91 lines
2.2 KiB
C
91 lines
2.2 KiB
C

/* mpn_rshift  Shift right a lowlevel naturalnumber integer.






Copyright (C) 1991 Free Software Foundation, Inc.






This file is part of the GNU MP Library.






The GNU MP Library is free software; you can redistribute it and/or modify



it under the terms of the GNU General Public License as published by



the Free Software Foundation; either version 2, or (at your option)



any later version.






The GNU MP Library is distributed in the hope that it will be useful,



but WITHOUT ANY WARRANTY; without even the implied warranty of



MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the



GNU General Public License for more details.






You should have received a copy of the GNU General Public License



along with the GNU MP Library; see the file COPYING. If not, write to



the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */






#include "gmp.h"



#include "gmpimpl.h"






/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right



and store the USIZE least significant limbs of the result at WP.



Return the size of the result.






Argument constraints:



0. U must be normalized (i.e. it's most significant limb != 0).



1. 0 <= CNT < BITS_PER_MP_LIMB



2. If the result is to be written over the input, WP must be <= UP.



*/






mp_size



#ifdef __STDC__



mpn_rshift (mp_ptr wp,



mp_srcptr up, mp_size usize,



unsigned cnt)



#else



mpn_rshift (wp, up, usize, cnt)



mp_ptr wp;



mp_srcptr up;



mp_size usize;



unsigned cnt;



#endif



{



mp_limb high_limb, low_limb;



unsigned sh_1, sh_2;



mp_size i;






if (usize == 0)



return 0;






sh_1 = cnt;



if (sh_1 == 0)



{



if (wp != up)



{



/* Copy from low end to high end, to allow specified input/output



overlapping. */



for (i = 0; i < usize; i++)



wp[i] = up[i];



}



return usize;



}






wp = 1;



sh_2 = BITS_PER_MP_LIMB  sh_1;



high_limb = up[0];



#if 0



if (cy_limb != NULL)



*cy_limb = high_limb << sh_2;



#endif



low_limb = high_limb;






for (i = 1; i < usize; i++)



{



high_limb = up[i];



wp[i] = (low_limb >> sh_1)  (high_limb << sh_2);



low_limb = high_limb;



}



low_limb >>= sh_1;



if (low_limb != 0)



{



wp[i] = low_limb;



return usize;



}






return usize  1;



}
