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Diffstat (limited to 'sysdeps/generic/lshift.c')
-rw-r--r-- | sysdeps/generic/lshift.c | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/sysdeps/generic/lshift.c b/sysdeps/generic/lshift.c new file mode 100644 index 0000000..0b58389 --- /dev/null +++ b/sysdeps/generic/lshift.c @@ -0,0 +1,87 @@ +/* mpn_lshift -- Shift left low level. + +Copyright (C) 1991, 1993, 1994, 1996 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 Lesser General Public License as published by +the Free Software Foundation; either version 2.1 of the License, 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 Lesser General Public +License for more details. + +You should have received a copy of the GNU Lesser General Public License +along with the GNU MP Library; see the file COPYING.LIB. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +MA 02111-1307, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" + +/* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left + and store the USIZE least significant digits of the result at WP. + Return the bits shifted out from the most significant digit. + + Argument constraints: + 1. 0 < CNT < BITS_PER_MP_LIMB + 2. If the result is to be written over the input, WP must be >= UP. +*/ + +mp_limb_t +#if __STDC__ +mpn_lshift (register mp_ptr wp, + register mp_srcptr up, mp_size_t usize, + register unsigned int cnt) +#else +mpn_lshift (wp, up, usize, cnt) + register mp_ptr wp; + register mp_srcptr up; + mp_size_t usize; + register unsigned int cnt; +#endif +{ + register mp_limb_t high_limb, low_limb; + register unsigned sh_1, sh_2; + register mp_size_t i; + mp_limb_t retval; + +#ifdef DEBUG + if (usize == 0 || cnt == 0) + abort (); +#endif + + sh_1 = cnt; +#if 0 + if (sh_1 == 0) + { + if (wp != up) + { + /* Copy from high end to low end, to allow specified input/output + overlapping. */ + for (i = usize - 1; i >= 0; i--) + wp[i] = up[i]; + } + return 0; + } +#endif + + wp += 1; + sh_2 = BITS_PER_MP_LIMB - sh_1; + i = usize - 1; + low_limb = up[i]; + retval = low_limb >> sh_2; + high_limb = low_limb; + while (--i >= 0) + { + low_limb = up[i]; + wp[i] = (high_limb << sh_1) | (low_limb >> sh_2); + high_limb = low_limb; + } + wp[i] = high_limb << sh_1; + + return retval; +} |