io.c

Lossless Data Compression Toolkit Version 1.1 of the lossless data compression toolkit by Nico deVri

/***********************************************************
	io.c -- input/output
***********************************************************/
#include "ar.h"
#include <stdlib.h>
#include <stdarg.h>

#define CRCPOLY  0xA001  /* ANSI CRC-16 */
                         /* CCITT: 0x8408 */
#define UPDATE_CRC(c) \
	crc = crctable[(crc ^ (c)) & 0xFF] ^ (crc >> CHAR_BIT)

FILE *arcfile, *infile, *outfile;
uint crc, bitbuf;

static ushort crctable[UCHAR_MAX + 1];
static uint  subbitbuf;
static int   bitcount;

void error(char *fmt, ...)
{
	va_list args;

	va_start(args, fmt);
	putc('\n', stderr);
	vfprintf(stderr, fmt, args);
	putc('\n', stderr);
	va_end(args);
	exit(EXIT_FAILURE);
}

void make_crctable(void)
{
	uint i, j, r;

	for (i = 0; i <= UCHAR_MAX; i++) {
		r = i;
		for (j = 0; j < CHAR_BIT; j++)
			if (r & 1) r = (r >> 1) ^ CRCPOLY;
			else       r >>= 1;
		crctable[i] = r;
	}
}

void fillbuf(int n)  /* Shift bitbuf n bits left, read n bits */
{
	bitbuf <<= n;
	while (n > bitcount) {
		bitbuf |= subbitbuf << (n -= bitcount);
		if (compsize != 0) {
			compsize--;  subbitbuf = (uchar) getc(arcfile);
		} else subbitbuf = 0;
		bitcount = CHAR_BIT;
	}
	bitbuf |= subbitbuf >> (bitcount -= n);
}

uint getbits(int n)
{
	uint x;

	x = bitbuf >> (BITBUFSIZ - n);  fillbuf(n);
	return x;
}

void putbits(int n, uint x)  /* Write rightmost n bits of x */
{
	if (n < bitcount) {
		subbitbuf |= x << (bitcount -= n);
	} else {
		if (compsize < origsize) {
			putc(subbitbuf | (x >> (n -= bitcount)), outfile);
			compsize++;
		} else unpackable = 1;
		if (n < CHAR_BIT) {
			subbitbuf = x << (bitcount = CHAR_BIT - n);
		} else {
			if (compsize < origsize) {
				putc(x >> (n - CHAR_BIT), outfile);
				compsize++;
			} else unpackable = 1;
			subbitbuf = x << (bitcount = 2 * CHAR_BIT - n);
		}
	}
}

int fread_crc(uchar *p, int n, FILE *f)
{
	int i;

	i = n = fread(p, 1, n, f);  origsize += n;
	while (--i >= 0) UPDATE_CRC(*p++);
	return n;
}

void fwrite_crc(uchar *p, int n, FILE *f)
{
	if (fwrite(p, 1, n, f) < n) error("Unable to write");
	while (--n >= 0) UPDATE_CRC(*p++);
}

void init_getbits(void)
{
	bitbuf = 0;  subbitbuf = 0;  bitcount = 0;
	fillbuf(BITBUFSIZ);
}

void init_putbits(void)
{
	bitcount = CHAR_BIT;  subbitbuf = 0;
}