"""basic special functions


cotdg and tandg implementations are adapted from the following SciPy code:

https://github.com/scipy/scipy/blob/master/scipy/special/cephes/tandg.c

radian is from

https://github.com/scipy/scipy/blob/master/scipy/special/cephes/sindg.c

cosm1 is from

https://github.com/scipy/scipy/blob/main/scipy/special/cephes/unity.c

polevl is from

https://github.com/scipy/scipy/blob/main/scipy/special/cephes/polevl.h


Cephes Math Library Release 2.0:  April, 1987
Copyright 1984, 1987 by Stephen L. Moshier
Direct inquiries to 30 Frost Street, Cambridge, MA 02140
"""

from cupy import _core


# Note: cast complex<single> to complex<double> or tests fail tolerance
log1p = _core.create_ufunc(
    'cupyx_scipy_log1p',
    (('f->f', 'out0 = log1pf(in0)'),
     ('F->F', 'out0 = out0_type(log1p((complex<double>)in0))'),
     'd->d', 'D->D'),
    'out0 = log1p(in0);',
    doc="""Elementwise function for scipy.special.log1p

    Calculates log(1 + x) for use when `x` is near zero.

    Notes
    -----
    This implementation currently does not support complex-valued `x`.

    .. seealso:: :meth:`scipy.special.log1p`

    """,
)


cbrt = _core.create_ufunc(
    'cupyx_scipy_special_cbrt',
    (('f->f', 'out0 = cbrtf(in0)'), 'd->d'),
    'out0 = cbrt(in0)',
    doc='''Cube root.

    .. seealso:: :meth:`scipy.special.cbrt`

    ''')


exp2 = _core.create_ufunc(
    'cupyx_scipy_special_exp2',
    (('f->f', 'out0 = exp2f(in0)'), 'd->d'),
    'out0 = exp2(in0)',
    doc='''Computes ``2**x``.

    .. seealso:: :meth:`scipy.special.exp2`

    ''')


exp10 = _core.create_ufunc(
    'cupyx_scipy_special_exp10',
    (('f->f', 'out0 = exp10f(in0)'), 'd->d'),
    'out0 = exp10(in0)',
    doc='''Computes ``10**x``.

    .. seealso:: :meth:`scipy.special.exp10`

    ''')


expm1 = _core.create_ufunc(
    'cupyx_scipy_special_expm1',
    (('f->f', 'out0 = expm1f(in0)'), 'd->d', 'F->F', 'D->D'),
    'out0 = expm1(in0)',
    doc='''Computes ``exp(x) - 1``.

    .. seealso:: :meth:`scipy.special.expm1`

    ''')

exprel = _core.create_ufunc(
    'cupyx_scipy_special_exprel',
    (('f->f'), 'd->d', 'F->F', 'D->D'),
    'out0 = abs(in0) >= 1e-16 ? expm1(in0) / in0 : 1',
    doc='''Computes ``(exp(x) - 1) / x``.

    .. seealso:: :meth:`scipy.special.exprel`

    ''')

cosm1_implementation = """
//Define from npy_math.h
//https://github.com/numpy/numpy/blob/main/numpy/core/include/numpy/npy_math.h
#define NPY_PI_4      0.785398163397448309615660845819875721  /* pi/4 */
__constant__ double coscof[] = {
    4.7377507964246204691685E-14,
    -1.1470284843425359765671E-11,
    2.0876754287081521758361E-9,
    -2.7557319214999787979814E-7,
    2.4801587301570552304991E-5,
    -1.3888888888888872993737E-3,
    4.1666666666666666609054E-2,
};

__device__ static double polevl(double x, const double coef[], int N)
{
    double ans;
    int i;
    const double *p;

    p = coef;
    ans = *p++;
    i = N;

    do
        ans = ans * x + *p++;
    while (--i);

    return (ans);
}

__device__ static double cosm1(double x)
{
    double xx;

    if ((x < -NPY_PI_4) || (x > NPY_PI_4))
        return (cos(x) - 1.0);
    xx = x * x;
    xx = -0.5 * xx + xx * xx * polevl(xx, coscof, 6);
    return xx;
}
"""

cosm1 = _core.create_ufunc(
    'cupyx_scipy_special_cosm1', ('f->f', 'd->d'),
    'out0 = cosm1(in0)',
    preamble=cosm1_implementation,
    doc='''Computes ``cos(x) - 1``.

    .. seealso:: :meth:`scipy.special.cosm1`

    ''')

pi180_preamble = """
    __constant__ double PI180 = 1.74532925199432957692E-2;  // pi/180
"""

cosdg = _core.create_ufunc(
    'cupyx_scipy_special_cosdg',
    (('f->f', 'out0 = cosf(PI180 * in0)'), 'd->d'),
    'out0 = cos(PI180 * in0)',
    preamble=pi180_preamble,
    doc='''Cosine of x with x in degrees.

    .. seealso:: :meth:`scipy.special.cosdg`

    ''')


sindg = _core.create_ufunc(
    'cupyx_scipy_special_sindg',
    (('f->f', 'out0 = sinf(PI180 * in0)'), 'd->d'),
    'out0 = sin(PI180 * in0)',
    preamble=pi180_preamble,
    doc='''Sine of x with x in degrees.

    .. seealso:: :meth:`scipy.special.sindg`

    ''')


tancot_implementation = pi180_preamble + """


// include for CUDART_INF
#include <cupy/math_constants.h>

__constant__ double  lossth = 1.0e14;

__device__ static double tancot(double, int);

__device__ static double tandg(double x)
{
    return tancot(x, 0);
}


__device__ static double cotdg(double x)
{
    return tancot(x, 1);
}


__device__ static double tancot(double xx, int cotflg)
{
    double x;
    int sign;

    /* make argument positive but save the sign */
    if (xx < 0) {
        x = -xx;
        sign = -1;
    }
    else {
        x = xx;
        sign = 1;
    }

    if (x > lossth) {
        // sf_error("tandg", SF_ERROR_NO_RESULT, NULL);
        return 0.0;
    }

    /* modulo 180 */
    x = x - 180.0 * floor(x / 180.0);
    if (cotflg) {
        if (x <= 90.0) {
            x = 90.0 - x;
        } else {
            x = x - 90.0;
            sign *= -1;
        }
    } else {
        if (x > 90.0) {
            x = 180.0 - x;
            sign *= -1;
        }
    }
    if (x == 0.0) {
        return 0.0;
    }
    else if (x == 45.0) {
        return sign * 1.0;
    }
    else if (x == 90.0) {
        // sf_error((cotflg ? "cotdg" : "tandg"), SF_ERROR_SINGULAR, NULL);
        return CUDART_INF;
    }
    /* x is now transformed into [0, 90) */
    return sign * tan(x * PI180);
}
"""

tandg = _core.create_ufunc(
    'cupyx_scipy_special_tandg', ('f->f', 'd->d'),
    'out0 = tandg(in0)',
    preamble=tancot_implementation,
    doc='''Tangent of x with x in degrees.

    .. seealso:: :meth:`scipy.special.tandg`

    ''')


cotdg = _core.create_ufunc(
    'cupyx_scipy_special_cotdg', ('f->f', 'd->d'),
    'out0 = cotdg(in0)',
    preamble=tancot_implementation,
    doc='''Cotangent of x with x in degrees.

    .. seealso:: :meth:`scipy.special.cotdg`

    ''')

radian_implementation = """
/* 1 arc second, in radians*/
__constant__ double P64800 =
    4.848136811095359935899141023579479759563533023727e-6;

template <typename T>
__device__ T radian(T d, T m, T s)
{
    return (((d * 60.0 + m) * 60.0 + s) * P64800);
}
"""

radian = _core.create_ufunc(
    'cupyx_scipy_special_radian', ('fff->f', 'ddd->d'),
    'out0 = radian(in0, in1, in2)',
    preamble=radian_implementation,
    doc='''Degrees, minutes, seconds to radians:

    .. seealso:: :meth:`scipy.special.radian`

    ''')