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annotate tomsfastmath/src/bit/fp_div_2d.c @ 643:a362b62d38b2 dropbear-tfm

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Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a with Makefile.in renamed
author Matt Johnston <matt@ucc.asn.au>
date Wed, 23 Nov 2011 18:10:20 +0700
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a362b62d38b2 Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a
Matt Johnston <matt@ucc.asn.au>
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1 /* TomsFastMath, a fast ISO C bignum library.
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2 *
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3 * This project is meant to fill in where LibTomMath
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4 * falls short. That is speed ;-)
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5 *
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6 * This project is public domain and free for all purposes.
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7 *
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8 * Tom St Denis, [email protected]
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9 */
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10 #include <tfm.h>
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12 /* c = a / 2**b */
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13 void fp_div_2d(fp_int *a, int b, fp_int *c, fp_int *d)
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14 {
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15 fp_digit D, r, rr;
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16 int x;
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17 fp_int t;
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19 /* if the shift count is <= 0 then we do no work */
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20 if (b <= 0) {
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21 fp_copy (a, c);
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22 if (d != NULL) {
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23 fp_zero (d);
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24 }
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25 return;
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26 }
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28 fp_init(&t);
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29
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30 /* get the remainder */
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31 if (d != NULL) {
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32 fp_mod_2d (a, b, &t);
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33 }
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35 /* copy */
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36 fp_copy(a, c);
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38 /* shift by as many digits in the bit count */
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39 if (b >= (int)DIGIT_BIT) {
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40 fp_rshd (c, b / DIGIT_BIT);
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41 }
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43 /* shift any bit count < DIGIT_BIT */
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44 D = (fp_digit) (b % DIGIT_BIT);
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45 if (D != 0) {
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46 register fp_digit *tmpc, mask, shift;
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48 /* mask */
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49 mask = (((fp_digit)1) << D) - 1;
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51 /* shift for lsb */
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52 shift = DIGIT_BIT - D;
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54 /* alias */
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55 tmpc = c->dp + (c->used - 1);
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57 /* carry */
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58 r = 0;
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59 for (x = c->used - 1; x >= 0; x--) {
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60 /* get the lower bits of this word in a temp */
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61 rr = *tmpc & mask;
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63 /* shift the current word and mix in the carry bits from the previous word */
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64 *tmpc = (*tmpc >> D) | (r << shift);
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65 --tmpc;
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66
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67 /* set the carry to the carry bits of the current word found above */
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68 r = rr;
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69 }
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70 }
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71 fp_clamp (c);
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72 if (d != NULL) {
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73 fp_copy (&t, d);
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74 }
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75 }
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76
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77 /* $Source$ */
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78 /* $Revision$ */
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79 /* $Date$ */