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/*
** SWISH++
** enc_int.c
**
** Copyright (C) 2003 Paul J. Lucas
**
** This program 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.
**
** This program 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
// standard
#include <iostream>
// local
#include "enc_int.h"
#include "platform.h"
using namespace std;
//*****************************************************************************
//
// SYNOPSIS
//
int dec_int( register unsigned char const *&p )
//
// DESCRIPTION
//
// Decode an integer from an encoded byte sequence. See the comment for
// enc_int() for details of the encoding scheme.
//
// PARAMETERS
//
// p A pointer to the start of the encoded integer. After an integer is
// decoded, it is left one past the last byte.
//
// RETURN VALUE
//
// The integer.
//
//*****************************************************************************
{
register unsigned n = 0;
do {
n = (n << 7) | (*p & 0x7Fu);
} while ( *p++ & 0x80u );
return n;
}
//*****************************************************************************
//
// SYNOPSIS
//
ostream& enc_int( ostream &o, register unsigned n )
//
// DESCRIPTION
//
// Write an unsigned integer to the given ostream in an encoded format.
// The format uses a varying number of bytes. For a given byte, only the
// lower 7 bits are used for data; the high bit, if set, is used to
// indicate whether the integer continues into the next byte. The encoded
// integer is written to the given ostream starting with the most
// significant byte.
//
// PARAMETERS
//
// o The ostream to write to.
//
// n The integer to be written.
//
// RETURN VALUE
//
// Returns the passed-in ostream.
//
//*****************************************************************************
{
unsigned char buf[ 20 ];
//
// Encode the integer (in reverse because it's easier) just like atoi().
//
register unsigned char *p = buf + sizeof buf;
do {
*--p = 0x80u | (n & 0x7Fu);
} while ( n >>= 7 );
buf[ sizeof buf - 1 ] &= 0x7Fu; // clear last "continuation bit"
return o.write( reinterpret_cast<char*>( p ), buf + sizeof buf - p );
}
/* vim:set et sw=4 ts=4: */
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