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/*
Copyright (C) 2014 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "acb.h"
#include "acb_modular.h"
void acb_modular_transform(acb_t w, const psl2z_t g, const acb_t z, slong prec)
{
#define a (&g->a)
#define b (&g->b)
#define c (&g->c)
#define d (&g->d)
#define x acb_realref(z)
#define y acb_imagref(z)
if (fmpz_is_zero(c))
{
/* (az+b)/d, where we must have a = d = 1 */
acb_add_fmpz(w, z, b, prec);
}
else if (fmpz_is_zero(a))
{
/* b/(cz+d), where -bc = 1, c = 1 => -1/(z+d) */
acb_add_fmpz(w, z, d, prec);
acb_inv(w, w, prec);
acb_neg(w, w);
}
else if (0)
{
acb_t t, u;
acb_init(t);
acb_init(u);
acb_set_fmpz(t, b);
acb_addmul_fmpz(t, z, a, prec);
acb_set_fmpz(u, d);
acb_addmul_fmpz(u, z, c, prec);
acb_div(w, t, u, prec);
acb_clear(t);
acb_clear(u);
}
else
{
/* (az+b)/(cz+d) = (re+im*i)/den where
re = bd + (bc+ad)x + ac(x^2+y^2)
im = (ad-bc)y
den = c^2(x^2+y^2) + 2cdx + d^2
*/
fmpz_t t;
arb_t re, im, den;
arb_init(re);
arb_init(im);
arb_init(den);
fmpz_init(t);
arb_mul(im, x, x, prec);
arb_addmul(im, y, y, prec);
fmpz_mul(t, b, d);
arb_set_fmpz(re, t);
fmpz_mul(t, b, c);
fmpz_addmul(t, a, d);
arb_addmul_fmpz(re, x, t, prec);
fmpz_mul(t, a, c);
arb_addmul_fmpz(re, im, t, prec);
fmpz_mul(t, d, d);
arb_set_fmpz(den, t);
fmpz_mul(t, c, d);
fmpz_mul_2exp(t, t, 1);
arb_addmul_fmpz(den, x, t, prec);
fmpz_mul(t, c, c);
arb_addmul_fmpz(den, im, t, prec);
fmpz_mul(t, a, d);
fmpz_submul(t, b, c);
arb_mul_fmpz(im, y, t, prec);
arb_div(acb_realref(w), re, den, prec);
arb_div(acb_imagref(w), im, den, prec);
arb_clear(re);
arb_clear(im);
arb_clear(den);
fmpz_clear(t);
}
#undef a
#undef b
#undef c
#undef d
#undef x
#undef y
}