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php5  5.3.10
Functions
sqrt.c File Reference
#include <config.h>
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdarg.h>
#include "bcmath.h"
#include "private.h"

Go to the source code of this file.

Functions

int bc_sqrt (bc_num *num, int scale TSRMLS_DC)

Function Documentation

int bc_sqrt ( bc_num num,
int scale  TSRMLS_DC 
)

Definition at line 45 of file sqrt.c.

{
  int rscale, cmp_res, done;
  int cscale;
  bc_num guess, guess1, point5, diff;

  /* Initial checks. */
  cmp_res = bc_compare (*num, BCG(_zero_));
  if (cmp_res < 0)
    return 0;        /* error */
  else
    {
      if (cmp_res == 0)
       {
         bc_free_num (num);
         *num = bc_copy_num (BCG(_zero_));
         return 1;
       }
    }
  cmp_res = bc_compare (*num, BCG(_one_));
  if (cmp_res == 0)
    {
      bc_free_num (num);
      *num = bc_copy_num (BCG(_one_));
      return 1;
    }

  /* Initialize the variables. */
  rscale = MAX (scale, (*num)->n_scale);
  bc_init_num(&guess TSRMLS_CC);
  bc_init_num(&guess1 TSRMLS_CC);
  bc_init_num(&diff TSRMLS_CC);
  point5 = bc_new_num (1,1);
  point5->n_value[1] = 5;


  /* Calculate the initial guess. */
  if (cmp_res < 0)
    {
      /* The number is between 0 and 1.  Guess should start at 1. */
      guess = bc_copy_num (BCG(_one_));
      cscale = (*num)->n_scale;
    }
  else
    {
      /* The number is greater than 1.  Guess should start at 10^(exp/2). */
      bc_int2num (&guess,10);

      bc_int2num (&guess1,(*num)->n_len);
      bc_multiply (guess1, point5, &guess1, 0 TSRMLS_CC);
      guess1->n_scale = 0;
      bc_raise (guess, guess1, &guess, 0 TSRMLS_CC);
      bc_free_num (&guess1);
      cscale = 3;
    }

  /* Find the square root using Newton's algorithm. */
  done = FALSE;
  while (!done)
    {
      bc_free_num (&guess1);
      guess1 = bc_copy_num (guess);
      bc_divide (*num, guess, &guess, cscale TSRMLS_CC);
      bc_add (guess, guess1, &guess, 0);
      bc_multiply (guess, point5, &guess, cscale TSRMLS_CC);
      bc_sub (guess, guess1, &diff, cscale+1);
      if (bc_is_near_zero (diff, cscale))
       {
         if (cscale < rscale+1)
           cscale = MIN (cscale*3, rscale+1);
         else
           done = TRUE;
       }
    }

  /* Assign the number and clean up. */
  bc_free_num (num);
  bc_divide (guess,BCG(_one_),num,rscale TSRMLS_CC);
  bc_free_num (&guess);
  bc_free_num (&guess1);
  bc_free_num (&point5);
  bc_free_num (&diff);
  return 1;
}

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