/* Copyright (c) 1993 Association of Universities for Research
 * in Astronomy. All rights reserved. Produced under National
 * Aeronautics and Space Administration Contract No. NAS5-26555.
 */
/* BIT INPUT ROUTINES */

/*
 * Modified by R. White, 16 June 1992, to handle VMS fixed-length records
 */

#include <stdio.h>
#include "qfile.h"

/* THE BIT BUFFER */

static int buffer;                  /* Bits waiting to be input             */
static int bits_to_go;              /* Number of bits still in buffer       */


/* INITIALIZE BIT INPUT */

extern void
start_inputing_bits()
{
    /*
     * Buffer starts out with no bits in it
     */
    bits_to_go = 0;
}


/* INPUT A BIT */

extern int
input_bit(infile)
QFILE *infile;
{
    /* Read the next byte if no bits are left in buffer  */
    if (bits_to_go == 0) {
        buffer = qgetc(infile);
        if (buffer == EOF) {
            /*
             * end of file is an error for this application
             */
            fprintf(stderr, "input_bit: unexpected end-of-file\n");
            exit(-1);
        }
        bits_to_go = 8;
    }
    /*
     * Return the next bit
     */
    bits_to_go -= 1;
    return((buffer>>bits_to_go) & 1);
}


/* INPUT N BITS (N must be <= 8) */

extern int
input_nbits(infile,n)
QFILE *infile;
int n;
{
int c;

    if (bits_to_go < n) {
        /*
         * need another byte's worth of bits
         */
        buffer <<= 8;
        c = qgetc(infile);
        if (c == EOF) {
            /*
             * end of file is an error for this application
             */
            fprintf(stderr, "input_nbits: unexpected end-of-file\n");
            exit(-1);
        }
        buffer |= c;
        bits_to_go += 8;
    }
    /*
     * now pick off the first n bits
     */
    bits_to_go -= n;
    return( (buffer>>bits_to_go) & ((1<<n)-1) );
}