/*  snfagrup.cpp  by K.Tsuru  */
// function ID = 1000  DRADIX
#ifndef SN_H
#include "sn.h"
#endif
/***************************************************************
Comparing two values from the position of one, return how many digits
agree each other.In the case of SDouble the exponent is not considerd
and the head zeros are not counted.
If an error ocuured return a negative value as follows.
not DRADIX           : -1
different type       : -2
not in standard form : -3
*****************************************************************/
long AgreeUpTo(const SNumber& a, const SNumber& b){
    if( !a.Sign(1000) && !b.Sign(1000) ) return 1;
    if( (a.Radix() != DRADIX) || (b.Radix() != DRADIX) ) return -1;
    if( a.Type() != b.Type() ) return -2;
    if( (a.Type() == a.REAL) && (!a[1] || !b[1]) ) return -3;

    uint top = min(a.Head(), b.Head()) +1, j = 0;
    int  at = 0, bt = 0, f, add = 0;
    long same;

    while( (j < top) && (a[j] == b[j]) ) j++;
    same = (long)j*DFIGURES;
    if(j < top){
        at = (int)a[j];     bt = (int)b[j];
    }

    if(a.Type() == a.REAL){
        add = -2*(int)DFIGURES; // 0.dddd
        if( j > 1 ) add += iFigures(a[1]);  //a(1) == b(1), a[1]=0123, b[1]=0123, add+=3
                                            //It excludes five zeros in 0000.0, add=-5.
        if(at && bt){
            fType r = DRADIX/10;
        //agreeing digits in the last figure
        //at = 1230, bt = 1256 -> 1 == 1, 2 == 2, 3 != 5 : add += 2
            while(r && ( (at/r) == (bt/r) ) ){  r /= 10;    add++;  }
        }
    } else if(at && bt){
        //agreeing digits in the tail of top figure
        f = abs( at - bt );     // xx00  :number of zeros agree. 5634-1234=4400, add+=2
        while( f && !(f%10) ){  f /= 10;    add++;  }
    }
    same += add;
    return same > 0 ? same : 0;
}