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/* $Id: cursor.cpp,v 1.3 2006/11/05 04:42:43 ganzhorn Exp $
* This file is part of lfhex.
* Copyright (C) 2006 Salem Ganzhorn <eyekode@yahoo.com>
*
* 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 version 2.
*
* 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include "local.h"
#include "cursor.hpp"
//
// Cursor implimentation
//
Cursor::Cursor(off_t byteOffset,
off_t charOffset,
off_t low,
off_t high,
off_t charsPerByte)
: _byteOffset(byteOffset),
_charOffset(charOffset),
_low(low),
_high(high),
_charsPerByte(charsPerByte)
{}
// note: range includes low but excludes high: [low,high) (like stl)
// note: [foo,foo) is considered the empty set
bool Cursor::setRange( off_t low, off_t high )
{
if ( low > high )
return false;
_low = low;
_high = high;
return true;
}
off_t Cursor::decrByByte( off_t n )
{
// check for underflow
if (n > _byteOffset)
return OutOfRange;
else
_byteOffset -= n;
return _byteOffset;
}
off_t Cursor::decrByChar( off_t n )
{
off_t byteDelta = n/_charsPerByte;
off_t charDelta = n%_charsPerByte;
if ( charDelta > _charOffset ) {
if( byteDelta == MAX_OFFSET ) {
throw out_of_range("Cursor decriment underflowed.\n");
}
byteDelta++;
}
// if underflow.. then just return
if( byteDelta && OutOfRange == decrByByte( byteDelta ) ) {
return _charOffset;
}
if ( charDelta > _charOffset ) {
// offset == maxidx - abs(_charOffset - charDelta)
_charOffset = (_charsPerByte) - (charDelta - _charOffset);
} else {
_charOffset -= charDelta;
}
return _charOffset;
}
// note: off_t is always positive
off_t Cursor::incrByChar( off_t n )
{
off_t byteDelta = n/_charsPerByte;
off_t charDelta = n%_charsPerByte;
// carry
if ( charDelta + _charOffset >= _charsPerByte ) {
// Note: this cannot overflow unless chars perbyte == 1
if ( byteDelta == MAX_OFFSET ) {
throw out_of_range("Cursor increment exceeded maximum offset.\n");
}
byteDelta++;
}
// if out of range, just leave the char offset where it is
if( byteDelta && OutOfRange == incrByByte( byteDelta ) ) {
return _charOffset;
}
// limit _charOffset to _charsPerByte - 1
_charOffset = (charDelta + _charOffset)%_charsPerByte;
return _charOffset;
}
off_t Cursor::incrByByte( off_t byteDelta )
{
if ( byteDelta > MAX_OFFSET - _byteOffset ) {
throw out_of_range("Cursor increment exceeded maximum offset.\n");
}
if ( _byteOffset + byteDelta >= _high )
return OutOfRange;
return (_byteOffset += byteDelta);
}
//
// accessor implimentations
//
off_t Cursor::byteOffset() const
{
return _byteOffset;
}
off_t Cursor::charOffset() const
{
return _charOffset;
}
#define MIN(a,b) (a < b)?a:b
off_t Cursor::setCharsPerByte( off_t charsPerByte )
{
_charsPerByte = charsPerByte;
_charOffset = MIN(_charOffset,charsPerByte-1);
return _charsPerByte;
}
// _byteOffset values are clamped to:
// [_low,_high)
// _charOffset values are clamped to:
// [0,_charsPerByte-1]
void Cursor::setOffset( off_t byteOffset, off_t charOffset )
{
assignClamped(_byteOffset,byteOffset,0,_high);
assignClamped(_charOffset,charOffset,0,_charsPerByte);
}
off_t Cursor::charOffsetAbsolute() const
{
return _byteOffset*_charsPerByte + _charOffset;
}
//
// void Cursor::assignClamped(dst,src, low,high);
// convienience function for assigning dst = src
// clamped to [low,high)
//
void Cursor::assignClamped(off_t& dst, off_t src, off_t low, off_t high)
{
if( src < low ) {
dst = low;
} else if( src >= high ) {
dst = high-1;
} else {
dst = src;
}
}
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