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lib/mpi/mpi-scan.c
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/* 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 "); } /**************** * 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; } |