Mercurial > dropbear
annotate libtommath/bn_mp_sub_d.c @ 1687:f8d8af12ac14
Make "dbclient -m help -c help" work
author | Matt Johnston <matt@ucc.asn.au> |
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date | Tue, 26 May 2020 20:15:39 +0800 |
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1 #include "tommath_private.h" |
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2 #ifdef BN_MP_SUB_D_C |
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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4 * |
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5 * LibTomMath is a library that provides multiple-precision |
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6 * integer arithmetic as well as number theoretic functionality. |
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7 * |
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8 * The library was designed directly after the MPI library by |
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9 * Michael Fromberger but has been written from scratch with |
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10 * additional optimizations in place. |
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11 * |
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12 * SPDX-License-Identifier: Unlicense |
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13 */ |
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14 |
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15 /* single digit subtraction */ |
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16 int mp_sub_d(const mp_int *a, mp_digit b, mp_int *c) |
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17 { |
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18 mp_digit *tmpa, *tmpc, mu; |
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19 int res, ix, oldused; |
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20 |
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21 /* grow c as required */ |
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22 if (c->alloc < (a->used + 1)) { |
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23 if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) { |
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24 return res; |
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25 } |
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26 } |
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27 |
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28 /* if a is negative just do an unsigned |
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29 * addition [with fudged signs] |
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30 */ |
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31 if (a->sign == MP_NEG) { |
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32 mp_int a_ = *a; |
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33 a_.sign = MP_ZPOS; |
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34 res = mp_add_d(&a_, b, c); |
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35 c->sign = MP_NEG; |
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36 |
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37 /* clamp */ |
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38 mp_clamp(c); |
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39 |
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40 return res; |
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41 } |
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42 |
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43 /* setup regs */ |
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44 oldused = c->used; |
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45 tmpa = a->dp; |
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46 tmpc = c->dp; |
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47 |
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48 /* if a <= b simply fix the single digit */ |
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49 if (((a->used == 1) && (a->dp[0] <= b)) || (a->used == 0)) { |
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50 if (a->used == 1) { |
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51 *tmpc++ = b - *tmpa; |
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52 } else { |
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53 *tmpc++ = b; |
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54 } |
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55 ix = 1; |
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56 |
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57 /* negative/1digit */ |
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58 c->sign = MP_NEG; |
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59 c->used = 1; |
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60 } else { |
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61 /* positive/size */ |
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62 c->sign = MP_ZPOS; |
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63 c->used = a->used; |
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64 |
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65 /* subtract first digit */ |
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66 *tmpc = *tmpa++ - b; |
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67 mu = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u); |
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68 *tmpc++ &= MP_MASK; |
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69 |
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70 /* handle rest of the digits */ |
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71 for (ix = 1; ix < a->used; ix++) { |
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72 *tmpc = *tmpa++ - mu; |
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73 mu = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u); |
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74 *tmpc++ &= MP_MASK; |
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75 } |
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76 } |
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77 |
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78 /* zero excess digits */ |
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79 while (ix++ < oldused) { |
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80 *tmpc++ = 0; |
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81 } |
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82 mp_clamp(c); |
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83 return MP_OKAY; |
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84 } |
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85 |
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86 #endif |
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87 |
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88 /* ref: HEAD -> master, tag: v1.1.0 */ |
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89 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ |
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update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
Steffen Jaeckel <s_jaeckel@gmx.de>
parents:
1470
diff
changeset
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90 /* commit time: 2019-01-28 20:32:32 +0100 */ |