Il s’agit d’une version asm du crc32 présenté dans la rfc gzip (1952).
format ELF64 executable 3
entry start
include 'include/linux/lin64a.inc'
interpreter '/lib64/ld-linux-x86-64.so.2'
needed 'libc.so.6'
import printf
;-------------------------------------------------------------------------
segment readable executable
;-------------------------------------------------------------------------
start:
mov esi,buffer_len
mov edi,buffer
call update_crc
mov esi,eax
mov edi,formh
xor eax,eax
call [printf]
exit:
xor edi,edi
mov eax,_exit
syscall
update_crc:
cmp dword [crc_table_computed],0
jnz @f
mov ebp,esi
call make_crc_table
mov ecx,ebp
@@:
xor eax,eax
not eax
xor edx,edx
@@:
mov dl,al
mov bl,byte [edi]
xor dl,bl
inc edi
mov ebx,dword [esi+edx*4]
shr eax,8
xor eax,ebx
dec ecx
jnz @b
xor eax,0xffffffff
ret
make_crc_table:
mov esi,crc_table
xor ecx,ecx
A1:
mov eax,ecx
mov bl,8
A2:
mov dl,al
and dl,1
cmp dl,1
jnz @f
mov edx,eax
shr edx,1
mov eax,0xedb88320
xor eax,edx
jmp A3
@@:
shr eax,1
A3:
dec bl
jnz A2
mov dword [esi+ecx*4],eax
inc cl
jnz A1
mov dword [crc_table_computed],1
ret
;-------------------------------------------------------------------------
segment readable writeable
;-------------------------------------------------------------------------
crc_table rd 256
crc_table_computed dd 0
buffer db 'Life, the Universe and everything'
buffer_len = $-bufferLe même crc32 mais en version x32 stack, sans buffer.
format ELF executable 3
entry start
include 'include/linux/lin32a.inc'
interpreter '/lib/ld-linux.so.2'
needed 'libc.so.6'
import printf
;-------------------------------------------------------------------------
segment readable executable
;-------------------------------------------------------------------------
start:
mov esi,buffer_len
mov edi,buffer
call update_crc
invoke printf,formh,eax
xor ebx,ebx
mov eax,_exit
int 0x80
update_crc:
cmp dword [crc_table_computed],0
jnz @f
mov ebp,esi
call make_crc_table
mov ecx,ebp
@@:
sub esp,8
xor eax,eax
not eax
xor edx,edx
@@:
mov dl,al
mov bl,byte [edi]
xor dl,bl
inc edi
neg edx
mov ebx,dword [esp+edx*4]
neg edx
shr eax,8
xor eax,ebx
dec ecx
jnz @b
xor eax,0xffffffff
add esp,8
ret
make_crc_table:
xor ecx,ecx
sub esp,4
A1:
mov eax,ecx
mov bl,8
A2:
mov dl,al
and dl,1
cmp dl,1
jnz @f
mov edx,eax
shr edx,1
mov eax,0xedb88320
xor eax,edx
jmp A3
@@:
shr eax,1
A3:
dec bl
jnz A2
neg ecx
mov dword [esp+ecx*4],eax
neg ecx
inc cl
jnz A1
mov dword [crc_table_computed],1
add esp,4
ret
;-------------------------------------------------------------------------
segment readable writeable
;-------------------------------------------------------------------------
crc_table_computed dd 0
buffer db 'Life, the Universe and everything'
buffer_len = $-bufferA compiler avec Fasm