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;


}
