bitfiddle.h

chm阅读器 用于在linux系统下chm文档的阅读

/*

  Copyright (C) 2003  Razvan Cojocaru <[e-mail]>
  Most of the code in this file is a modified version of code from
  Pabs' GPL chmdeco project, credits and thanks go to him.
 
  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.

*/


#define UINT16ARRAY(x) ((unsigned char)(x)[0] | ((u_int16_t)(x)[1] << 8))
#define UINT32ARRAY(x) (UINT16ARRAY(x) | ((u_int32_t)(x)[2] << 16) \
		| ((u_int32_t)(x)[3] << 24))

inline unsigned int get_int32_le( void *addr)
{
	unsigned char *p = (unsigned char*) addr;
	return (unsigned int) ( p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24) );
}


inline u_int64_t be_encint(unsigned char* buffer, size_t& length)
{
	u_int64_t result = 0;
	int shift=0;
	length = 0;

	do {
		result |= ((*buffer) & 0x7f) << shift;
		shift += 7;
		++length;

	} while (*(buffer++) & 0x80);
	
	return result;
}


/* 
   Finds the first unset bit in memory. Returns the number of set bits found.
   Returns -1 if the buffer runs out before we find an unset bit.
*/
inline int ffus(unsigned char* byte, int* bit, size_t& length)
{
	int bits = 0;
	length = 0;

	while(*byte & (1 << *bit)){
		if(*bit) 
			--(*bit);
		else { 
			++byte;
			++length;
			*bit = 7; 
		}
		++bits;
	}

	if(*bit) 
		--(*bit);
	else { 
		++length;
		*bit = 7; 
	}
	
	return bits;
}


inline u_int64_t sr_int(unsigned char* byte, int* bit,
			unsigned char s, unsigned char r, size_t& length)
{
	u_int64_t ret; 
	unsigned char mask;
	int n, n_bits, num_bits, base, count;
	length = 0;
	size_t fflen;

	if(!bit || *bit > 7 || s != 2)
		return ~(u_int64_t)0;
	ret = 0;

	count = ffus(byte, bit, fflen);
	length += fflen;
	byte += length;

	n_bits = n = r + (count ? count-1 : 0) ;

	while(n > 0) {
		num_bits = n > *bit ? *bit : n-1;
		base = n > *bit ? 0 : *bit - (n-1);
		
		switch(num_bits){
			case 0: 
				mask = 1; 
				break;
			case 1: 
				mask = 3; 
				break;
			case 2: 
				mask = 7; 
				break;
			case 3: 
				mask = 0xf; 
				break;
			case 4: 
				mask = 0x1f; 
				break;
			case 5: 
				mask = 0x3f; 
				break;
			case 6: 
				mask = 0x7f; 
				break;
			case 7: 
				mask = 0xff; 
				break;
                        default:
                                mask = 0xff;
				break;
		}

		mask <<= base;
		ret = (ret << (num_bits+1)) | 
			(u_int64_t)((*byte & mask) >> base);
		
		if( n > *bit ){
			++byte;
			++length;
			n -= *bit+1;
			*bit = 7;
		} else {
			*bit -= n;
			n = 0;
		}
	}

	if(count) 
		ret |= (u_int64_t)1 << n_bits;

	return ret;
}