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127 lines
3.4 KiB
C
127 lines
3.4 KiB
C
/* sqrt.c: bcmath library file. */
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/*
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Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc.
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Copyright (C) 2000 Philip A. Nelson
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details. (LICENSE)
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to:
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The Free Software Foundation, Inc.
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59 Temple Place, Suite 330
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Boston, MA 02111-1307 USA.
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You may contact the author by:
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e-mail: philnelson@acm.org
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us-mail: Philip A. Nelson
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Computer Science Department, 9062
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Western Washington University
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Bellingham, WA 98226-9062
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*************************************************************************/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <ctype.h>
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#include <stdarg.h>
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#include "bcmath.h"
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#include "private.h"
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/* Take the square root NUM and return it in NUM with SCALE digits
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after the decimal place. */
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int
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bc_sqrt (bc_num *num, int scale)
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{
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int rscale, cmp_res, done;
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int cscale;
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bc_num guess, guess1, point5, diff;
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/* Initial checks. */
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cmp_res = bc_compare (*num, BCG(_zero_));
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if (cmp_res < 0)
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return 0; /* error */
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else
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{
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if (cmp_res == 0)
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{
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bc_free_num (num);
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*num = bc_copy_num (BCG(_zero_));
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return 1;
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}
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}
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cmp_res = bc_compare (*num, BCG(_one_));
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if (cmp_res == 0)
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{
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bc_free_num (num);
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*num = bc_copy_num (BCG(_one_));
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return 1;
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}
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/* Initialize the variables. */
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rscale = MAX (scale, (*num)->n_scale);
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bc_init_num(&guess1);
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bc_init_num(&diff);
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point5 = bc_new_num (1,1);
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point5->n_value[1] = 5;
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/* Calculate the initial guess. */
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if (cmp_res < 0)
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{
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/* The number is between 0 and 1. Guess should start at 1. */
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guess = bc_copy_num (BCG(_one_));
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cscale = (*num)->n_scale;
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}
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else
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{
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/* The number is greater than 1. Guess should start at 10^(exp/2). */
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bc_init_num(&guess);
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bc_int2num (&guess,10);
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bc_int2num (&guess1,(*num)->n_len);
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bc_multiply (guess1, point5, &guess1, 0);
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guess1->n_scale = 0;
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bc_raise (guess, guess1, &guess, 0);
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bc_free_num (&guess1);
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cscale = 3;
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}
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/* Find the square root using Newton's algorithm. */
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done = FALSE;
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while (!done)
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{
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bc_free_num (&guess1);
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guess1 = bc_copy_num (guess);
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bc_divide (*num, guess, &guess, cscale);
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bc_add (guess, guess1, &guess, 0);
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bc_multiply (guess, point5, &guess, cscale);
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bc_sub (guess, guess1, &diff, cscale+1);
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if (bc_is_near_zero (diff, cscale))
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{
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if (cscale < rscale+1)
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cscale = MIN (cscale*3, rscale+1);
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else
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done = TRUE;
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}
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}
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/* Assign the number and clean up. */
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bc_free_num (num);
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bc_divide (guess,BCG(_one_),num,rscale);
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bc_free_num (&guess);
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bc_free_num (&guess1);
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bc_free_num (&point5);
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bc_free_num (&diff);
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return 1;
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}
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