1 /*
2 Copyright (C) 2012 Sebastian Pancratz
3 Copyright (C) 2013 Mike Hansen
4
5 This file is part of FLINT.
6
7 FLINT is free software: you can redistribute it and/or modify it under
8 the terms of the GNU Lesser General Public License (LGPL) as published
9 by the Free Software Foundation; either version 2.1 of the License, or
10 (at your option) any later version. See <http://www.gnu.org/licenses/>.
11 */
12
13 #include "ulong_extras.h"
14 #include "fq.h"
15
16 /*
17 Sets (rop, 2d-1) to the image of (op, len) under the Frobenius operator
18 raised to the e-th power, assuming that neither op nor e are zero.
19 */
20
21 void
_fq_frobenius(fmpz * rop,const fmpz * op,slong len,slong e,const fq_ctx_t ctx)22 _fq_frobenius(fmpz * rop, const fmpz * op, slong len, slong e, const fq_ctx_t ctx)
23 {
24 const slong d = fq_ctx_degree(ctx);
25
26 if (len == 1) /* op is in Fp, not just Fq */
27 {
28 _fmpz_vec_set(rop, op, len);
29 _fmpz_vec_zero(rop + len, (2 * d - 1) - len);
30 }
31 else
32 {
33 fmpz_t t;
34
35 fmpz_init(t);
36 fmpz_pow_ui(t, fq_ctx_prime(ctx), e);
37 _fq_pow(rop, op, len, t, ctx);
38 fmpz_clear(t);
39 }
40 }
41
42 void
fq_frobenius(fq_t rop,const fq_t op,slong e,const fq_ctx_t ctx)43 fq_frobenius(fq_t rop, const fq_t op, slong e, const fq_ctx_t ctx)
44 {
45 const slong d = fq_ctx_degree(ctx);
46
47 e = e % d;
48 if (e < 0)
49 e += d;
50
51 if (fq_is_zero(op, ctx))
52 {
53 fq_zero(rop, ctx);
54 }
55 else if (e == 0)
56 {
57 fq_set(rop, op, ctx);
58 }
59 else
60 {
61 fmpz *t;
62
63 if (rop == op)
64 {
65 t = _fmpz_vec_init(2 * d - 1);
66 }
67 else
68 {
69 fmpz_poly_fit_length(rop, 2 * d - 1);
70 t = rop->coeffs;
71 }
72
73 _fq_frobenius(t, op->coeffs, op->length, e, ctx);
74
75 if (rop == op)
76 {
77 _fmpz_vec_clear(rop->coeffs, rop->alloc);
78 rop->coeffs = t;
79 rop->alloc = 2 * d - 1;
80 rop->length = d;
81 }
82 else
83 {
84 _fmpz_poly_set_length(rop, d);
85 }
86 _fmpz_poly_normalise(rop);
87 }
88 }
89