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