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308 lines
6.7 KiB
308 lines
6.7 KiB
/* mpi-bit.c - MPI bit level functions |
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* Copyright (C) 1998, 1999 Free Software Foundation, Inc. |
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* |
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* This file is part of GnuPG. |
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* |
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* GnuPG is free software; you can redistribute it and/or modify |
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* it under the terms of the GNU General Public License as published by |
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* the Free Software Foundation; either version 2 of the License, or |
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* (at your option) any later version. |
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* |
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* GnuPG is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA |
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*/ |
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#include "mpi-internal.h" |
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#include "longlong.h" |
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#define A_LIMB_1 ((mpi_limb_t) 1) |
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/**************** |
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* Sometimes we have MSL (most significant limbs) which are 0; |
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* this is for some reasons not good, so this function removes them. |
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*/ |
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void mpi_normalize(MPI a) |
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{ |
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for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--) |
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; |
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} |
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EXPORT_SYMBOL_GPL(mpi_normalize); |
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/**************** |
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* Return the number of bits in A. |
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*/ |
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unsigned mpi_get_nbits(MPI a) |
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{ |
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unsigned n; |
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mpi_normalize(a); |
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if (a->nlimbs) { |
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mpi_limb_t alimb = a->d[a->nlimbs - 1]; |
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if (alimb) |
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n = count_leading_zeros(alimb); |
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else |
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n = BITS_PER_MPI_LIMB; |
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n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB; |
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} else |
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n = 0; |
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return n; |
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} |
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EXPORT_SYMBOL_GPL(mpi_get_nbits); |
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/**************** |
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* Test whether bit N is set. |
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*/ |
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int mpi_test_bit(MPI a, unsigned int n) |
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{ |
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unsigned int limbno, bitno; |
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mpi_limb_t limb; |
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limbno = n / BITS_PER_MPI_LIMB; |
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bitno = n % BITS_PER_MPI_LIMB; |
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if (limbno >= a->nlimbs) |
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return 0; /* too far left: this is a 0 */ |
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limb = a->d[limbno]; |
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return (limb & (A_LIMB_1 << bitno)) ? 1 : 0; |
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} |
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EXPORT_SYMBOL_GPL(mpi_test_bit); |
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/**************** |
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* Set bit N of A. |
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*/ |
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void mpi_set_bit(MPI a, unsigned int n) |
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{ |
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unsigned int i, limbno, bitno; |
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limbno = n / BITS_PER_MPI_LIMB; |
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bitno = n % BITS_PER_MPI_LIMB; |
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if (limbno >= a->nlimbs) { |
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for (i = a->nlimbs; i < a->alloced; i++) |
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a->d[i] = 0; |
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mpi_resize(a, limbno+1); |
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a->nlimbs = limbno+1; |
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} |
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a->d[limbno] |= (A_LIMB_1<<bitno); |
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} |
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/**************** |
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* Set bit N of A. and clear all bits above |
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*/ |
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void mpi_set_highbit(MPI a, unsigned int n) |
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{ |
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unsigned int i, limbno, bitno; |
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limbno = n / BITS_PER_MPI_LIMB; |
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bitno = n % BITS_PER_MPI_LIMB; |
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if (limbno >= a->nlimbs) { |
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for (i = a->nlimbs; i < a->alloced; i++) |
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a->d[i] = 0; |
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mpi_resize(a, limbno+1); |
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a->nlimbs = limbno+1; |
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} |
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a->d[limbno] |= (A_LIMB_1<<bitno); |
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for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++) |
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a->d[limbno] &= ~(A_LIMB_1 << bitno); |
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a->nlimbs = limbno+1; |
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} |
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EXPORT_SYMBOL_GPL(mpi_set_highbit); |
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/**************** |
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* clear bit N of A and all bits above |
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*/ |
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void mpi_clear_highbit(MPI a, unsigned int n) |
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{ |
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unsigned int limbno, bitno; |
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limbno = n / BITS_PER_MPI_LIMB; |
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bitno = n % BITS_PER_MPI_LIMB; |
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if (limbno >= a->nlimbs) |
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return; /* not allocated, therefore no need to clear bits :-) */ |
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for ( ; bitno < BITS_PER_MPI_LIMB; bitno++) |
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a->d[limbno] &= ~(A_LIMB_1 << bitno); |
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a->nlimbs = limbno+1; |
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} |
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/**************** |
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* Clear bit N of A. |
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*/ |
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void mpi_clear_bit(MPI a, unsigned int n) |
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{ |
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unsigned int limbno, bitno; |
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limbno = n / BITS_PER_MPI_LIMB; |
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bitno = n % BITS_PER_MPI_LIMB; |
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if (limbno >= a->nlimbs) |
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return; /* Don't need to clear this bit, it's far too left. */ |
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a->d[limbno] &= ~(A_LIMB_1 << bitno); |
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} |
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EXPORT_SYMBOL_GPL(mpi_clear_bit); |
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/**************** |
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* Shift A by COUNT limbs to the right |
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* This is used only within the MPI library |
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*/ |
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void mpi_rshift_limbs(MPI a, unsigned int count) |
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{ |
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mpi_ptr_t ap = a->d; |
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mpi_size_t n = a->nlimbs; |
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unsigned int i; |
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if (count >= n) { |
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a->nlimbs = 0; |
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return; |
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} |
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for (i = 0; i < n - count; i++) |
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ap[i] = ap[i+count]; |
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ap[i] = 0; |
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a->nlimbs -= count; |
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} |
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/* |
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* Shift A by N bits to the right. |
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*/ |
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void mpi_rshift(MPI x, MPI a, unsigned int n) |
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{ |
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mpi_size_t xsize; |
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unsigned int i; |
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unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); |
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unsigned int nbits = (n%BITS_PER_MPI_LIMB); |
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if (x == a) { |
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/* In-place operation. */ |
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if (nlimbs >= x->nlimbs) { |
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x->nlimbs = 0; |
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return; |
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} |
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if (nlimbs) { |
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for (i = 0; i < x->nlimbs - nlimbs; i++) |
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x->d[i] = x->d[i+nlimbs]; |
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x->d[i] = 0; |
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x->nlimbs -= nlimbs; |
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} |
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if (x->nlimbs && nbits) |
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mpihelp_rshift(x->d, x->d, x->nlimbs, nbits); |
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} else if (nlimbs) { |
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/* Copy and shift by more or equal bits than in a limb. */ |
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xsize = a->nlimbs; |
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x->sign = a->sign; |
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RESIZE_IF_NEEDED(x, xsize); |
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x->nlimbs = xsize; |
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for (i = 0; i < a->nlimbs; i++) |
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x->d[i] = a->d[i]; |
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x->nlimbs = i; |
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if (nlimbs >= x->nlimbs) { |
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x->nlimbs = 0; |
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return; |
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} |
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if (nlimbs) { |
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for (i = 0; i < x->nlimbs - nlimbs; i++) |
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x->d[i] = x->d[i+nlimbs]; |
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x->d[i] = 0; |
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x->nlimbs -= nlimbs; |
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} |
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if (x->nlimbs && nbits) |
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mpihelp_rshift(x->d, x->d, x->nlimbs, nbits); |
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} else { |
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/* Copy and shift by less than bits in a limb. */ |
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xsize = a->nlimbs; |
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x->sign = a->sign; |
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RESIZE_IF_NEEDED(x, xsize); |
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x->nlimbs = xsize; |
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if (xsize) { |
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if (nbits) |
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mpihelp_rshift(x->d, a->d, x->nlimbs, nbits); |
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else { |
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/* The rshift helper function is not specified for |
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* NBITS==0, thus we do a plain copy here. |
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*/ |
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for (i = 0; i < x->nlimbs; i++) |
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x->d[i] = a->d[i]; |
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} |
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} |
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} |
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MPN_NORMALIZE(x->d, x->nlimbs); |
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} |
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EXPORT_SYMBOL_GPL(mpi_rshift); |
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/**************** |
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* Shift A by COUNT limbs to the left |
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* This is used only within the MPI library |
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*/ |
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void mpi_lshift_limbs(MPI a, unsigned int count) |
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{ |
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mpi_ptr_t ap; |
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int n = a->nlimbs; |
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int i; |
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if (!count || !n) |
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return; |
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RESIZE_IF_NEEDED(a, n+count); |
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ap = a->d; |
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for (i = n-1; i >= 0; i--) |
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ap[i+count] = ap[i]; |
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for (i = 0; i < count; i++) |
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ap[i] = 0; |
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a->nlimbs += count; |
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} |
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/* |
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* Shift A by N bits to the left. |
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*/ |
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void mpi_lshift(MPI x, MPI a, unsigned int n) |
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{ |
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unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); |
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unsigned int nbits = (n%BITS_PER_MPI_LIMB); |
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if (x == a && !n) |
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return; /* In-place shift with an amount of zero. */ |
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if (x != a) { |
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/* Copy A to X. */ |
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unsigned int alimbs = a->nlimbs; |
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int asign = a->sign; |
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mpi_ptr_t xp, ap; |
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RESIZE_IF_NEEDED(x, alimbs+nlimbs+1); |
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xp = x->d; |
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ap = a->d; |
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MPN_COPY(xp, ap, alimbs); |
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x->nlimbs = alimbs; |
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x->flags = a->flags; |
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x->sign = asign; |
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} |
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if (nlimbs && !nbits) { |
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/* Shift a full number of limbs. */ |
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mpi_lshift_limbs(x, nlimbs); |
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} else if (n) { |
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/* We use a very dump approach: Shift left by the number of |
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* limbs plus one and than fix it up by an rshift. |
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*/ |
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mpi_lshift_limbs(x, nlimbs+1); |
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mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits); |
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} |
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MPN_NORMALIZE(x->d, x->nlimbs); |
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}
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