/**
 * @file llquaternion.cpp
 * @brief LLQuaternion class implementation.
 *
 * $LicenseInfo:firstyear=2000&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 *
 * 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;
 * version 2.1 of the License only.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#include "linden_common.h"

#include "llmath.h" // for F_PI

#include "llquaternion.h"

#include "v3math.h"
#include "v3dmath.h"
#include "v4math.h"
#include "m4math.h"
#include "m3math.h"
#include "llquantize.h"

// WARNING: Don't use this for global const definitions!  using this
// at the top of a *.cpp file might not give you what you think.
const LLQuaternion LLQuaternion::DEFAULT;

// Constructors

LLQuaternion::LLQuaternion(const LLMatrix4 &mat)
{
    *this = mat.quaternion();
    normalize();
}

LLQuaternion::LLQuaternion(const LLMatrix3 &mat)
{
    *this = mat.quaternion();
    normalize();
}

LLQuaternion::LLQuaternion(F32 angle, const LLVector4 &vec)
{
    F32 mag = vec.length();
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
}

LLQuaternion::LLQuaternion(F32 angle, const LLVector3 &vec)
{
    F32 mag = vec.length();
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
}

LLQuaternion::LLQuaternion(const LLVector3 &x_axis,
                           const LLVector3 &y_axis,
                           const LLVector3 &z_axis)
{
    LLMatrix3 mat;
    mat.setRows(x_axis, y_axis, z_axis);
    *this = mat.quaternion();
    normalize();
}

LLQuaternion::LLQuaternion(const LLSD &sd)
{
    setValue(sd);
}

// Quatizations
void    LLQuaternion::quantize16(F32 lower, F32 upper)
{
    F32 x = mQ[VX];
    F32 y = mQ[VY];
    F32 z = mQ[VZ];
    F32 s = mQ[VS];

    x = U16_to_F32(F32_to_U16_ROUND(x, lower, upper), lower, upper);
    y = U16_to_F32(F32_to_U16_ROUND(y, lower, upper), lower, upper);
    z = U16_to_F32(F32_to_U16_ROUND(z, lower, upper), lower, upper);
    s = U16_to_F32(F32_to_U16_ROUND(s, lower, upper), lower, upper);

    mQ[VX] = x;
    mQ[VY] = y;
    mQ[VZ] = z;
    mQ[VS] = s;

    normalize();
}

void    LLQuaternion::quantize8(F32 lower, F32 upper)
{
    mQ[VX] = U8_to_F32(F32_to_U8_ROUND(mQ[VX], lower, upper), lower, upper);
    mQ[VY] = U8_to_F32(F32_to_U8_ROUND(mQ[VY], lower, upper), lower, upper);
    mQ[VZ] = U8_to_F32(F32_to_U8_ROUND(mQ[VZ], lower, upper), lower, upper);
    mQ[VS] = U8_to_F32(F32_to_U8_ROUND(mQ[VS], lower, upper), lower, upper);

    normalize();
}

// LLVector3 Magnitude and Normalization Functions


// Set LLQuaternion routines

const LLQuaternion& LLQuaternion::setAngleAxis(F32 angle, F32 x, F32 y, F32 z)
{
    F32 mag = sqrtf(x * x + y * y + z * z);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = x * s;
        mQ[VY] = y * s;
        mQ[VZ] = z * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

const LLQuaternion& LLQuaternion::setAngleAxis(F32 angle, const LLVector3 &vec)
{
    F32 mag = sqrtf(vec.mV[VX] * vec.mV[VX] + vec.mV[VY] * vec.mV[VY] + vec.mV[VZ] * vec.mV[VZ]);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

const LLQuaternion& LLQuaternion::setAngleAxis(F32 angle, const LLVector4 &vec)
{
    F32 mag = sqrtf(vec.mV[VX] * vec.mV[VX] + vec.mV[VY] * vec.mV[VY] + vec.mV[VZ] * vec.mV[VZ]);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

const LLQuaternion& LLQuaternion::setEulerAngles(F32 roll, F32 pitch, F32 yaw)
{
    LLMatrix3 rot_mat(roll, pitch, yaw);
    rot_mat.orthogonalize();
    *this = rot_mat.quaternion();

    normalize();
    return (*this);
}

// deprecated
const LLQuaternion& LLQuaternion::set(const LLMatrix3 &mat)
{
    *this = mat.quaternion();
    normalize();
    return (*this);
}

// deprecated
const LLQuaternion& LLQuaternion::set(const LLMatrix4 &mat)
{
    *this = mat.quaternion();
    normalize();
    return (*this);
}

// deprecated
const LLQuaternion& LLQuaternion::setQuat(F32 angle, F32 x, F32 y, F32 z)
{
    F32 mag = sqrtf(x * x + y * y + z * z);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = x * s;
        mQ[VY] = y * s;
        mQ[VZ] = z * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

// deprecated
const LLQuaternion& LLQuaternion::setQuat(F32 angle, const LLVector3 &vec)
{
    F32 mag = sqrtf(vec.mV[VX] * vec.mV[VX] + vec.mV[VY] * vec.mV[VY] + vec.mV[VZ] * vec.mV[VZ]);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

const LLQuaternion& LLQuaternion::setQuat(F32 angle, const LLVector4 &vec)
{
    F32 mag = sqrtf(vec.mV[VX] * vec.mV[VX] + vec.mV[VY] * vec.mV[VY] + vec.mV[VZ] * vec.mV[VZ]);
    if (mag > FP_MAG_THRESHOLD)
    {
        angle *= 0.5;
        F32 c = cosf(angle);
        F32 s = sinf(angle) / mag;
        mQ[VX] = vec.mV[VX] * s;
        mQ[VY] = vec.mV[VY] * s;
        mQ[VZ] = vec.mV[VZ] * s;
        mQ[VW] = c;
    }
    else
    {
        loadIdentity();
    }
    return (*this);
}

const LLQuaternion& LLQuaternion::setQuat(F32 roll, F32 pitch, F32 yaw)
{
    roll  *= 0.5f;
    pitch *= 0.5f;
    yaw   *= 0.5f;
    F32 sinX = sinf(roll);
    F32 cosX = cosf(roll);
    F32 sinY = sinf(pitch);
    F32 cosY = cosf(pitch);
    F32 sinZ = sinf(yaw);
    F32 cosZ = cosf(yaw);
    mQ[VW] = cosX * cosY * cosZ - sinX * sinY * sinZ;
    mQ[VX] = sinX * cosY * cosZ + cosX * sinY * sinZ;
    mQ[VY] = cosX * sinY * cosZ - sinX * cosY * sinZ;
    mQ[VZ] = cosX * cosY * sinZ + sinX * sinY * cosZ;
    return (*this);
}

const LLQuaternion& LLQuaternion::setQuat(const LLMatrix3 &mat)
{
    *this = mat.quaternion();
    normalize();
    return (*this);
}

const LLQuaternion& LLQuaternion::setQuat(const LLMatrix4 &mat)
{
    *this = mat.quaternion();
    normalize();
    return (*this);
//#if 1
//  // NOTE: LLQuaternion's are actually inverted with respect to
//  // the matrices, so this code also assumes inverted quaternions
//  // (-x, -y, -z, w). The result is that roll,pitch,yaw are applied
//  // in reverse order (yaw,pitch,roll).
//  F64 cosX = cos(roll);
//    F64 cosY = cos(pitch);
//    F64 cosZ = cos(yaw);
//
//    F64 sinX = sin(roll);
//    F64 sinY = sin(pitch);
//    F64 sinZ = sin(yaw);
//
//    mQ[VW] = (F32)sqrt(cosY*cosZ - sinX*sinY*sinZ + cosX*cosZ + cosX*cosY + 1.0)*.5;
//  if (fabs(mQ[VW]) < F_APPROXIMATELY_ZERO)
//  {
//      // null rotation, any axis will do
//      mQ[VX] = 0.0f;
//      mQ[VY] = 1.0f;
//      mQ[VZ] = 0.0f;
//  }
//  else
//  {
//      F32 inv_s = 1.0f / (4.0f * mQ[VW]);
//      mQ[VX] = (F32)-(-sinX*cosY - cosX*sinY*sinZ - sinX*cosZ) * inv_s;
//      mQ[VY] = (F32)-(-cosX*sinY*cosZ + sinX*sinZ - sinY) * inv_s;
//      mQ[VZ] = (F32)-(-cosY*sinZ - sinX*sinY*cosZ - cosX*sinZ) * inv_s;
//  }
//
//#else // This only works on a certain subset of roll/pitch/yaw
//
//  F64 cosX = cosf(roll/2.0);
//    F64 cosY = cosf(pitch/2.0);
//    F64 cosZ = cosf(yaw/2.0);
//
//    F64 sinX = sinf(roll/2.0);
//    F64 sinY = sinf(pitch/2.0);
//    F64 sinZ = sinf(yaw/2.0);
//
//    mQ[VW] = (F32)(cosX*cosY*cosZ + sinX*sinY*sinZ);
//    mQ[VX] = (F32)(sinX*cosY*cosZ - cosX*sinY*sinZ);
//    mQ[VY] = (F32)(cosX*sinY*cosZ + sinX*cosY*sinZ);
//    mQ[VZ] = (F32)(cosX*cosY*sinZ - sinX*sinY*cosZ);
//#endif
//
//  normalize();
//  return (*this);
}

// SJB: This code is correct for a logicly stored (non-transposed) matrix;
//      Our matrices are stored transposed, OpenGL style, so this generates the
//      INVERSE matrix, or the CORRECT matrix form an INVERSE quaternion.
//      Because we use similar logic in LLMatrix3::quaternion(),
//      we are internally consistant so everything works OK :)
LLMatrix3   LLQuaternion::getMatrix3(void) const
{
    LLMatrix3   mat;
    F32     xx, xy, xz, xw, yy, yz, yw, zz, zw;

    xx      = mQ[VX] * mQ[VX];
    xy      = mQ[VX] * mQ[VY];
    xz      = mQ[VX] * mQ[VZ];
    xw      = mQ[VX] * mQ[VW];

    yy      = mQ[VY] * mQ[VY];
    yz      = mQ[VY] * mQ[VZ];
    yw      = mQ[VY] * mQ[VW];

    zz      = mQ[VZ] * mQ[VZ];
    zw      = mQ[VZ] * mQ[VW];

    mat.mMatrix[0][0]  = 1.f - 2.f * ( yy + zz );
    mat.mMatrix[0][1]  =       2.f * ( xy + zw );
    mat.mMatrix[0][2]  =       2.f * ( xz - yw );

    mat.mMatrix[1][0]  =       2.f * ( xy - zw );
    mat.mMatrix[1][1]  = 1.f - 2.f * ( xx + zz );
    mat.mMatrix[1][2]  =       2.f * ( yz + xw );

    mat.mMatrix[2][0]  =       2.f * ( xz + yw );
    mat.mMatrix[2][1]  =       2.f * ( yz - xw );
    mat.mMatrix[2][2]  = 1.f - 2.f * ( xx + yy );

    return mat;
}

LLMatrix4   LLQuaternion::getMatrix4(void) const
{
    LLMatrix4   mat;
    F32     xx, xy, xz, xw, yy, yz, yw, zz, zw;

    xx      = mQ[VX] * mQ[VX];
    xy      = mQ[VX] * mQ[VY];
    xz      = mQ[VX] * mQ[VZ];
    xw      = mQ[VX] * mQ[VW];

    yy      = mQ[VY] * mQ[VY];
    yz      = mQ[VY] * mQ[VZ];
    yw      = mQ[VY] * mQ[VW];

    zz      = mQ[VZ] * mQ[VZ];
    zw      = mQ[VZ] * mQ[VW];

    mat.mMatrix[0][0]  = 1.f - 2.f * ( yy + zz );
    mat.mMatrix[0][1]  =       2.f * ( xy + zw );
    mat.mMatrix[0][2]  =       2.f * ( xz - yw );

    mat.mMatrix[1][0]  =       2.f * ( xy - zw );
    mat.mMatrix[1][1]  = 1.f - 2.f * ( xx + zz );
    mat.mMatrix[1][2]  =       2.f * ( yz + xw );

    mat.mMatrix[2][0]  =       2.f * ( xz + yw );
    mat.mMatrix[2][1]  =       2.f * ( yz - xw );
    mat.mMatrix[2][2]  = 1.f - 2.f * ( xx + yy );

    // TODO -- should we set the translation portion to zero?

    return mat;
}




// Other useful methods


// calculate the shortest rotation from a to b
void LLQuaternion::shortestArc(const LLVector3 &a, const LLVector3 &b)
{
    F32 ab = a * b; // dotproduct
    LLVector3 c = a % b; // crossproduct
    F32 cc = c * c; // squared length of the crossproduct
    if (ab * ab + cc) // test if the arguments have sufficient magnitude
    {
        if (cc > 0.0f) // test if the arguments are (anti)parallel
        {
            F32 s = sqrtf(ab * ab + cc) + ab; // note: don't try to optimize this line
            F32 m = 1.0f / sqrtf(cc + s * s); // the inverted magnitude of the quaternion
            mQ[VX] = c.mV[VX] * m;
            mQ[VY] = c.mV[VY] * m;
            mQ[VZ] = c.mV[VZ] * m;
            mQ[VW] = s * m;
            return;
        }
        if (ab < 0.0f) // test if the angle is bigger than PI/2 (anti parallel)
        {
            c = a - b; // the arguments are anti-parallel, we have to choose an axis
            F32 m = sqrtf(c.mV[VX] * c.mV[VX] +  c.mV[VY] * c.mV[VY]); // the length projected on the XY-plane
            if (m > FP_MAG_THRESHOLD)
            {
                mQ[VX] = -c.mV[VY] / m; // return the quaternion with the axis in the XY-plane
                mQ[VY] =  c.mV[VX] / m;
                mQ[VZ] = 0.0f;
                mQ[VW] = 0.0f;
                return;
            }
            else // the vectors are parallel to the Z-axis
            {
                mQ[VX] = 1.0f; // rotate around the X-axis
                mQ[VY] = 0.0f;
                mQ[VZ] = 0.0f;
                mQ[VW] = 0.0f;
                return;
            }
        }
    }
    loadIdentity();
}

// constrains rotation to a cone angle specified in radians
const LLQuaternion &LLQuaternion::constrain(F32 radians)
{
    const F32 cos_angle_lim = cosf( radians/2 );    // mQ[VW] limit
    const F32 sin_angle_lim = sinf( radians/2 );    // rotation axis length limit

    if (mQ[VW] < 0.f)
    {
        mQ[VX] *= -1.f;
        mQ[VY] *= -1.f;
        mQ[VZ] *= -1.f;
        mQ[VW] *= -1.f;
    }

    // if rotation angle is greater than limit (cos is less than limit)
    if( mQ[VW] < cos_angle_lim )
    {
        mQ[VW] = cos_angle_lim;
        F32 axis_len = sqrtf( mQ[VX]*mQ[VX] + mQ[VY]*mQ[VY] + mQ[VZ]*mQ[VZ] ); // sin(theta/2)
        F32 axis_mult_fact = sin_angle_lim / axis_len;
        mQ[VX] *= axis_mult_fact;
        mQ[VY] *= axis_mult_fact;
        mQ[VZ] *= axis_mult_fact;
    }

    return *this;
}

// Operators

std::ostream& operator<<(std::ostream &s, const LLQuaternion &a)
{
    s << "{ "
        << a.mQ[VX] << ", " << a.mQ[VY] << ", " << a.mQ[VZ] << ", " << a.mQ[VW]
    << " }";
    return s;
}


// Does NOT renormalize the result
LLQuaternion    operator*(const LLQuaternion &a, const LLQuaternion &b)
{
//  LLQuaternion::mMultCount++;

    LLQuaternion q(
        b.mQ[3] * a.mQ[0] + b.mQ[0] * a.mQ[3] + b.mQ[1] * a.mQ[2] - b.mQ[2] * a.mQ[1],
        b.mQ[3] * a.mQ[1] + b.mQ[1] * a.mQ[3] + b.mQ[2] * a.mQ[0] - b.mQ[0] * a.mQ[2],
        b.mQ[3] * a.mQ[2] + b.mQ[2] * a.mQ[3] + b.mQ[0] * a.mQ[1] - b.mQ[1] * a.mQ[0],
        b.mQ[3] * a.mQ[3] - b.mQ[0] * a.mQ[0] - b.mQ[1] * a.mQ[1] - b.mQ[2] * a.mQ[2]
    );
    return q;
}

/*
LLMatrix4   operator*(const LLMatrix4 &m, const LLQuaternion &q)
{
    LLMatrix4 qmat(q);
    return (m*qmat);
}
*/



LLVector4       operator*(const LLVector4 &a, const LLQuaternion &rot)
{
    F32 rw = - rot.mQ[VX] * a.mV[VX] - rot.mQ[VY] * a.mV[VY] - rot.mQ[VZ] * a.mV[VZ];
    F32 rx =   rot.mQ[VW] * a.mV[VX] + rot.mQ[VY] * a.mV[VZ] - rot.mQ[VZ] * a.mV[VY];
    F32 ry =   rot.mQ[VW] * a.mV[VY] + rot.mQ[VZ] * a.mV[VX] - rot.mQ[VX] * a.mV[VZ];
    F32 rz =   rot.mQ[VW] * a.mV[VZ] + rot.mQ[VX] * a.mV[VY] - rot.mQ[VY] * a.mV[VX];

    F32 nx = - rw * rot.mQ[VX] +  rx * rot.mQ[VW] - ry * rot.mQ[VZ] + rz * rot.mQ[VY];
    F32 ny = - rw * rot.mQ[VY] +  ry * rot.mQ[VW] - rz * rot.mQ[VX] + rx * rot.mQ[VZ];
    F32 nz = - rw * rot.mQ[VZ] +  rz * rot.mQ[VW] - rx * rot.mQ[VY] + ry * rot.mQ[VX];

    return LLVector4(nx, ny, nz, a.mV[VW]);
}

LLVector3       operator*(const LLVector3 &a, const LLQuaternion &rot)
{
    F32 rw = - rot.mQ[VX] * a.mV[VX] - rot.mQ[VY] * a.mV[VY] - rot.mQ[VZ] * a.mV[VZ];
    F32 rx =   rot.mQ[VW] * a.mV[VX] + rot.mQ[VY] * a.mV[VZ] - rot.mQ[VZ] * a.mV[VY];
    F32 ry =   rot.mQ[VW] * a.mV[VY] + rot.mQ[VZ] * a.mV[VX] - rot.mQ[VX] * a.mV[VZ];
    F32 rz =   rot.mQ[VW] * a.mV[VZ] + rot.mQ[VX] * a.mV[VY] - rot.mQ[VY] * a.mV[VX];

    F32 nx = - rw * rot.mQ[VX] +  rx * rot.mQ[VW] - ry * rot.mQ[VZ] + rz * rot.mQ[VY];
    F32 ny = - rw * rot.mQ[VY] +  ry * rot.mQ[VW] - rz * rot.mQ[VX] + rx * rot.mQ[VZ];
    F32 nz = - rw * rot.mQ[VZ] +  rz * rot.mQ[VW] - rx * rot.mQ[VY] + ry * rot.mQ[VX];

    return LLVector3(nx, ny, nz);
}

LLVector3d      operator*(const LLVector3d &a, const LLQuaternion &rot)
{
    F64 rw = - rot.mQ[VX] * a.mdV[VX] - rot.mQ[VY] * a.mdV[VY] - rot.mQ[VZ] * a.mdV[VZ];
    F64 rx =   rot.mQ[VW] * a.mdV[VX] + rot.mQ[VY] * a.mdV[VZ] - rot.mQ[VZ] * a.mdV[VY];
    F64 ry =   rot.mQ[VW] * a.mdV[VY] + rot.mQ[VZ] * a.mdV[VX] - rot.mQ[VX] * a.mdV[VZ];
    F64 rz =   rot.mQ[VW] * a.mdV[VZ] + rot.mQ[VX] * a.mdV[VY] - rot.mQ[VY] * a.mdV[VX];

    F64 nx = - rw * rot.mQ[VX] +  rx * rot.mQ[VW] - ry * rot.mQ[VZ] + rz * rot.mQ[VY];
    F64 ny = - rw * rot.mQ[VY] +  ry * rot.mQ[VW] - rz * rot.mQ[VX] + rx * rot.mQ[VZ];
    F64 nz = - rw * rot.mQ[VZ] +  rz * rot.mQ[VW] - rx * rot.mQ[VY] + ry * rot.mQ[VX];

    return LLVector3d(nx, ny, nz);
}

F32 dot(const LLQuaternion &a, const LLQuaternion &b)
{
    return a.mQ[VX] * b.mQ[VX] +
           a.mQ[VY] * b.mQ[VY] +
           a.mQ[VZ] * b.mQ[VZ] +
           a.mQ[VW] * b.mQ[VW];
}

// DEMO HACK: This lerp is probably inocrrect now due intermediate normalization
// it should look more like the lerp below
#if 0
// linear interpolation
LLQuaternion lerp(F32 t, const LLQuaternion &p, const LLQuaternion &q)
{
    LLQuaternion r;
    r = t * (q - p) + p;
    r.normalize();
    return r;
}
#endif

// lerp from identity to q
LLQuaternion lerp(F32 t, const LLQuaternion &q)
{
    LLQuaternion r;
    r.mQ[VX] = t * q.mQ[VX];
    r.mQ[VY] = t * q.mQ[VY];
    r.mQ[VZ] = t * q.mQ[VZ];
    r.mQ[VW] = t * (q.mQ[VZ] - 1.f) + 1.f;
    r.normalize();
    return r;
}

LLQuaternion lerp(F32 t, const LLQuaternion &p, const LLQuaternion &q)
{
    LLQuaternion r;
    F32 inv_t;

    inv_t = 1.f - t;

    r.mQ[VX] = t * q.mQ[VX] + (inv_t * p.mQ[VX]);
    r.mQ[VY] = t * q.mQ[VY] + (inv_t * p.mQ[VY]);
    r.mQ[VZ] = t * q.mQ[VZ] + (inv_t * p.mQ[VZ]);
    r.mQ[VW] = t * q.mQ[VW] + (inv_t * p.mQ[VW]);
    r.normalize();
    return r;
}


// spherical linear interpolation
LLQuaternion slerp( F32 u, const LLQuaternion &a, const LLQuaternion &b )
{
    // cosine theta = dot product of a and b
    F32 cos_t = a.mQ[0]*b.mQ[0] + a.mQ[1]*b.mQ[1] + a.mQ[2]*b.mQ[2] + a.mQ[3]*b.mQ[3];

    // if b is on opposite hemisphere from a, use -a instead
    bool bflip;
    if (cos_t < 0.0f)
    {
        cos_t = -cos_t;
        bflip = true;
    }
    else
        bflip = false;

    // if B is (within precision limits) the same as A,
    // just linear interpolate between A and B.
    F32 alpha;  // interpolant
    F32 beta;       // 1 - interpolant
    if (1.0f - cos_t < 0.00001f)
    {
        beta = 1.0f - u;
        alpha = u;
    }
    else
    {
        F32 theta = acosf(cos_t);
        F32 sin_t = sinf(theta);
        beta = sinf(theta - u*theta) / sin_t;
        alpha = sinf(u*theta) / sin_t;
    }

    if (bflip)
        beta = -beta;

    // interpolate
    LLQuaternion ret;
    ret.mQ[0] = beta*a.mQ[0] + alpha*b.mQ[0];
    ret.mQ[1] = beta*a.mQ[1] + alpha*b.mQ[1];
    ret.mQ[2] = beta*a.mQ[2] + alpha*b.mQ[2];
    ret.mQ[3] = beta*a.mQ[3] + alpha*b.mQ[3];

    return ret;
}

// lerp whenever possible
LLQuaternion nlerp(F32 t, const LLQuaternion &a, const LLQuaternion &b)
{
    if (dot(a, b) < 0.f)
    {
        return slerp(t, a, b);
    }
    else
    {
        return lerp(t, a, b);
    }
}

LLQuaternion nlerp(F32 t, const LLQuaternion &q)
{
    if (q.mQ[VW] < 0.f)
    {
        return slerp(t, q);
    }
    else
    {
        return lerp(t, q);
    }
}

// slerp from identity quaternion to another quaternion
LLQuaternion slerp(F32 t, const LLQuaternion &q)
{
    F32 c = q.mQ[VW];
    if (1.0f == t  ||  1.0f == c)
    {
        // the trivial cases
        return q;
    }

    LLQuaternion r;
    F32 s, angle, stq, stp;

    s = (F32) sqrt(1.f - c*c);

    if (c < 0.0f)
    {
        // when c < 0.0 then theta > PI/2
        // since quat and -quat are the same rotation we invert one of
        // p or q to reduce unecessary spins
        // A equivalent way to do it is to convert acos(c) as if it had
        // been negative, and to negate stp
        angle   = (F32) acos(-c);
        stp     = -(F32) sin(angle * (1.f - t));
        stq     = (F32) sin(angle * t);
    }
    else
    {
        angle   = (F32) acos(c);
        stp     = (F32) sin(angle * (1.f - t));
        stq     = (F32) sin(angle * t);
    }

    r.mQ[VX] = (q.mQ[VX] * stq) / s;
    r.mQ[VY] = (q.mQ[VY] * stq) / s;
    r.mQ[VZ] = (q.mQ[VZ] * stq) / s;
    r.mQ[VW] = (stp + q.mQ[VW] * stq) / s;

    return r;
}

LLQuaternion mayaQ(F32 xRot, F32 yRot, F32 zRot, LLQuaternion::Order order)
{
    LLQuaternion xQ( xRot*DEG_TO_RAD, LLVector3(1.0f, 0.0f, 0.0f) );
    LLQuaternion yQ( yRot*DEG_TO_RAD, LLVector3(0.0f, 1.0f, 0.0f) );
    LLQuaternion zQ( zRot*DEG_TO_RAD, LLVector3(0.0f, 0.0f, 1.0f) );
    LLQuaternion ret;
    switch( order )
    {
    case LLQuaternion::XYZ:
        ret = xQ * yQ * zQ;
        break;
    case LLQuaternion::YZX:
        ret = yQ * zQ * xQ;
        break;
    case LLQuaternion::ZXY:
        ret = zQ * xQ * yQ;
        break;
    case LLQuaternion::XZY:
        ret = xQ * zQ * yQ;
        break;
    case LLQuaternion::YXZ:
        ret = yQ * xQ * zQ;
        break;
    case LLQuaternion::ZYX:
        ret = zQ * yQ * xQ;
        break;
    }
    return ret;
}

const char *OrderToString( const LLQuaternion::Order order )
{
    const char *p = NULL;
    switch( order )
    {
    default:
    case LLQuaternion::XYZ:
        p = "XYZ";
        break;
    case LLQuaternion::YZX:
        p = "YZX";
        break;
    case LLQuaternion::ZXY:
        p = "ZXY";
        break;
    case LLQuaternion::XZY:
        p = "XZY";
        break;
    case LLQuaternion::YXZ:
        p = "YXZ";
        break;
    case LLQuaternion::ZYX:
        p = "ZYX";
        break;
    }
    return p;
}

LLQuaternion::Order StringToOrder( const char *str )
{
    if (strncmp(str, "XYZ", 3)==0 || strncmp(str, "xyz", 3)==0)
        return LLQuaternion::XYZ;

    if (strncmp(str, "YZX", 3)==0 || strncmp(str, "yzx", 3)==0)
        return LLQuaternion::YZX;

    if (strncmp(str, "ZXY", 3)==0 || strncmp(str, "zxy", 3)==0)
        return LLQuaternion::ZXY;

    if (strncmp(str, "XZY", 3)==0 || strncmp(str, "xzy", 3)==0)
        return LLQuaternion::XZY;

    if (strncmp(str, "YXZ", 3)==0 || strncmp(str, "yxz", 3)==0)
        return LLQuaternion::YXZ;

    if (strncmp(str, "ZYX", 3)==0 || strncmp(str, "zyx", 3)==0)
        return LLQuaternion::ZYX;

    return LLQuaternion::XYZ;
}

void LLQuaternion::getAngleAxis(F32* angle, LLVector3 &vec) const
{
    F32 v = sqrtf(mQ[VX] * mQ[VX] + mQ[VY] * mQ[VY] + mQ[VZ] * mQ[VZ]); // length of the vector-component
    if (v > FP_MAG_THRESHOLD)
    {
        F32 oomag = 1.0f / v;
        F32 w = mQ[VW];
        if (mQ[VW] < 0.0f)
        {
            w = -w; // make VW positive
            oomag = -oomag; // invert the axis
        }
        vec.mV[VX] = mQ[VX] * oomag; // normalize the axis
        vec.mV[VY] = mQ[VY] * oomag;
        vec.mV[VZ] = mQ[VZ] * oomag;
        *angle = 2.0f * atan2f(v, w); // get the angle
    }
    else
    {
        *angle = 0.0f; // no rotation
        vec.mV[VX] = 0.0f; // around some dummy axis
        vec.mV[VY] = 0.0f;
        vec.mV[VZ] = 1.0f;
    }
}

const LLQuaternion& LLQuaternion::setFromAzimuthAndAltitude(F32 azimuthRadians, F32 altitudeRadians)
{
    // euler angle inputs are complements of azimuth/altitude which are measured from zenith
    F32 pitch = llclamp(F_PI_BY_TWO - altitudeRadians, 0.0f, F_PI_BY_TWO);
    F32 yaw   = llclamp(F_PI_BY_TWO - azimuthRadians,  0.0f, F_PI_BY_TWO);
    setEulerAngles(0.0f, pitch, yaw);
    return *this;
}

void LLQuaternion::getAzimuthAndAltitude(F32 &azimuthRadians, F32 &altitudeRadians)
{
    F32 rick_roll;
    F32 pitch;
    F32 yaw;
    getEulerAngles(&rick_roll, &pitch, &yaw);
    // make these measured from zenith
    altitudeRadians = llclamp(F_PI_BY_TWO - pitch, 0.0f, F_PI_BY_TWO);
    azimuthRadians  = llclamp(F_PI_BY_TWO - yaw,   0.0f, F_PI_BY_TWO);
}

// quaternion does not need to be normalized
void LLQuaternion::getEulerAngles(F32 *roll, F32 *pitch, F32 *yaw) const
{
    F32 sx = 2 * (mQ[VX] * mQ[VW] - mQ[VY] * mQ[VZ]); // sine of the roll
    F32 sy = 2 * (mQ[VY] * mQ[VW] + mQ[VX] * mQ[VZ]); // sine of the pitch
    F32 ys = mQ[VW] * mQ[VW] - mQ[VY] * mQ[VY]; // intermediate cosine 1
    F32 xz = mQ[VX] * mQ[VX] - mQ[VZ] * mQ[VZ]; // intermediate cosine 2
    F32 cx = ys - xz; // cosine of the roll
    F32 cy = sqrtf(sx * sx + cx * cx); // cosine of the pitch
    if (cy > GIMBAL_THRESHOLD) // no gimbal lock
    {
        *roll  = atan2f(sx, cx);
        *pitch = atan2f(sy, cy);
        *yaw   = atan2f(2 * (mQ[VZ] * mQ[VW] - mQ[VX] * mQ[VY]), ys + xz);
    }
    else // gimbal lock
    {
        if (sy > 0)
        {
            *pitch = F_PI_BY_TWO;
            *yaw = 2 * atan2f(mQ[VZ] + mQ[VX], mQ[VW] + mQ[VY]);
        }
        else
        {
            *pitch = -F_PI_BY_TWO;
            *yaw = 2 * atan2f(mQ[VZ] - mQ[VX], mQ[VW] - mQ[VY]);
        }
        *roll = 0;
    }
}

// Saves space by using the fact that our quaternions are normalized
LLVector3 LLQuaternion::packToVector3() const
{
    F32 x = mQ[VX];
    F32 y = mQ[VY];
    F32 z = mQ[VZ];
    F32 w = mQ[VW];
    F32 mag = sqrtf(x * x + y * y + z * z + w * w);
    if (mag > FP_MAG_THRESHOLD)
    {
        x /= mag;
        y /= mag;
        z /= mag; // no need to normalize w, it's not used
    }
    if( mQ[VW] >= 0 )
    {
        return LLVector3( x, y , z );
    }
    else
    {
        return LLVector3( -x, -y, -z );
    }
}

// Saves space by using the fact that our quaternions are normalized
void LLQuaternion::unpackFromVector3( const LLVector3& vec )
{
    mQ[VX] = vec.mV[VX];
    mQ[VY] = vec.mV[VY];
    mQ[VZ] = vec.mV[VZ];
    F32 t = 1.f - vec.magVecSquared();
    if( t > 0 )
    {
        mQ[VW] = sqrt( t );
    }
    else
    {
        // Need this to avoid trying to find the square root of a negative number due
        // to floating point error.
        mQ[VW] = 0;
    }
}

bool LLQuaternion::parseQuat(const std::string& buf, LLQuaternion* value)
{
    if( buf.empty() || value == NULL)
    {
        return false;
    }

    LLQuaternion quat;
    S32 count = sscanf( buf.c_str(), "%f %f %f %f", quat.mQ + 0, quat.mQ + 1, quat.mQ + 2, quat.mQ + 3 );
    if( 4 == count )
    {
        value->set( quat );
        return true;
    }

    return false;
}


// End