = _mm_blendv_ps(tmp1,tmp2,mask_sin);
    tmp_cos         = _mm_blendv_ps(tmp1,tmp2,mask_cos);

    mask_sin        = gmx_mm_castsi128_ps(_mm_cmpeq_epi32( _mm_and_si128(offset_sin,itwo), izero));
    mask_cos        = gmx_mm_castsi128_ps(_mm_cmpeq_epi32( _mm_and_si128(offset_cos,itwo), izero));

    tmp1            = _mm_xor_ps(signbit,tmp_sin);
    tmp2            = _mm_xor_ps(signbit,tmp_cos);

    *sinval         = _mm_blendv_ps(tmp1,tmp_sin,mask_sin);
    *cosval         = _mm_blendv_ps(tmp2,tmp_cos,mask_cos);

    return 0;
}

/*
 * IMPORTANT: Do NOT call both sin & cos if you need both results, since each of them
 * will then call the sincos() routine and waste a factor 2 in performance!
 */
static __m128
gmx_mm_sin_ps(__m128 x)
{
    __m128 s,c;
    gmx_mm_sincos_ps(x,&s,&c);
    return s;
}

/*
 * IMPORTANT: Do NOT call both sin & cos if you need both results, since each of them
 * will then call the sincos() routine and waste a factor 2 in performance!
 */
static __m128
gmx_mm_cos_ps(__m128 x)
{
    __m128 s,c;
    gmx_mm_sincos_ps(x,&s,&c);
    return c;
}


static __m128
gmx_mm_tan_ps(__m128 x)
{
    __m128 sinval,cosval;
    __m128 tanval;

    gmx_mm_sincos_ps(x,&sinval,&cosval);

    tanval = _mm_mul_ps(sinval,gmx_mm_inv_ps(cosval));

    return tanval;
}


static __m128
gmx_mm_asin_ps(__m128 x)
{
    /* Same algorithm as cephes library */
    const __m128 signmask  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x7FFFFFFF) );
    const __m128 limitlow  = _mm_set1_ps(1e-4f);
    const __m128 half      = _mm_set1_ps(0.5f);
    const __m128 one       = _mm_set1_ps(1.0f);
    const __m128 halfpi    = _mm_set1_ps(M_PI/2.0f);

    const __m128 CC5        = _mm_set1_ps(4.2163199048E-2f);
    const __m128 CC4        = _mm_set1_ps(2.4181311049E-2f);
    const __m128 CC3        = _mm_set1_ps(4.5470025998E-2f);
    const __m128 CC2        = _mm_set1_ps(7.4953002686E-2f);
    const __m128 CC1        = _mm_set1_ps(1.6666752422E-1f);

    __m128 sign;
    __m128 mask;
    __m128 xabs;
    __m128 z,z1,z2,q,q1,q2;
    __m128 pA,pB;

    sign  = _mm_andnot_ps(signmask,x);
    xabs  = _mm_and_ps(x,signmask);

    mask  = _mm_cmpgt_ps(xabs,half);

    z1    = _mm_mul_ps(half, _mm_sub_ps(one,xabs));
    q1    = _mm_mul_ps(z1,gmx_mm_invsqrt_ps(z1));
    q1    = _mm_andnot_ps(_mm_cmpeq_ps(xabs,one),q1);

    q2    = xabs;
    z2    = _mm_mul_ps(q2,q2);

    z     = _mm_or_ps( _mm_and_ps(mask,z1) , _mm_andnot_ps(mask,z2) );
    q     = _mm_or_ps( _mm_and_ps(mask,q1) , _mm_andnot_ps(mask,q2) );

    z2    = _mm_mul_ps(z,z);

    pA    = _mm_mul_ps(CC5,z2);
    pB    = _mm_mul_ps(CC4,z2);

    pA    = _mm_add_ps(pA,CC3);
    pB    = _mm_add_ps(pB,CC2);

    pA    = _mm_mul_ps(pA,z2);
    pB    = _mm_mul_ps(pB,z2);

    pA    = _mm_add_ps(pA,CC1);
    pA    = _mm_mul_ps(pA,z);

    z     = _mm_add_ps(pA,pB);
    z     = _mm_mul_ps(z,q);
    z     = _mm_add_ps(z,q);

    q2    = _mm_sub_ps(halfpi,z);
    q2    = _mm_sub_ps(q2,z);

    z     = _mm_or_ps( _mm_and_ps(mask,q2) , _mm_andnot_ps(mask,z) );

    mask  = _mm_cmpgt_ps(xabs,limitlow);
    z     = _mm_or_ps( _mm_and_ps(mask,z) , _mm_andnot_ps(mask,xabs) );

    z = _mm_xor_ps(z,sign);

    return z;
}


static __m128
gmx_mm_acos_ps(__m128 x)
{
    const __m128 signmask  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x7FFFFFFF) );
    const __m128 one_ps    = _mm_set1_ps(1.0f);
    const __m128 half_ps   = _mm_set1_ps(0.5f);
    const __m128 pi_ps     = _mm_set1_ps(M_PI);
    const __m128 halfpi_ps = _mm_set1_ps(M_PI/2.0f);

    __m128 mask1;
    __m128 mask2;
    __m128 xabs;
    __m128 z,z1,z2,z3;

    xabs  = _mm_and_ps(x,signmask);
    mask1 = _mm_cmpgt_ps(xabs,half_ps);
    mask2 = _mm_cmpgt_ps(x,_mm_setzero_ps());

    z     = _mm_mul_ps(half_ps,_mm_sub_ps(one_ps,xabs));
    z     = _mm_mul_ps(z,gmx_mm_invsqrt_ps(z));
    z     = _mm_andnot_ps(_mm_cmpeq_ps(xabs,one_ps),z);

    z     = _mm_blendv_ps(x,z,mask1);
    z     = gmx_mm_asin_ps(z);

    z2    = _mm_add_ps(z,z);
    z1    = _mm_sub_ps(pi_ps,z2);
    z3    = _mm_sub_ps(halfpi_ps,z);

    z     = _mm_blendv_ps(z1,z2,mask2);
    z     = _mm_blendv_ps(z3,z,mask1);

    return z;
}


static __m128
gmx_mm_atan_ps(__m128 x)
{
    /* Same algorithm as cephes library */
    const __m128 signmask  = gmx_mm_castsi128_ps( _mm_set1_epi32(0x7FFFFFFF) );
    const __m128 limit1    = _mm_set1_ps(0.414213562373095f);
    const __m128 limit2    = _mm_set1_ps(2.414213562373095f);
    const __m128 quarterpi = _mm_set1_ps(0.785398163397448f);
    const __m128 halfpi    = _mm_set1_ps(1.570796326794896f);
    const __m128 mone      = _mm_set1_ps(-1.0f);
    const __m128 CC3       = _mm_set1_ps(-3.33329491539E-1f);
    const __m128 CC5       = _mm_set1_ps(1.99777106478E-1f);
    const __m128 CC7       = _mm_set1_ps(-1.38776856032E-1);
    const __m128 CC9       = _mm_set1_ps(8.05374449538e-2f);

    __m128 sign;
    __m128 mask1,mask2;
    __m128 y,z1,z2;
    __m128 x2,x4;
    __m128 sum1,sum2;

    sign  = _mm_andnot_ps(signmask,x);
    x     = _mm_and_ps(x,signmask);

    mask1 = _mm_cmpgt_ps(x,limit1);
    mask2 = _mm_cmpgt_ps(x,limit2);

    z1    = _mm_mul_ps(_mm_add_ps(x,mone),gmx_mm_inv_ps(_mm_sub_ps(x,mone)));
    z2    = _mm_mul_ps(mone,gmx_mm_inv_ps(x));

    y     = _mm_and_ps(mask1,quarterpi);
    y     = _mm_blendv_ps(y,halfpi,mask2);

    x     = _mm_blendv_ps(x,z1,mask1);
    x     = _mm_blendv_ps(x,z2,mask2);

    x2    = _mm_mul_ps(x,x);
    x4    = _mm_mul_ps(x2,x2);

    sum1  = _mm_mul_ps(CC9,x4);
    sum2  = _mm_mul_ps(CC7,x4);
    sum1  = _mm_add_ps(sum1,CC5);
    sum2  = _mm_add_ps(sum2,CC3);
    sum1  = _mm_mul_ps(sum1,x4);
    sum2  = _mm_mul_ps(sum2,x2);

    sum1  = _mm_add_ps(sum1,sum2);
    sum1  = _mm_sub_ps(sum1,mone);
    sum1  = _mm_mul_ps(sum1,x);
    y     = _mm_add_ps(y,sum1);

    y     = _mm_xor_ps(y,sign);

    return y;
}


static __m128
gmx_mm_atan2_ps(__m128 y, __m128 x)
{
    const __m128 pi          = _mm_set1_ps(M_PI);
    const __m128 minuspi     = _mm_set1_ps(-M_PI);
    const __m128 halfpi      = _mm_set1_ps(M_PI/2.0);
    const __m128 minushalfpi = _mm_set1_ps(-M_PI/2.0);

    __m128 z,z1,z3,z4;
    __m128 w;
    __m128 maskx_lt,maskx_eq;
    __m128 masky_lt,masky_eq;
    __m128 mask1,mask2,mask3,mask4,maskall;

    maskx_lt  = _mm_cmplt_ps(x,_mm_setzero_ps());
    masky_lt  = _mm_cmplt_ps(y,_mm_setzero_ps());
    maskx_eq  = _mm_cmpeq_ps(x,_mm_setzero_ps());
    masky_eq  = _mm_cmpeq_ps(y,_mm_setzero_ps());

    z         = _mm_mul_ps(y,gmx_mm_inv_ps(x));
    z         = gmx_mm_atan_ps(z);

    mask1     = _mm_and_ps(maskx_eq,masky_lt);
    mask2     = _mm_andnot_ps(maskx_lt,masky_eq);
    mask3     = _mm_andnot_ps( _mm_or_ps(masky_lt,masky_eq) , maskx_eq);
    mask4     = _mm_and_ps(masky_eq,maskx_lt);

    maskall   = _mm_or_ps( _mm_or_ps(mask1,mask2), _mm_or_ps(mask3,mask4) );

    z         = _mm_andnot_ps(maskall,z);
    z1        = _mm_and_ps(mask1,minushalfpi);
    z3        = _mm_and_ps(mask3,halfpi);
    z4        = _mm_and_ps(mask4,pi);

    z         = _mm_or_ps( _mm_or_ps(z,z1), _mm_or_ps(z3,z4) );

    mask1     = _mm_andnot_ps(masky_lt,maskx_lt);
    mask2     = _mm_and_ps(maskx_lt,masky_lt);

    w         = _mm_or_ps( _mm_and_ps(mask1,pi), _mm_and_ps(mask2,minuspi) );
    w         = _mm_andnot_ps(maskall,w);

    z         = _mm_add_ps(z,w);

    return z;
}



#endif /* _gmx_math_x86_sse4_1_single_h_ */