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annotate libtommath/bn_mp_expt_d_ex.c @ 1640:228b086794b7
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| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Thu, 21 Mar 2019 00:09:07 +0800 |
| parents | 8bba51a55704 |
| children | f52919ffd3b1 |
| rev | line source |
|---|---|
| 1436 | 1 #include <tommath_private.h> |
| 2 #ifdef BN_MP_EXPT_D_EX_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, [email protected], http://libtom.org | |
| 16 */ | |
| 17 | |
| 18 /* calculate c = a**b using a square-multiply algorithm */ | |
| 19 int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast) | |
| 20 { | |
| 21 int res; | |
| 22 unsigned int x; | |
| 23 | |
| 24 mp_int g; | |
| 25 | |
| 26 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { | |
| 27 return res; | |
| 28 } | |
| 29 | |
| 30 /* set initial result */ | |
| 31 mp_set (c, 1); | |
| 32 | |
| 33 if (fast != 0) { | |
| 34 while (b > 0) { | |
| 35 /* if the bit is set multiply */ | |
| 36 if ((b & 1) != 0) { | |
| 37 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { | |
| 38 mp_clear (&g); | |
| 39 return res; | |
| 40 } | |
| 41 } | |
| 42 | |
| 43 /* square */ | |
| 44 if (b > 1) { | |
| 45 if ((res = mp_sqr (&g, &g)) != MP_OKAY) { | |
| 46 mp_clear (&g); | |
| 47 return res; | |
| 48 } | |
| 49 } | |
| 50 | |
| 51 /* shift to next bit */ | |
| 52 b >>= 1; | |
| 53 } | |
| 54 } | |
| 55 else { | |
| 56 for (x = 0; x < DIGIT_BIT; x++) { | |
| 57 /* square */ | |
| 58 if ((res = mp_sqr (c, c)) != MP_OKAY) { | |
| 59 mp_clear (&g); | |
| 60 return res; | |
| 61 } | |
| 62 | |
| 63 /* if the bit is set multiply */ | |
| 64 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { | |
| 65 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { | |
| 66 mp_clear (&g); | |
| 67 return res; | |
| 68 } | |
| 69 } | |
| 70 | |
| 71 /* shift to next bit */ | |
| 72 b <<= 1; | |
| 73 } | |
| 74 } /* if ... else */ | |
| 75 | |
| 76 mp_clear (&g); | |
| 77 return MP_OKAY; | |
| 78 } | |
| 79 #endif | |
| 80 | |
|
1470
8bba51a55704
Update to libtommath v1.0.1
Matt Johnston <matt@ucc.asn.au>
parents:
1436
diff
changeset
|
81 /* ref: $Format:%D$ */ |
|
8bba51a55704
Update to libtommath v1.0.1
Matt Johnston <matt@ucc.asn.au>
parents:
1436
diff
changeset
|
82 /* git commit: $Format:%H$ */ |
|
8bba51a55704
Update to libtommath v1.0.1
Matt Johnston <matt@ucc.asn.au>
parents:
1436
diff
changeset
|
83 /* commit time: $Format:%ai$ */ |