src/arith.c

   1 /* Arithmetic for numbers greater than a long int, for GNU tar.
   2    Copyright (C) 1996, 1997 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify it
   5    under the terms of the GNU General Public License as published by the
   6    Free Software Foundation; either version 2, or (at your option) any later
   7    version.
   8
   9    This program is distributed in the hope that it will be useful, but
  10    WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
  12    Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License along
  15    with this program; if not, write to the Free Software Foundation, Inc.,
  16    59 Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 #include "system.h"
  19
  20 /* common.h is needed to define FATAL_ERROR.  It also includes arith.h.  */
  21 #include "common.h"
  22
  23 /* GNU tar needs handling numbers exceeding 32 bits, which is the size of
  24    unsigned long ints for many C compilers.  This module should provide
  25    machinery for handling at least BITS_PER_TARLONG bits per number.  If
  26    `long long' ints are available and are sufficient for the task, they will
  27    be used preferrably.
  28
  29    Russell Cattelan reports 165 Gb single tapes (digital video D2 tapes on
  30    Ampex drives), so requiring 38 bits for the tape length in bytes.  He
  31    also reports breaking the terabyte limit with a single file (using SGI
  32    xFS file system over 37 28GB disk arrays attached to a Power Challenge
  33    XL; check out http://www.lcse.umn.edu/ for a picture), so requiring a
  34    little more than 40 bits for the file size in bytes.  The POSIX header
  35    structure allows for 12 octal digits to represent file lengths, that is,
  36    up to 36 bits for the byte size of files.
  37
  38    If `long long' is not supported by the compiler, SIZEOF_LONG_LONG will be
  39    set to zero by configure.  In this case, or if `long long' ints does not
  40    have enough bits, then huge numbers are rather represented by an array of
  41    longs, with the least significant super-digit at position 0.  For making
  42    multiplication and decimal input/output easy, the base of a super-digit
  43    is an exact exponent of 10, and is such that base*base fits in a long.  */
  44
  45 #if SUPERDIGIT
  46
  47 /*-------------------------------.
  48 | Check if ACCUMULATOR is zero.  |
  49 `-------------------------------*/
  50
  51 int
  52 zerop_tarlong_helper (unsigned long *accumulator)
  53 {
  54   int counter;
  55
  56   for (counter = LONGS_PER_TARLONG - 1; counter >= 0; counter--)
  57     if (accumulator[counter])
  58       return 0;
  59
  60   return 1;
  61 }
  62
  63 /*----------------------------------------------.
  64 | Check if FIRST is strictly less than SECOND.  |
  65 `----------------------------------------------*/
  66
  67 int
  68 lessp_tarlong_helper (unsigned long *first, unsigned long *second)
  69 {
  70   int counter;
  71
  72   for (counter = LONGS_PER_TARLONG - 1; counter >= 0; counter--)
  73     if (first[counter] != second[counter])
  74       return first[counter] < second[counter];
  75
  76   return 0;
  77 }
  78
  79 /*----------------------------.
  80 | Reset ACCUMULATOR to zero.  |
  81 `----------------------------*/
  82
  83 void
  84 clear_tarlong_helper (unsigned long *accumulator)
  85 {
  86   int counter;
  87
  88   for (counter = 0; counter < LONGS_PER_TARLONG; counter++)
  89     accumulator[counter] = 0;
  90 }
  91
  92 /*----------------------------.
  93 | To ACCUMULATOR, add VALUE.  |
  94 `----------------------------*/
  95
  96 void
  97 add_to_tarlong_helper (unsigned long *accumulator, int value)
  98 {
  99   int counter;
 100
 101   if (value < 0)
 102     for (counter = 0; counter < LONGS_PER_TARLONG; counter++)
 103       {
 104         if (accumulator[counter] >= -value)
 105           {
 106             accumulator[counter] += value;
 107             return;
 108           }
 109         accumulator[counter] += value + SUPERDIGIT;
 110         value = -1;
 111       }
 112   else
 113     for (counter = 0; counter < LONGS_PER_TARLONG; counter++)
 114       {
 115         if (accumulator[counter] + value < SUPERDIGIT)
 116           {
 117             accumulator[counter] += value;
 118             return;
 119           }
 120         accumulator[counter] += value - SUPERDIGIT;
 121         value = 1;
 122       }
 123   FATAL_ERROR ((0, 0, _("Arithmetic overflow")));
 124 }
 125
 126 /*--------------------------------.
 127 | Multiply ACCUMULATOR by VALUE.  |
 128 `--------------------------------*/
 129
 130 void
 131 mult_tarlong_helper (unsigned long *accumulator, int value)
 132 {
 133   int carry = 0;
 134   int counter;
 135
 136   for (counter = 0; counter < LONGS_PER_TARLONG; counter++)
 137     {
 138       carry += accumulator[counter] * value;
 139       accumulator[counter] = carry % SUPERDIGIT;
 140       carry /= SUPERDIGIT;
 141     }
 142   if (carry)
 143     FATAL_ERROR ((0, 0, _("Arithmetic overflow")));
 144 }
 145
 146 /*----------------------------------------------------------.
 147 | Print the decimal representation of ACCUMULATOR on FILE.  |
 148 `----------------------------------------------------------*/
 149
 150 void
 151 print_tarlong_helper (unsigned long *accumulator, FILE *file)
 152 {
 153   int counter = LONGS_PER_TARLONG - 1;
 154
 155   while (counter > 0 && accumulator[counter] == 0)
 156     counter--;
 157
 158   fprintf (file, "%uld", accumulator[counter]);
 159   while (counter > 0)
 160     fprintf (file, TARLONG_FORMAT, accumulator[--counter]);
 161 }
 162
 163 #endif /* SUPERDIGIT */