请教下面函数的ecx是什么

.text:00401000 ;
.text:00401000 ; 赏屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯?
.text:00401000 ; ?    This file is generated by The Interactive Disassembler (IDA)        ?
.text:00401000 ; ?    Copyright (c) 2005 by DataRescue sa/nv, <ida@datarescue.com>        ?
.text:00401000 ; ?            Licensed to: Lennart Reus, 1 user, std, 07/2003             ?s
.text:00401000 ; 韧屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯?
.text:00401000 ;
.text:00401000 ; File Name   : K:\ArmAsm\armasm.exe
.text:00401000 ; Format      : Portable executable for 80386 (PE)
.text:00401000 ; Imagebase   : 400000
.text:00401000 ; Section 1. (virtual address 00001000)
.text:00401000 ; Virtual size                  : 0003286E ( 206958.)
.text:00401000 ; Section size in file          : 00033000 ( 208896.)
.text:00401000 ; Offset to raw data for section: 00001000
.text:00401000 ; Flags 60000020: Text Executable Readable
.text:00401000 ; Alignment     : default
.text:00401000
.text:00401000
.text:00401000 unicode         macro page,string,zero
.text:00401000                 irpc c,<string>
.text:00401000                 db '&c', page
.text:00401000                 endm
.text:00401000                 ifnb <zero>
.text:00401000                 dw zero
.text:00401000                 endif
.text:00401000 endm
.text:00401000
.text:00401000                 .686p
.text:00401000                 .mmx
.text:00401000                 .model flat
.text:00401000
.text:00401000 ; 屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯?
.text:00401000
.text:00401000 ; Segment type: Pure code
.text:00401000 ; Segment permissions: Read/Execute
.text:00401000 _text           segment para public 'CODE' use32
.text:00401000                 assume cs:_text
.text:00401000                 ;org 401000h
.text:00401000                 assume es:nothing, ss:nothing, ds:_data, fs:nothing, gs:nothing
.text:00401000
.text:00401000 ; 圹圹圹圹圹圹圹?S U B R O U T I N E 圹圹圹圹圹圹圹圹圹圹圹圹圹圹圹圹圹圹圹?
.text:00401000
.text:00401000
.text:00401000 sub_401000      proc near               ; CODE XREF: sub_404780+1FCAp
.text:00401000                                         ; sub_404780+202Cp ...
.text:00401000
.text:00401000 arg_0           = dword ptr  4
.text:00401000
.text:00401000                 mov     eax, [esp+arg_0]
.text:00401004                 shl     eax, 4
.text:00401007                 xor     eax, [ecx];;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
.text:00401009                 and     eax, 0F0h
.text:0040100E                 xor     [ecx], eax
.text:00401010                 call    sub_41DA50
.text:00401015                 retn    4
.text:00401015 sub_401000      endp