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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 ;
}