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Diffstat (limited to 'lib/mpi/mpi-scan.c')
| -rw-r--r-- | lib/mpi/mpi-scan.c | 136 |
1 files changed, 136 insertions, 0 deletions
diff --git a/lib/mpi/mpi-scan.c b/lib/mpi/mpi-scan.c new file mode 100644 index 0000000..b2da5ad --- /dev/null +++ b/lib/mpi/mpi-scan.c @@ -0,0 +1,136 @@ +/* mpi-scan.c - MPI functions + * Copyright (C) 1998, 1999, 2000, 2001 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" + +/**************** + * Scan through an mpi and return byte for byte. a -1 is returned to indicate + * the end of the mpi. Scanning is done from the lsb to the msb, returned + * values are in the range of 0 .. 255. + * + * FIXME: This code is VERY ugly! + */ +int mpi_getbyte(const MPI a, unsigned idx) +{ + int i, j; + unsigned n; + mpi_ptr_t ap; + mpi_limb_t limb; + + ap = a->d; + for (n = 0, i = 0; i < a->nlimbs; i++) { + limb = ap[i]; + for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++) + if (n == idx) + return (limb >> j * 8) & 0xff; + } + return -1; +} + +/**************** + * Put a value at position IDX into A. idx counts from lsb to msb + */ +void mpi_putbyte(MPI a, unsigned idx, int xc) +{ + int i, j; + unsigned n; + mpi_ptr_t ap; + mpi_limb_t limb, c; + + c = xc & 0xff; + ap = a->d; + for (n = 0, i = 0; i < a->alloced; i++) { + limb = ap[i]; + for (j = 0; j < BYTES_PER_MPI_LIMB; j++, n++) + if (n == idx) { +#if BYTES_PER_MPI_LIMB == 4 + if (j == 0) + limb = (limb & 0xffffff00) | c; + else if (j == 1) + limb = (limb & 0xffff00ff) | (c << 8); + else if (j == 2) + limb = (limb & 0xff00ffff) | (c << 16); + else + limb = (limb & 0x00ffffff) | (c << 24); +#elif BYTES_PER_MPI_LIMB == 8 + if (j == 0) + limb = (limb & 0xffffffffffffff00) | c; + else if (j == 1) + limb = + (limb & 0xffffffffffff00ff) | (c << + 8); + else if (j == 2) + limb = + (limb & 0xffffffffff00ffff) | (c << + 16); + else if (j == 3) + limb = + (limb & 0xffffffff00ffffff) | (c << + 24); + else if (j == 4) + limb = + (limb & 0xffffff00ffffffff) | (c << + 32); + else if (j == 5) + limb = + (limb & 0xffff00ffffffffff) | (c << + 40); + else if (j == 6) + limb = + (limb & 0xff00ffffffffffff) | (c << + 48); + else + limb = + (limb & 0x00ffffffffffffff) | (c << + 56); +#else +#error please enhance this function, its ugly - i know. +#endif + if (a->nlimbs <= i) + a->nlimbs = i + 1; + ap[i] = limb; + return; + } + } + log_bug("index out of range\n"); +} + +/**************** + * Count the number of zerobits at the low end of A + */ +unsigned mpi_trailing_zeros(const MPI a) +{ + unsigned n, count = 0; + + for (n = 0; n < a->nlimbs; n++) { + if (a->d[n]) { + unsigned nn; + mpi_limb_t alimb = a->d[n]; + + count_trailing_zeros(nn, alimb); + count += nn; + break; + } + count += BITS_PER_MPI_LIMB; + } + return count; + +} |