1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
/*
Copyright (C) 2013 Mike Hansen
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 "ulong_extras.h"
#include "fq_zech.h"
void
fq_zech_sub(fq_zech_t rop, const fq_zech_t op1, const fq_zech_t op2,
const fq_zech_ctx_t ctx)
{
ulong index, c;
if (op2->value == ctx->qm1)
{
rop->value = op1->value;
}
else if (op1->value == ctx->qm1)
{
fq_zech_neg(rop, op2, ctx);
}
else
{
index = n_submod(op2->value, op1->value, ctx->qm1);
index = n_submod(index, ctx->qm1o2, ctx->qm1);
c = ctx->zech_log_table[index];
if (c != ctx->qm1)
{
c = n_addmod(c, op1->value, ctx->qm1);
}
rop->value = c;
}
}