/*
* Copyright (C) 1996-2002 Markus Franz Xaver Johannes Oberhumer
*
* This file is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* Originally this code was part of ucl the data compression library
* for upx the ``Ultimate Packer of eXecutables''.
*
* - Converted to gas assembly, and refitted to work with etherboot.
* Eric Biederman 20 Aug 2002
*
* - Structure modified to be a subroutine call rather than an
* executable prefix.
* Michael Brown 30 Mar 2004
*
* - Modified to be compilable as either 16-bit or 32-bit code.
* Michael Brown 9 Mar 2005
*/
FILE_LICENCE ( GPL2_OR_LATER )
/****************************************************************************
* This file provides the decompress() and decompress16() functions
* which can be called in order to decompress an image compressed with
* the nrv2b utility in src/util.
*
* These functions are designed to be called by the prefix. They are
* position-independent code.
*
* The same basic assembly code is used to compile both
* decompress() and decompress16().
****************************************************************************
*/
.text
.arch i386
.section ".prefix.lib", "ax", @progbits
#ifdef CODE16
/****************************************************************************
* decompress16 (real-mode near call, position independent)
*
* Decompress data in 16-bit mode
*
* Parameters (passed via registers):
* %ds:%esi - Start of compressed input data
* %es:%edi - Start of output buffer
* Returns:
* %ds:%esi - End of compressed input data
* %es:%edi - End of decompressed output data
* All other registers are preserved
*
* NOTE: It would be possible to build a smaller version of the
* decompression code for -DKEEP_IT_REAL by using
* #define REG(x) x
* to use 16-bit registers where possible. This would impose limits
* that the compressed data size must be in the range [1,65533-%si]
* and the uncompressed data size must be in the range [1,65536-%di]
* (where %si and %di are the input values for those registers). Note
* particularly that the lower limit is 1, not 0, and that the upper
* limit on the input (compressed) data really is 65533, since the
* algorithm may read up to three bytes beyond the end of the input
* data, since it reads dwords.
****************************************************************************
*/
#define REG(x) e ## x
#define ADDR32 addr32
.code16
.globl decompress16
decompress16:
#else /* CODE16 */
/****************************************************************************
* decompress (32-bit protected-mode near call, position independent)
*
* Parameters (passed via registers):
* %ds:%esi - Start of compressed input data
* %es:%edi - Start of output buffer
* Returns:
* %ds:%esi - End of compressed input data
* %es:%edi - End of decompressed output data
* All other registers are preserved
****************************************************************************
*/
#define REG(x) e ## x
#define ADDR32
.code32
.globl decompress
decompress:
#endif /* CODE16 */
#define xAX REG(ax)
#define xCX REG(cx)
#define xBP REG(bp)
#define xSI REG(si)
#define xDI REG(di)
/* Save registers */
push %xAX
pushl %ebx
push %xCX
push %xBP
/* Do the decompression */
cld
xor %xBP, %xBP
dec %xBP /* last_m_off = -1 */
jmp dcl1_n2b
decompr_literals_n2b:
ADDR32 movsb
decompr_loop_n2b:
addl %ebx, %ebx
jnz dcl2_n2b
dcl1_n2b:
call getbit32
dcl2_n2b:
jc decompr_literals_n2b
xor %xAX, %xAX
inc %xAX /* m_off = 1 */
loop1_n2b:
call getbit1
adc %xAX, %xAX /* m_off = m_off*2 + getbit() */
call getbit1
jnc loop1_n2b /* while(!getbit()) */
sub $3, %xAX
jb decompr_ebpeax_n2b /* if (m_off == 2) goto decompr_ebpeax_n2b ? */
shl $8, %xAX
ADDR32 movb (%xSI), %al /* m_off = (m_off - 3)*256 + src[ilen++] */
inc %xSI
xor $-1, %xAX
jz decompr_end_n2b /* if (m_off == 0xffffffff) goto decomp_end_n2b */
mov %xAX, %xBP /* last_m_off = m_off ?*/
decompr_ebpeax_n2b:
xor %xCX, %xCX
call getbit1
adc %xCX, %xCX /* m_len = getbit() */
call getbit1
adc %xCX, %xCX /* m_len = m_len*2 + getbit()) */
jnz decompr_got_mlen_n2b /* if (m_len == 0) goto decompr_got_mlen_n2b */
inc %xCX /* m_len++ */
loop2_n2b:
call getbit1
adc %xCX, %xCX /* m_len = m_len*2 + getbit() */
call getbit1
jnc loop2_n2b /* while(!getbit()) */
inc %xCX
inc %xCX /* m_len += 2 */
decompr_got_mlen_n2b:
cmp $-0xd00, %xBP
adc $1, %xCX /* m_len = m_len + 1 + (last_m_off > 0xd00) */
push %xSI
ADDR32 lea (%xBP,%xDI), %xSI /* m_pos = dst + olen + -m_off */
rep
es ADDR32 movsb /* dst[olen++] = *m_pos++ while(m_len > 0) */
pop %xSI
jmp decompr_loop_n2b
getbit1:
addl %ebx, %ebx
jnz 1f
getbit32:
ADDR32 movl (%xSI), %ebx
sub $-4, %xSI /* sets carry flag */
adcl %ebx, %ebx
1:
ret
decompr_end_n2b:
/* Restore registers and return */
pop %xBP
pop %xCX
popl %ebx
pop %xAX
ret
