/*  slftancf.cpp  by K.Tsuru  */
// function ID 4104 DRADIX
/*********************************************
SLong class
It makes a table of tangent coefficients T[n]
using the combination number combL().
T[0] = 0, T[n] = Tn (n>0)
**********************************************/
#ifndef SN_H
#include "sn.h"
#endif

static SNBlock<SLong>* T = NULL;    //It keeps the result of calculation.
static uint upto = 0;       //How many terms have been calculated ? Tn(upto) ok

void TanCoeffFree(){
    if(upto == 0) return;
    T->size(0,-1);  T = NULL;   upto = 0;
}

SLong TanCoeff(uint m){
    if(!upto){  //first call
        T = new SNBlock<SLong>(minArraySize);
        (*T)[0].SetSmall(1);        upto = 1;
    }
    if(!m){ //free memory
        TanCoeffFree();
        return 0.0;
    } else if(m <= upto) return (*T)[m-1];  //  T(m) = T[m-1]  m-1 <= upto

    uint j, n;
    SLong sum, f;
    if(T->reserve(m) == 0) f.SetError(f.OUT_OF_RANGE,"TanCoeff", 4104);
//cout << "m= " << m << " T->size() = " << T->size()<< endl;
    for(n = 1; n < m ; n++){
          sum.SetSmall((n & 1) ? -1 : 1);
          for(j = 1; j <= n ; j++){
             f = combL(2*n+1, 2*j)*(*T)[n-j];
             if(j & 1) sum += f;
             else      sum -= f;
          }
          (*T)[n] = sum;
    }
    upto = m;
    return (*T)[m-1];
}