assembly - 装配迷宫求解器不修改 si di 和 bx 寄存器
问题描述
我正在尝试在汇编中编写迷宫求解器。我们得到一个驱动程序，它发送 si 寄存器中的当前 x 位置、di 寄存器中的 y 位置、bx 寄存器中的移动方向以及 bp 寄存器中的迷宫本身。
我应该检查鼠标是否可以向左移动，然后向前，然后向右然后向后移动。
我的问题是，当我尝试运行它时，它似乎没有修改 si di 或 bx 寄存器，我无法找出原因。
有人可以看看是否有任何明显的问题可能导致这种情况。我从来没有在这里发帖，但我已经没有选择了，非常感谢。
;---------------------------------------------------------------------
; Program: nextval subroutine
;
; Function: Find next mouse move in an array 15 by 30.
; We can move into a position if its contents is blank ( 20h ).
;
; Input: Calling sequence is:
; x pointer si
; y pointer di
; dir pointer bx E=1 S=2 W=3 N=4
; maze pointer bp
;
; Output: x,y,dir modified in caller's data segment
;
; Owner: Dana A. Lasher
;
; Date: Update Reason
; --------------------------
; 11/06/2016 Original version
;
;
;---------------------------------------
.model small ;64k code and 64k data
.8086 ;only allow 8086 instructions
public nextval ;allow extrnal programs to call
;---------------------------------------
;---------------------------------------
.data ;start the data segment
;---------------------------------------
value db 30
;---------------------------------------
.code ;start the code segment
;---------------------------------------
; Save any modified registers
;---------------------------------------
nextval:
push cx ; save cx register
mov cl, 0 ; set testing phase to 0 stored in ch
;---------------------------------------
; Code to make 1 move in the maze
;---------------------------------------
testnext:
push ax ; save ax register
push dx ; save dx register
push bx ; save bx register
push si ; save si register
push di ; sav di register
mov dh, [si] ; load the x value into dh
mov dl, [di] ; load the y value into dl
inc cl ; increment the testing phase
direction:
cmp word ptr [bx], 1 ; is the moving direction East
je goingeast ; yes, jump to the going east function
cmp word ptr [bx], 2 ; is the moving direction south
je goingsouth ; yes, jump to the going south function
cmp word ptr [bx], 3 ; is the moving direction west
je goingwest ; yes, jump to the going west function
cmp word ptr [bx], 4 ; is the moving direction north
je goingnorth ; yes, jump to the going north function
jmp exit
;---------------------------------------
; Going East Check order: N-E-S-W
;---------------------------------------
goingeast:
cmp cl, 1 ; is the testing phase phase 1
je checknorth ; yes, check to see if a move north is valid
cmp cl, 2 ; is the testing phase phase 2
je checkeast ; yes, check to see if a move east is valid
cmp cl, 3 ; is the testing phase phase 3
je checksouth ; yes, check to see if a move south is valid
cmp cl, 4 ; is the testing phase phase 4
je checkwest ; yes, check to see if a move west is valid
jmp exit
;---------------------------------------
; Going South Check order: E-S-W-N
;---------------------------------------
goingsouth:
cmp cl, 1 ; is the testing phase phase 1
je checkeast ; yes, check to see if a move east is valid
cmp cl, 2 ; is the testing phase phase 2
je checksouth ; yes, check to see if a move south is valid
cmp cl, 3 ; is the testing phase phase 3
je checkwest ; yes, check to see if a move west is valid
cmp cl, 4 ; is the testing phase phase 4
je checknorth ; yes, check to see if a move north is valid
jmp exit
;---------------------------------------
; Going West Check order: S-W-N-E
;---------------------------------------
goingwest:
cmp cl, 1 ; is the testing phase phase 1
je checksouth ; yes, check to see if a move south is valid
cmp cl, 2 ; is the testing phase phase 2
je checkwest ; yes, check to see if a move west is valid
cmp cl, 3 ; is the testing phase phase 3
je checknorth ; yes, check to see if a move north is valid
cmp cl, 4 ; is the testing phase phase 4
je checkeast ; yes, check to see if a move east is valid
jmp exit
;---------------------------------------
; Going North Check order: W-N-E-S
;---------------------------------------
goingnorth:
cmp cl, 1 ; is the testing phase phase 1
je checkwest ; yes, check to see if a move west is valid
cmp cl, 2 ; is the testing phase phase 2
je checknorth ; yes, check to see if a move north is valid
cmp cl, 3 ; is the testing phase phase 3
je checkeast ; yes, check to see if a move east is valid
cmp cl, 4 ; is the testing phase phase 4
je checksouth ; yes, check to see if a move south is valid
jmp exit
;---------------------------------------
; Check East X + 1 Y same
;---------------------------------------
checkeast:
inc byte ptr [si] ; increment the x position
inc dh ; incremement dh to the x position being tested
mov ch, 1 ; update the testing direction ch to 1
jmp testposition ; jump to the test position function
;---------------------------------------
; Check South X same Y + 1
;---------------------------------------
checksouth:
inc byte ptr [di] ; increment the y position
inc dl ; increment dl to the y position being tested
mov ch, 2 ; update the testing direction ch to 2
jmp testposition ; jump to the test position function
;---------------------------------------
; Check West X - 1 Y same
;---------------------------------------
checkwest:
dec byte ptr [si] ; decrement the x position
dec dh ; update dh to the x position being tested
mov ch, 3 ; update the testing direction ch to 3
jmp testposition ; jump to the test position function
;---------------------------------------
; Check North X same Y - 1
;---------------------------------------
checknorth:
dec byte ptr [di] ; increment the y position
dec dl ; update dl to the y position being tested
mov ch, 4 ; update the testing direction ch to 4
testposition:
mov ax, [di] ; move the y position being tested into the ax register
dec ax ; decrement the ax register for the offset calculation
mul [value] ; multiply the al register by 30 and store the product in ax
add ax, [si] ; add the x position to the ax
dec ax ; decrement the ax register for the offset calculation
mov [si], ax ; move the offset calculated inside of ax into si
mov ax, ds:[bp + si] ; access the maze using data segment override with the offset in si
cmp ax, 20h ; position in the maze at the offset empty
je exit ; yes jump to the exit function
pop di ; no, restore the di register
pop si ; no, restore the si register
pop bx ; no, restore the bx register
pop dx ; no, restore the dx register
pop ax ; no, restore the ax register
jmp testnext ; test the next move direction
;---------------------------------------
; Restore registers and return
;---------------------------------------
exit:
pop di ; restore the di register
pop si ; restore the si register
pop bx ; restore the bx register
; here the dx and cx registers should still have the needed information
mov byte ptr [si], dh ; update x position
mov byte ptr [di], dl ; update y position
mov byte ptr [bx], ch ; update moving direction
pop dx ; restore the dx register
pop ax ; restore the ax register
pop cx ; restore the cx register
ret ; return
;---------------------------------------
end nextval
解决方案
; 输出：调用者数据段中修改的 x,y,dir
鉴于序言中的这句话，我认为迷宫求解器不修改SI、DI和BX寄存器是一件好事......
过早销毁输入数据
代码中的问题之一是您在测试进行时破坏了原始数据。而且因为你需要多次测试，后续的测试将使用垃圾数据。
在该过程中，您只能使用您在和寄存器中加载的X和Y的本地副本。DHDL
这些必须去：
inc byte ptr [si] ; increment the x position inc byte ptr [di] ; increment the y position dec byte ptr [si] ; decrement the x position dec byte ptr [di] ; increment the y position
虚假地址计算
mov [si], ax ; move the offset calculated inside of ax into si
该指令与评论所说的不同。那将是
mov si, ax。
同样重要的是，您不应该SI在程序的这一点上进行破坏！从testposition
dec ax部分的说明中，我们看到您希望X和Y是基于 1 的坐标。这很好，但您必须在计算中使用本地修改的值：DHDL偏移地址计算适合字节大小的数组（迷宫）。因此，您不应该从中比较一个词！
尝试下一个代码：
mov al, DL ; move the y position being tested into the AL register
dec al ; decrement the AL register for the offset calculation
mul [value] ; multiply the al register by 30 and store the product in ax
add al, DH ; add the x position to the ax
adc ah, 0
dec ax ; decrement the ax register for the offset calculation
push si ; Preserve SI
mov si, ax ; move the offset calculated inside of ax into si
mov al, ds:[bp + si] ; access the maze using data segment override with offset si
pop si ; Restore SI
cmp al, 20h ; position in the maze at the offset empty
je exit ; yes jump to the exit function
最后一个问题
您确定方向变量dir实际上是一个word。我会更早地期望在一个字节大小的变量中找到那个小值。
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