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-rw-r--r--lib/mpi/mpi-bit.c308
1 files changed, 308 insertions, 0 deletions
diff --git a/lib/mpi/mpi-bit.c b/lib/mpi/mpi-bit.c
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+/* mpi-bit.c - MPI bit level functions
+ * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG 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 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "mpi-internal.h"
+#include "longlong.h"
+
+#define A_LIMB_1 ((mpi_limb_t) 1)
+
+/****************
+ * Sometimes we have MSL (most significant limbs) which are 0;
+ * this is for some reasons not good, so this function removes them.
+ */
+void mpi_normalize(MPI a)
+{
+ for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
+ ;
+}
+EXPORT_SYMBOL_GPL(mpi_normalize);
+
+/****************
+ * Return the number of bits in A.
+ */
+unsigned mpi_get_nbits(MPI a)
+{
+ unsigned n;
+
+ mpi_normalize(a);
+
+ if (a->nlimbs) {
+ mpi_limb_t alimb = a->d[a->nlimbs - 1];
+ if (alimb)
+ n = count_leading_zeros(alimb);
+ else
+ n = BITS_PER_MPI_LIMB;
+ n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
+ } else
+ n = 0;
+ return n;
+}
+EXPORT_SYMBOL_GPL(mpi_get_nbits);
+
+/****************
+ * Test whether bit N is set.
+ */
+int mpi_test_bit(MPI a, unsigned int n)
+{
+ unsigned int limbno, bitno;
+ mpi_limb_t limb;
+
+ limbno = n / BITS_PER_MPI_LIMB;
+ bitno = n % BITS_PER_MPI_LIMB;
+
+ if (limbno >= a->nlimbs)
+ return 0; /* too far left: this is a 0 */
+ limb = a->d[limbno];
+ return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
+}
+EXPORT_SYMBOL_GPL(mpi_test_bit);
+
+/****************
+ * Set bit N of A.
+ */
+void mpi_set_bit(MPI a, unsigned int n)
+{
+ unsigned int i, limbno, bitno;
+
+ limbno = n / BITS_PER_MPI_LIMB;
+ bitno = n % BITS_PER_MPI_LIMB;
+
+ if (limbno >= a->nlimbs) {
+ for (i = a->nlimbs; i < a->alloced; i++)
+ a->d[i] = 0;
+ mpi_resize(a, limbno+1);
+ a->nlimbs = limbno+1;
+ }
+ a->d[limbno] |= (A_LIMB_1<<bitno);
+}
+
+/****************
+ * Set bit N of A. and clear all bits above
+ */
+void mpi_set_highbit(MPI a, unsigned int n)
+{
+ unsigned int i, limbno, bitno;
+
+ limbno = n / BITS_PER_MPI_LIMB;
+ bitno = n % BITS_PER_MPI_LIMB;
+
+ if (limbno >= a->nlimbs) {
+ for (i = a->nlimbs; i < a->alloced; i++)
+ a->d[i] = 0;
+ mpi_resize(a, limbno+1);
+ a->nlimbs = limbno+1;
+ }
+ a->d[limbno] |= (A_LIMB_1<<bitno);
+ for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
+ a->d[limbno] &= ~(A_LIMB_1 << bitno);
+ a->nlimbs = limbno+1;
+}
+EXPORT_SYMBOL_GPL(mpi_set_highbit);
+
+/****************
+ * clear bit N of A and all bits above
+ */
+void mpi_clear_highbit(MPI a, unsigned int n)
+{
+ unsigned int limbno, bitno;
+
+ limbno = n / BITS_PER_MPI_LIMB;
+ bitno = n % BITS_PER_MPI_LIMB;
+
+ if (limbno >= a->nlimbs)
+ return; /* not allocated, therefore no need to clear bits :-) */
+
+ for ( ; bitno < BITS_PER_MPI_LIMB; bitno++)
+ a->d[limbno] &= ~(A_LIMB_1 << bitno);
+ a->nlimbs = limbno+1;
+}
+
+/****************
+ * Clear bit N of A.
+ */
+void mpi_clear_bit(MPI a, unsigned int n)
+{
+ unsigned int limbno, bitno;
+
+ limbno = n / BITS_PER_MPI_LIMB;
+ bitno = n % BITS_PER_MPI_LIMB;
+
+ if (limbno >= a->nlimbs)
+ return; /* Don't need to clear this bit, it's far too left. */
+ a->d[limbno] &= ~(A_LIMB_1 << bitno);
+}
+EXPORT_SYMBOL_GPL(mpi_clear_bit);
+
+
+/****************
+ * Shift A by COUNT limbs to the right
+ * This is used only within the MPI library
+ */
+void mpi_rshift_limbs(MPI a, unsigned int count)
+{
+ mpi_ptr_t ap = a->d;
+ mpi_size_t n = a->nlimbs;
+ unsigned int i;
+
+ if (count >= n) {
+ a->nlimbs = 0;
+ return;
+ }
+
+ for (i = 0; i < n - count; i++)
+ ap[i] = ap[i+count];
+ ap[i] = 0;
+ a->nlimbs -= count;
+}
+
+/*
+ * Shift A by N bits to the right.
+ */
+void mpi_rshift(MPI x, MPI a, unsigned int n)
+{
+ mpi_size_t xsize;
+ unsigned int i;
+ unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
+ unsigned int nbits = (n%BITS_PER_MPI_LIMB);
+
+ if (x == a) {
+ /* In-place operation. */
+ if (nlimbs >= x->nlimbs) {
+ x->nlimbs = 0;
+ return;
+ }
+
+ if (nlimbs) {
+ for (i = 0; i < x->nlimbs - nlimbs; i++)
+ x->d[i] = x->d[i+nlimbs];
+ x->d[i] = 0;
+ x->nlimbs -= nlimbs;
+ }
+ if (x->nlimbs && nbits)
+ mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
+ } else if (nlimbs) {
+ /* Copy and shift by more or equal bits than in a limb. */
+ xsize = a->nlimbs;
+ x->sign = a->sign;
+ RESIZE_IF_NEEDED(x, xsize);
+ x->nlimbs = xsize;
+ for (i = 0; i < a->nlimbs; i++)
+ x->d[i] = a->d[i];
+ x->nlimbs = i;
+
+ if (nlimbs >= x->nlimbs) {
+ x->nlimbs = 0;
+ return;
+ }
+
+ if (nlimbs) {
+ for (i = 0; i < x->nlimbs - nlimbs; i++)
+ x->d[i] = x->d[i+nlimbs];
+ x->d[i] = 0;
+ x->nlimbs -= nlimbs;
+ }
+
+ if (x->nlimbs && nbits)
+ mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
+ } else {
+ /* Copy and shift by less than bits in a limb. */
+ xsize = a->nlimbs;
+ x->sign = a->sign;
+ RESIZE_IF_NEEDED(x, xsize);
+ x->nlimbs = xsize;
+
+ if (xsize) {
+ if (nbits)
+ mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
+ else {
+ /* The rshift helper function is not specified for
+ * NBITS==0, thus we do a plain copy here.
+ */
+ for (i = 0; i < x->nlimbs; i++)
+ x->d[i] = a->d[i];
+ }
+ }
+ }
+ MPN_NORMALIZE(x->d, x->nlimbs);
+}
+EXPORT_SYMBOL_GPL(mpi_rshift);
+
+/****************
+ * Shift A by COUNT limbs to the left
+ * This is used only within the MPI library
+ */
+void mpi_lshift_limbs(MPI a, unsigned int count)
+{
+ mpi_ptr_t ap;
+ int n = a->nlimbs;
+ int i;
+
+ if (!count || !n)
+ return;
+
+ RESIZE_IF_NEEDED(a, n+count);
+
+ ap = a->d;
+ for (i = n-1; i >= 0; i--)
+ ap[i+count] = ap[i];
+ for (i = 0; i < count; i++)
+ ap[i] = 0;
+ a->nlimbs += count;
+}
+
+/*
+ * Shift A by N bits to the left.
+ */
+void mpi_lshift(MPI x, MPI a, unsigned int n)
+{
+ unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
+ unsigned int nbits = (n%BITS_PER_MPI_LIMB);
+
+ if (x == a && !n)
+ return; /* In-place shift with an amount of zero. */
+
+ if (x != a) {
+ /* Copy A to X. */
+ unsigned int alimbs = a->nlimbs;
+ int asign = a->sign;
+ mpi_ptr_t xp, ap;
+
+ RESIZE_IF_NEEDED(x, alimbs+nlimbs+1);
+ xp = x->d;
+ ap = a->d;
+ MPN_COPY(xp, ap, alimbs);
+ x->nlimbs = alimbs;
+ x->flags = a->flags;
+ x->sign = asign;
+ }
+
+ if (nlimbs && !nbits) {
+ /* Shift a full number of limbs. */
+ mpi_lshift_limbs(x, nlimbs);
+ } else if (n) {
+ /* We use a very dump approach: Shift left by the number of
+ * limbs plus one and than fix it up by an rshift.
+ */
+ mpi_lshift_limbs(x, nlimbs+1);
+ mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits);
+ }
+
+ MPN_NORMALIZE(x->d, x->nlimbs);
+}
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