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Diffstat (limited to 'gnu/lib/libgmp/mpn_rshift.c')
-rw-r--r-- | gnu/lib/libgmp/mpn_rshift.c | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/gnu/lib/libgmp/mpn_rshift.c b/gnu/lib/libgmp/mpn_rshift.c new file mode 100644 index 0000000..a4d00e8 --- /dev/null +++ b/gnu/lib/libgmp/mpn_rshift.c @@ -0,0 +1,90 @@ +/* mpn_rshift -- Shift right a low-level natural-number 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 "gmp-impl.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; +} |