/*
 * gunzip_mod.c -- Decompressing module for VME bootstrap
 *
 * Copyright (c) 1997 by Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
 *
 * Modified by Nick Holgate to suit VME Linux/m68k TFTP Loader
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 */

#include "defs.h"

/*
 * gzip declarations
 */

#define OF(args)  args

#define memzero(s, n)     mem_clear ((s), (n))

typedef unsigned char  uch;
typedef unsigned short ush;
typedef unsigned long  ulg;

#define INBUFSIZ	(32*1024)	/* input buffer size; for optimum performance*/
								/* the same or a multiple of other buffer	*/
								/* sizes, and memory_mod uses 32k			*/
#define WSIZE		(32*1024)	/* window size--must be a power of two, and */
								/* at least 32K for zip's deflate method	*/
#define CHANGING_WINDOW			/* this tells inflate.c that 'window' can	*/
								/* change in flush_window(), and that the	*/
								/* previous window (needed to copy data) is	*/
								/* preserved in 'previous_window'			*/

/***************************** Prototypes *****************************/

static int gunzip_open( void *data, long count );
static long gunzip_fillbuf( void *buf );
static int gunzip_close( void );
static int call_gunzip( void );
static void gzip_mark( void **ptr );
static void gzip_release( void **ptr );
static int fill_inbuf( void );
static void flush_window( void );
static void error( char *x );

/************************* End of Prototypes **************************/

MODULE gunzip_mod = {
	"gunzip",					/* name */
	WSIZE,						/* max. 512 bytes per TFTP packet */
	gunzip_open,
	gunzip_fillbuf,
	NULL,						/* cannot skip */
	gunzip_close,
	MOD_REST_INIT
};

/* special stack for gunzip() function */
static char *gunzip_stack;
/* some globals for storing values between stack switches */
static long gunzip_sp, gunzip_jumpback, main_sp, main_fp;
/* size of stack for gunzip(); 4k should be more than enough. (I guess 2k
 * would suffice also, but I don't want to track down stack overflows...) */
#define GUNZIP_STACK_SIZE	(4*1024)

static uch *inbuf;
static uch *window;
static uch *previous_window;

static unsigned insize = 0;  /* valid bytes in inbuf */
static unsigned inptr = 0;   /* index of next byte to be processed in inbuf */
static unsigned outcnt = 0;  /* bytes in output buffer */
static int exit_code = 0;
static long bytes_out = 0;
static int made_crc_table = 0;

#define get_byte()  (inptr < insize ? inbuf[inptr++] : fill_inbuf())

/* Diagnostic functions (stubbed out) */
#define Assert(cond,msg)
#define Trace(x)
#define Tracev(x)
#define Tracevv(x)
#define Tracec(c,x)
#define Tracecv(c,x)

#define STATIC static

#ifdef DEBUG_GUNZIP
FILE *xfile;
#endif

#include "inflate.c"

static int gunzip_open( void *data, long count )
{
	int rv;
	unsigned char buf[2];
	
	insize    = 0;  /* valid bytes in inbuf */
	inptr     = 0;  /* index of next byte to be processed in inbuf */
	outcnt    = 0;  /* bytes in output buffer */
	exit_code = 0;
	bytes_out = 0;
	crc       = (ulg)0xffffffffL; /* shift register contents */
	if (!made_crc_table)
	{
		++made_crc_table;
		makecrc();
	}

	/* try opening downstream channel */
	if (sopen( data, count ) < 0)
		return( -1 );

	/* check if data is gzipped */
	rv = sread( buf, 2 );
	sseek( 0, SEEK_SET );
	if (rv < 2) {
		printf( "File shorter than 2 bytes, can't test for gzip\n" );
		return( -1 );
	}
    if (buf[0] != 037 || (buf[1] != 0213 && buf[1] != 0236))
		/* not compressed, remove this module from the stream */
		return( 1 );

	if (!(gunzip_stack = malloc( GUNZIP_STACK_SIZE ))) {
		printf( "Out of memory for gunzip stack!\n" );
		return( -1 );
	}
	gunzip_sp = 0;

	if (!(inbuf = malloc( INBUFSIZ ))) {
		printf( "Out of memory for gunzip input buffer!\n" );
		return( -1 );
	}

#ifdef DEBUG_GUNZIP
	xfile = fopen( "xx", "wb" );
#endif
	return( 0 );
}

static __inline__ unsigned long getsp( void )
{
	ulg ret;
	__asm__ __volatile__
		( "movl	%%sp,%0" : "=r" (ret) : );
	return( ret );
}

static long gunzip_fillbuf( void *buf )
{
	previous_window = window;
	window = buf;
	return( call_gunzip() );
}

static int gunzip_close( void )
{
	free( gunzip_stack );
	free( inbuf );
	sclose();
#ifdef DEBUG_GUNZIP
	fclose( xfile );
#endif
	return( 0 );
}

static void gzip_mark( void **ptr )
{
}

static void gzip_release( void **ptr )
{
}

/* This function does most of the magic for implementing a second stack for
 * gunzip(). This is necessary because lib/inflate.c only provides a callback
 * (flush_window()) that can store data away. But we need to actually return
 * from out fillbuf method to implement the streaming. (Otherwise, the whole
 * file would have to be uncompressed and buffered as a whole.)
 *
 * The solution to this problem is a second stack on which gunzip() runs. If
 * flush_window() is called, it saves state and then switches back to the main
 * stack, from which we can return to our caller. For resuming at the point
 * where it left off, we simply restore the gunzip stack again. A second
 * return value in d1 distinguishes returns from inside flush_window() and
 * "normal" returns from gunzip() itself. The latter either indicate EOF or
 * error.
 */
static int call_gunzip( void )
{
	int rv = 0;
	
	/* avoid warnings about unused variables (appear only in asm) */
	(void)&main_sp;
	(void)&main_fp;
	(void)&gunzip_jumpback;
	(void)gunzip;
	
	if (!gunzip_sp) {
		register int asm_rv __asm__ ("d0");
		/* gunzip() wasn't called before: set up its stack and call the main
		 * function */
		__asm__ __volatile__ (
			"movl	%%sp,main_sp\n\t"	/* save current sp */
			"movl	%%a6,main_fp\n\t"	/* and fp */
			"movl	%1,%%sp\n\t"		/* move to new stack */
			"jbsr	gunzip\n\t"			/* call the function */
		"_return_from_flush:\n\t" 		/* point of coming back */
			"movl	main_sp,%%sp\n\t"	/* restore main sp */
			"movl	main_fp,%%a6" 		/* and fp */
			: "=d" (asm_rv)
			: "g" (gunzip_stack+GUNZIP_STACK_SIZE-sizeof(int))
			: "d1", "d2", "d3", "d4", "d5", "d6", "d7", "a0", "a1", "a2", "a3",
			  "a4", "a5", "memory" /* all regs possibly clobbered */
			);
		rv = asm_rv;
	}
	else {
		/* gunzip() is already active, jump to where it left off */
		__asm__ __volatile__ (
			"movl	%%sp,main_sp\n\t"	/* save current sp */
			"movl	%%a6,main_fp\n\t"	/* and fp */
			"movl	gunzip_jumpback,%%a0\n\t"
			"jmp	%%a0@"
			: /* no outputs */
			: /* no inputs */
			: "d0", "d1", "a0", "a1", "memory" /* clobbered regs */
			);
	}
	return( rv );		/* 0 for EOF, -1 for error, > 0 if from flush_window */
}

/* This is used in flush_window() to return into call_gunzip() */
#define RETURN_TO_MAIN_STACK()												\
	__asm__ __volatile__ (													\
		"movml	%%d2-%%d7/%%a2-%%a6,%%sp@-\n\t"	/* save call-saved regs */	\
		"movl	%%sp,gunzip_sp\n\t" 			/* save current sp */		\
		"movl	#1f,gunzip_jumpback\n\t" 		/* save return address */	\
		"movl	outcnt,%%d0\n\t"				/* return value */			\
		"jmp	_return_from_flush\n" 			/* and return... */			\
	"1:\tmovl	gunzip_sp,%%sp\n\t" 			/* restore sp */			\
		"movml	%%sp@+,%%d2-%%d7/%%a2-%%a6"		/* restore registers */		\
		: /* no outputs */													\
		: /* no inputs */													\
		: "d0", "d1", "a0", "a1", "memory" /* clobbered regs */				\
		)

/*
 * Fill the input buffer. This is called only when the buffer is empty
 * and at least one byte is really needed.
 */
static int fill_inbuf( void )
{
    if (exit_code)
		return( -1 );

    insize = sread( inbuf, INBUFSIZ );
    if (insize <= 0)
		return( -1 );

    inptr = 1;
    return( inbuf[0] );
}

/*
 * Write the output window window[0..outcnt-1] and update crc and bytes_out.
 * (Used for the decompressed data only.)
 */
static void flush_window( void )
{
    ulg c = crc;         /* temporary variable */
    unsigned n;
    uch *in, ch;
    
    in = window;
    for( n = 0; n < outcnt; n++ ) {
	    ch = *in++;
	    c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
    }
    crc = c;
	bytes_out += (ulg)outcnt;
#ifdef DEBUG_GUNZIP
	fwrite( window, outcnt, 1, xfile );
#endif

	/* return to call_gunzip(), next call to it resumes here */
	RETURN_TO_MAIN_STACK();
	
	outcnt = 0;
}

static void error( char *x )
{
    printf( "\n%s\n", x);
    exit_code = 1;
}

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