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comparison 3rdparty/libtommath/bn_mp_is_square.c @ 0:2cf249471370

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author Takahiro SHIMIZU <anatofuz@cr.ie.u-ryukyu.ac.jp>
date Tue, 08 May 2018 16:09:12 +0900
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1 #include <tommath_private.h>
2 #ifdef BN_MP_IS_SQUARE_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
16 */
17
18 /* Check if remainders are possible squares - fast exclude non-squares */
19 static const char rem_128[128] = {
20 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
21 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
22 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
23 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
24 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
25 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
26 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
27 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1
28 };
29
30 static const char rem_105[105] = {
31 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
32 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1,
33 0, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
34 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1,
35 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1,
36 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1,
37 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1
38 };
39
40 /* Store non-zero to ret if arg is square, and zero if not */
41 int mp_is_square(mp_int *arg,int *ret)
42 {
43 int res;
44 mp_digit c;
45 mp_int t;
46 unsigned long r;
47
48 /* Default to Non-square :) */
49 *ret = MP_NO;
50
51 if (arg->sign == MP_NEG) {
52 return MP_VAL;
53 }
54
55 /* digits used? (TSD) */
56 if (arg->used == 0) {
57 return MP_OKAY;
58 }
59
60 /* First check mod 128 (suppose that DIGIT_BIT is at least 7) */
61 if (rem_128[127 & DIGIT(arg,0)] == 1) {
62 return MP_OKAY;
63 }
64
65 /* Next check mod 105 (3*5*7) */
66 if ((res = mp_mod_d(arg,105,&c)) != MP_OKAY) {
67 return res;
68 }
69 if (rem_105[c] == 1) {
70 return MP_OKAY;
71 }
72
73
74 if ((res = mp_init_set_int(&t,11L*13L*17L*19L*23L*29L*31L)) != MP_OKAY) {
75 return res;
76 }
77 if ((res = mp_mod(arg,&t,&t)) != MP_OKAY) {
78 goto ERR_;
79 }
80 r = mp_get_int(&t);
81 /* Check for other prime modules, note it's not an ERROR but we must
82 * free "t" so the easiest way is to goto ERR_. We know that res
83 * is already equal to MP_OKAY from the mp_mod call
84 */
85 if (((1L<<(r%11)) & 0x5C4L) != 0L) goto ERR_;
86 if (((1L<<(r%13)) & 0x9E4L) != 0L) goto ERR_;
87 if (((1L<<(r%17)) & 0x5CE8L) != 0L) goto ERR_;
88 if (((1L<<(r%19)) & 0x4F50CL) != 0L) goto ERR_;
89 if (((1L<<(r%23)) & 0x7ACCA0L) != 0L) goto ERR_;
90 if (((1L<<(r%29)) & 0xC2EDD0CL) != 0L) goto ERR_;
91 if (((1L<<(r%31)) & 0x6DE2B848L) != 0L) goto ERR_;
92
93 /* Final check - is sqr(sqrt(arg)) == arg ? */
94 if ((res = mp_sqrt(arg,&t)) != MP_OKAY) {
95 goto ERR_;
96 }
97 if ((res = mp_sqr(&t,&t)) != MP_OKAY) {
98 goto ERR_;
99 }
100
101 *ret = (mp_cmp_mag(&t,arg) == MP_EQ) ? MP_YES : MP_NO;
102 ERR_:mp_clear(&t);
103 return res;
104 }
105 #endif
106
107 /* $Source$ */
108 /* $Revision$ */
109 /* $Date$ */