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https://github.com/vale981/arb
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89545adbcc
Save some memory by using smaller arrays for the even and odd terms. Adjust the loop lengths, to accomodate for shorter arrays not overwriting "outdated" data. E.g.: If a and b are aliased, then the first poly_mul does not overwrite the leading coefficient, which leads to incorrect results.
61 lines
1.5 KiB
C
61 lines
1.5 KiB
C
/*
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Copyright (C) 2021 Matthias Gessinger
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This file is part of Arb.
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Arb is free software: you can redistribute it and/or modify it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include "acb_poly.h"
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void
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_acb_poly_graeffe_transform(acb_ptr b, acb_srcptr a, slong len, slong prec)
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{
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slong lo, le, ls;
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slong i;
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acb_ptr pe, po;
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if (len <= 1)
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{
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_acb_vec_set(b, a, len);
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return;
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}
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lo = len / 2;
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ls = 2 * lo - 1;
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le = (len - 1) / 2 + 1;
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po = _acb_vec_init(lo);
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pe = _acb_vec_init(FLINT_MAX(le, ls));
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for (i = len - 1; i >= 0; i--)
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{
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if (i % 2 == 0)
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acb_set(pe + i / 2, a + i);
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else
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acb_set(po + i / 2, a + i);
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}
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_acb_poly_mul(b, pe, le, pe, le, prec);
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_acb_poly_mul(pe, po, lo, po, lo, prec);
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_acb_poly_sub(b + 1, b + 1, ls, pe, ls, prec);
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if (len % 2 == 0)
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{
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_acb_vec_neg(b, b, len - 1);
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acb_set(b + (len - 1), pe + (len - 2));
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}
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_acb_vec_clear(pe, FLINT_MAX(le, ls));
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_acb_vec_clear(po, lo);
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}
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void
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acb_poly_graeffe_transform(acb_poly_t b, const acb_poly_t a, slong prec)
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{
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acb_poly_fit_length(b, a->length);
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_acb_poly_graeffe_transform(b->coeffs, a->coeffs, a->length, prec);
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_acb_poly_set_length(b, a->length);
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}
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