/* 
    Copyright (C) 2009, 2011 William Hart

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 2.1 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "gmp.h"
#include "flint.h"
#include "fft.h"
      
void fft_truncate1(mp_limb_t ** ii, mp_size_t n, flint_bitcnt_t w, 
                   mp_limb_t ** t1, mp_limb_t ** t2, mp_size_t trunc)
{
    mp_size_t i;
    mp_size_t limbs = (w*n)/FLINT_BITS;
   
    if (trunc == 2*n)
        fft_radix2(ii, n, w, t1, t2);
    else if (trunc <= n)
    {
        for (i = 0; i < n; i++)
            mpn_add_n(ii[i], ii[i], ii[i+n], limbs + 1);
      
        fft_truncate1(ii, n/2, 2*w, t1, t2, trunc);
    } else
    {
        for (i = 0; i < n; i++) 
        {   
            fft_butterfly(*t1, *t2, ii[i], ii[n+i], i, limbs, w);
   
            SWAP_PTRS(ii[i],   *t1);
            SWAP_PTRS(ii[n+i], *t2);
        }

        fft_radix2(ii, n/2, 2*w, t1, t2);
        fft_truncate1(ii+n, n/2, 2*w, t1, t2, trunc - n);
   }
}

void fft_truncate(mp_limb_t ** ii,  mp_size_t n, flint_bitcnt_t w, 
                  mp_limb_t ** t1, mp_limb_t ** t2, mp_size_t trunc)
{
    mp_size_t i;
    mp_size_t limbs = (w*n)/FLINT_BITS;
   
    if (trunc == 2*n)
       fft_radix2(ii, n, w, t1, t2);
    else if (trunc <= n)
       fft_truncate(ii, n/2, 2*w, t1, t2, trunc);
    else
    {
        for (i = 0; i < trunc - n; i++) 
        {   
            fft_butterfly(*t1, *t2, ii[i], ii[n+i], i, limbs, w);
   
            SWAP_PTRS(ii[i],   *t1);
            SWAP_PTRS(ii[n+i], *t2);
        }

        for ( ; i < n; i++)
            fft_adjust(ii[i+n], ii[i], i, limbs, w); 
   
        fft_radix2(ii, n/2, 2*w, t1, t2);
        fft_truncate1(ii+n, n/2, 2*w, t1, t2, trunc - n);
   }
}