fileb.h

/* fileb.h - write/read files bit by bit
 * 
 * MIT License
 *
 * Copyright (c) 2016 Paulo André Azevedo Quirino
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * [email protected] 
 */

#ifndef FILEB_H
#define FILEB_H

#include <stdio.h>

typedef struct bCursor {
	unsigned char d;
	size_t s;
} bitCursor;

/* creates a new bitCursor object with default values
 * (needed for starting bit-wise read/write operations,
 * a pointer to that same cursor must then be provided
 * to subsequent read/write operations until all data is
 * read/written)
 *
 * @returns cursor with default values
 */
bitCursor newBitCursor() {
	bitCursor c = {0, 0};
	return c;
}

#define curBusySpace c->s
#define curData c->d

/* Writes a number of bits into a file
 *
 * @param ptr a pointer to the variable containing the data to be written
 * @param sizeb the number of bits to be written
 * @param rSizeb the real size of the variable in bits
 * @param fp a pointer to the file
 * @param c a pointer to a bitCursor (possibly containing bits from the last variable written)
 */
void fwriteb(void *restrict ptr, size_t sizeb, size_t rSizeb, FILE *fp, bitCursor *c) {

	size_t firstRelevantBit = rSizeb - sizeb,
				 firstRelevantByte = firstRelevantBit / 8,
				 distanceToStartOfByte = firstRelevantBit - firstRelevantByte * 8;

	unsigned char *pchar = (unsigned char*)ptr + firstRelevantByte;	// Assuming little Endian

	size_t bitsToWrite = sizeb,
				 bitsToAdd;

readywrite:
	bitsToAdd = 8 - (curBusySpace > distanceToStartOfByte ? curBusySpace : distanceToStartOfByte);

	curData |= (*pchar << distanceToStartOfByte) >> curBusySpace;

	curBusySpace += bitsToAdd;
	if (curBusySpace >= 8) {
		fwrite(&curData, 1, 1, fp);
		curBusySpace = curData = 0;
	}

	bitsToWrite -= bitsToAdd;
	if (bitsToWrite <= 0) return;

	distanceToStartOfByte += bitsToAdd;

	if (distanceToStartOfByte >= 8) {
		distanceToStartOfByte = 0;
		pchar++;
	}

	goto readywrite;
}


/* Writes the remaining bits after a sequence of fwriteb operations
 * (required for correct behaviour)
 *
 * @param fp a pointer to the file
 * @param c a pointer to a bitCursor (possibly containing bits from the last variable written)
 */
void fcloseb(FILE *fp, bitCursor *c) {
	if (curBusySpace <= 0) return;
	fwrite(&curData, 1, 1, fp);
}

/* Reads a number of bits from a file (it is your responsibility to init the var as 0)
 *
 * @param ptr a pointer to the variable in which to write data that is read
 * @param sizeb the number of bits to be read
 * @param rSizeb the real size of the variable in bits
 * @param fp a pointer to the file
 * @param c a pointer to a bitCursor (possibly containing bits from the last read Byte)
 */
void freadb(void *restrict ptr, size_t sizeb, size_t rSizeb, FILE *fp, bitCursor *c) {

	size_t firstRelevantBit = rSizeb - sizeb,
				 firstRelevantByte = firstRelevantBit / 8,
				 distanceToStartOfByte = firstRelevantBit - firstRelevantByte*8;

	unsigned char *pchar = (unsigned char*)ptr + firstRelevantByte;

	size_t bitsToRead = sizeb,
				 bitsToAdd,
				 availableBits = 8 - distanceToStartOfByte;

readyread:
	if (curBusySpace <= 0) {
		fread(&curData, 1, 1, fp);
		curBusySpace = 8;
	}

	bitsToAdd = curBusySpace > availableBits ? availableBits : curBusySpace;
	(*pchar) |= curData >> distanceToStartOfByte;

	curData <<= bitsToAdd;
	curBusySpace -= bitsToAdd;
	bitsToRead -= bitsToAdd;
	if (bitsToRead <= 0) return;

	distanceToStartOfByte += bitsToAdd;
	if (distanceToStartOfByte >= 8) {
		distanceToStartOfByte = 0;
		pchar++;
	}
	availableBits = 8 - distanceToStartOfByte;

	goto readyread;
}

#endif