Mercurial > dropbear
annotate libtommath/bn_mp_sub_d.c @ 323:3bfbe95f9a14
Add -P pidfile patch from Swen Schillig
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 07 Jun 2006 14:10:21 +0000 |
parents | eed26cff980b |
children | 5ff8218bcee9 |
rev | line source |
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284
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1 #include <tommath.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 * The library is free for all purposes without any express |
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13 * guarantee it works. |
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14 * |
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.org |
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16 */ |
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17 |
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18 /* single digit subtraction */ |
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19 int |
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20 mp_sub_d (mp_int * a, mp_digit b, mp_int * c) |
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21 { |
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22 mp_digit *tmpa, *tmpc, mu; |
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23 int res, ix, oldused; |
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24 |
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25 /* grow c as required */ |
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26 if (c->alloc < a->used + 1) { |
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27 if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) { |
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28 return res; |
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29 } |
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30 } |
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31 |
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32 /* if a is negative just do an unsigned |
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33 * addition [with fudged signs] |
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34 */ |
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35 if (a->sign == MP_NEG) { |
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36 a->sign = MP_ZPOS; |
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37 res = mp_add_d(a, b, c); |
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38 a->sign = c->sign = MP_NEG; |
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39 return res; |
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40 } |
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41 |
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42 /* setup regs */ |
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43 oldused = c->used; |
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44 tmpa = a->dp; |
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45 tmpc = c->dp; |
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46 |
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47 /* if a <= b simply fix the single digit */ |
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48 if ((a->used == 1 && a->dp[0] <= b) || a->used == 0) { |
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49 if (a->used == 1) { |
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50 *tmpc++ = b - *tmpa; |
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51 } else { |
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52 *tmpc++ = b; |
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53 } |
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54 ix = 1; |
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55 |
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56 /* negative/1digit */ |
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57 c->sign = MP_NEG; |
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58 c->used = 1; |
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59 } else { |
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60 /* positive/size */ |
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61 c->sign = MP_ZPOS; |
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62 c->used = a->used; |
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63 |
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64 /* subtract first digit */ |
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65 *tmpc = *tmpa++ - b; |
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66 mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1); |
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67 *tmpc++ &= MP_MASK; |
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68 |
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69 /* handle rest of the digits */ |
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70 for (ix = 1; ix < a->used; ix++) { |
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71 *tmpc = *tmpa++ - mu; |
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72 mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1); |
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73 *tmpc++ &= MP_MASK; |
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74 } |
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75 } |
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76 |
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77 /* zero excess digits */ |
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78 while (ix++ < oldused) { |
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79 *tmpc++ = 0; |
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80 } |
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81 mp_clamp(c); |
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82 return MP_OKAY; |
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83 } |
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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
parents:
diff
changeset
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84 |
eed26cff980b
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
parents:
diff
changeset
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85 #endif |