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/*

    		 Crown Copyright (c) 1997

    This TenDRA(r) Computer Program is subject to Copyright

    owned by the United Kingdom Secretary of State for Defence

    acting through the Defence Evaluation and Research Agency

    (DERA).  It is made available to Recipients with a

    royalty-free licence for its use, reproduction, transfer

    to other parties and amendment for any purpose not excluding

    product development provided that any such use et cetera

    shall be deemed to be acceptance of the following conditions:-

        (1) Its Recipients shall ensure that this Notice is

        reproduced upon any copies or amended versions of it;

        (2) Any amended version of it shall be clearly marked to

        show both the nature of and the organisation responsible

        for the relevant amendment or amendments;

        (3) Its onward transfer from a recipient to another

        party shall be deemed to be that party's acceptance of

        these conditions;

        (4) DERA gives no warranty or assurance as to its

        quality or suitability for any purpose and DERA accepts

        no liability whatsoever in relation to any use to which

        it may be put.

*/

#include "config.h"

#include "c_types.h"

#include "error.h"

#include "buffer.h"

#include "char.h"

#include "decode.h"

#include "encode.h"

#include "file.h"

#include "literal.h"

/*

    FILL A BITSTREAM

    This routine fills the bitstream bs from its associated file.  It

    returns the number of bytes read.

*/

static unsigned fill_bitstream

    PROTO_N ( ( bs ) )

    PROTO_T ( BITSTREAM *bs )

{

    unsigned sz ;

    FILE *f = bs->file ;

    string text = bs->text ;

    sz = ( unsigned ) fread ( ( gen_ptr ) text, sizeof ( character ),

			      ( size_t ) CHUNK_SIZE, f ) ;

    if ( sz == 0 ) {

	/* No more characters in file */

	bs->link = ( gen_ptr ) text ;

	while ( sz < CHUNK_SIZE ) {

	    /* Fill buffer with all ones */

	    text [ sz ] = ( character ) BYTE_MASK ;

	    sz++ ;

	}

    }

    bs->size = sz ;

    return ( sz ) ;

}

/*

    CHECK FOR END OF FILE

    This routine checks whether the end of the file associated with the

    bitstream bs has been precisely reached.  Note that the link field

    is set to a non-null value by fill_bitstream if the end of file is

    encountered.

*/

int de_eof

    PROTO_N ( ( bs ) )

    PROTO_T ( BITSTREAM *bs )

{

    if ( bs->link ) return ( 0 ) ;

    if ( bs->bytes >= bs->size ) {

	IGNORE fill_bitstream ( bs ) ;

	if ( bs->link ) return ( 1 ) ;

    }

    return ( 0 ) ;

}

/*

    TABLE OF BIT MASKS

    This array gives the bit masks for values up to 16 bits.

*/

static unsigned long bit_mask [17] = {

    0x0000,

#if FS_NUMBER_SUFFIX

    0x0001UL, 0x0003UL, 0x0007UL, 0x000fUL,

    0x001fUL, 0x003fUL, 0x007fUL, 0x00ffUL,

    0x01ffUL, 0x03ffUL, 0x07ffUL, 0x0fffUL,

    0x1fffUL, 0x3fffUL, 0x7fffUL, 0xffffUL

#else

    0x0001, 0x0003, 0x0007, 0x000f,

    0x001f, 0x003f, 0x007f, 0x00ff,

    0x01ff, 0x03ff, 0x07ff, 0x0fff,

    0x1fff, 0x3fff, 0x7fff, 0xffff

#endif

} ;

/*

    READ A NUMBER OF BITS FROM A BITSTREAM

    This routine reads the next n bits from the bitstream bs.  n will be

    at most 16.

*/

unsigned de_bits

    PROTO_N ( ( bs, n ) )

    PROTO_T ( BITSTREAM *bs X unsigned n )

{

    unsigned long d = 0 ;

    string text = bs->text ;

    unsigned sz = bs->size ;

    unsigned bytes = bs->bytes ;

    unsigned bits = 0 ;

    /* Build up result */

    unsigned m = n + bs->bits ;

    while ( m ) {

	unsigned b ;

	unsigned long c ;

	/* Refill buffer from file if necessary */

	if ( bytes >= sz ) {

	    sz = fill_bitstream ( bs ) ;

	    bytes = 0 ;

	    bits = 0 ;

	}

	/* Get next character */

	c = ( unsigned long ) text [ bytes ] ;

	d = ( ( d << BYTE_SIZE ) | c ) ;

	b = BYTE_SIZE - bits ;

	if ( m < b ) {

	    d >>= ( b - m ) ;

	    bits += m ;

	    m = 0 ;

	} else {

	    bits += b ;

	    m -= b ;

	}

	if ( bits == BYTE_SIZE ) {

	    bits = 0 ;

	    bytes++ ;

	}

    }

    bs->bytes = bytes ;

    bs->bits = bits ;

    d &= bit_mask [n] ;

    return ( ( unsigned ) d ) ;

}

/*

    READ A LARGE NUMBER OF BITS FROM A BITSTREAM

    This routine is identical to de_bits except that it works for up to

    32 bits.

*/

unsigned long de_long_bits

    PROTO_N ( ( bs, n ) )

    PROTO_T ( BITSTREAM *bs X unsigned n )

{

    unsigned long a, b ;

    if ( n > 16 ) {

	a = ( unsigned long ) de_bits ( bs, n - 16 ) ;

	n = 16 ;

    } else {

	a = 0 ;

    }

    b = ( unsigned long ) de_bits ( bs, n ) ;

    return ( ( a << 16 ) | b ) ;

}

/*

    READ AN INTEGER FROM A BITSTREAM

    This routine reads an integer as a series of octal digits from the

    bitstream bs.

*/

unsigned long de_int

    PROTO_N ( ( bs ) )

    PROTO_T ( BITSTREAM *bs )

{

    unsigned long d, n = 0 ;

    for ( ; ; ) {

	d = ( unsigned long ) de_bits ( bs, ( unsigned ) 4 ) ;

	if ( d & 0x8 ) break ;

	n = ( ( n << 3 ) | d ) ;

    }

    n = ( ( n << 3 ) | ( d & 0x7 ) ) ;

    return ( n ) ;

}

/*

    ALIGN A BITSTREAM TO A BYTE BOUNDARY

    This routine reads enough bits from the bitstream bs to align it to

    the next byte boundary.

*/

void de_boundary

    PROTO_N ( ( bs ) )

    PROTO_T ( BITSTREAM *bs )

{

    unsigned bits = bs->bits ;

    if ( bits ) IGNORE de_bits ( bs, BYTE_SIZE - bits ) ;

    return ;

}

/*

    READ A STRING FROM A BITSTREAM

    This routine reads a string from the bitstream bs into the buffer bf.

*/

void de_tdfstring

    PROTO_N ( ( bs, bf ) )

    PROTO_T ( BITSTREAM *bs X BUFFER *bf )

{

    unsigned m = ( unsigned ) de_int ( bs ) ;

    unsigned long n = de_int ( bs ) ;

    string p = stretch_buffer ( bf, bf->posn, ( gen_size ) n ) ;

    bf->posn = p + n ;

    while ( n ) {

	int ch = CHAR_SIMPLE ;

	unsigned long c = ( unsigned long ) de_bits ( bs, m ) ;

	c = from_ascii ( c, &ch ) ;

	*( p++ ) = ( character ) c ;

	n-- ;

    }

    *p = 0 ;

    return ;

}