ARM 程序集 - 将输入文件更改为仅包含大写字母和空格，写入输出

Question

我现在正在学习 x86 课程，我们有一个 ARM 程序集作业，它是我们所做的 x86 作业的副本。基本上它从文件中读取，将小写字母更改为大写，并保留空格。所以它只写大写字母（如果是小写则更改小写字母），并复制空格，同时去掉数字和字符。我们只使用十六进制字符 00h-7F（即使我们拥有的最低可用字符是 0x20）。我试图将我的代码从 x86 转换为 ARM，但它只是直接通过，没有写入输出。任何想法为什么，以及如何解决它？

我写了标有“检查是否小写”“检查是否大写”和“检查是否空格”的部分

;---------------------------------------------------------------------
; File:     ARMkey.s
;
; Function: This program copies an ASCII file
;           It assumes the file uses CR/LF as the end of line sequence
;           - It opens an input file named key.in
;           - It opens an output file named key.out
;           - It reads one line of text from the input file.
;           - It writes that one line to the output file, only using chars 00h-7Fh then a CR LF
;           - It loops until it reaches end of file
;           - It closes the input and output file
;
;
;---------------------------------------------------------------------


;----------------------------------
; Software Interrupt values
;----------------------------------
         .equ SWI_Open,  0x66     ;Open  a file
         .equ SWI_Close, 0x68     ;Close a file
         .equ SWI_PrStr, 0x69     ;Write a null-ending string
         .equ SWI_RdStr, 0x6a     ;Read a string and terminate with null char
         .equ SWI_Exit,  0x11     ;Stop execution
;----------------------------------

         .global   _start
         .text

_start:
;----------------------------------
; open input file
; - r0 points to the file name
; - r1 0 for input
; - the open swi is 66h
; - after the open r0 will have the file handle
;----------------------------------
         ldr  r0, =InFileName     ;r0 points to the file name
         ldr  r1, =0              ;r1 = 0 specifies the file is input
         swi  SWI_Open            ;open the file ... r0 will be the file handle
         ldr  r1, =InFileHandle   ;r1 points to handle location
         str  r0, [r1]            ;store the file handle
;----------------------------------


;----------------------------------
; open output file
; - r0 points to the file name
; - r1 1 for output
; - the open swi is 66h
; - after the open r0 will have the file handle
;----------------------------------
         ldr  r0, =OutFileName    ;r0 points to the file name
         ldr  r1, =1              ;r1 = 1 specifies the file is output
         swi  SWI_Open            ;open the file ... r0 will be the file handle
         ldr  r1, =OutFileHandle  ;r1 points to handle location
         str  r0, [r1]            ;store the file handle
;----------------------------------


;----------------------------------
; read a string from the input file
; - r0 contains the file handle
; - r1 points to the input string buffer
; - r2 contains the max number of characters to read
; - the read swi is 6ah
; - the input string will be terminated with 0
;----------------------------------
_read:                            ;
         ldr  r0, =InFileHandle   ;r0 points to the input file handle
         ldr  r0, [r0]            ;r0 has the input file handle
         ldr  r1, =String         ;r1 points to the input string
         ldr  r2, =128            ;r2 has the max size of the input string
         swi  SWI_RdStr           ;read a string from the input file
         cmp  r0,#0               ;no characters read means EOF
         beq  _exit               ;so close and exit
;----------------------------------

;----------------------------------
; Check if Lower Case Letter
;----------------------------------

     cmp    r1, #0x61              ;check against lowercase a
     blt    _notlower              ;if less go to notlow
     cmp    r1, #0x7A              ;check against lowercase z
     bgt    _notlower
     sub    r1, r1, #0x14          ;Make letter uppercase
     bal    _read

;----------------------------------
; Check if Upper Case Letter
;----------------------------------

_notlower:
     cmp    r1, #0x41             ;dl < A
     blt    _space                ;jump to not letter
     cmp    r1, #0x5A             ;dl > Z
     blt    _space                ;jump to not letter

;----------------------------------
; Check if Space
;----------------------------------

_space:
     cmp    r1, #0x20             ; r1 = space?
     beq    _read                 ; yes, get new letter


;----------------------------------
; Write the outputs string
;----------------------------------
_write:                           ;
         ldr  r0, =OutFileHandle  ;r0 points to the output file handle
         ldr  r0, [r0]            ;r0 has the output file handle
         ldr  r1, =String         ;r1 points to the output string
         swi  SWI_PrStr           ;write the null terminated string
                                  ;
         ldrb r1, [r1]            ;get the first byte of the line



         cmp  r1, #0x1A           ;if line was DOS eof then do not write CRLF
         beq  _read               ;so do next read
                                  ;
         ldr  r1, =CRLF           ;r1 points to the CRLF string
         swi  SWI_PrStr           ;write the null terminated string
                                  ;
         bal  _read               ;read the next line
;----------------------------------


;----------------------------------
; Close input and output files
; Terminate the program
;----------------------------------
_exit:                            ;
         ldr  r0, =InFileHandle   ;r0 points to the input  file handle
         ldr  r0, [r0]            ;r0 has the input file handle
         swi  SWI_Close           ;close the file
                                  ;
         ldr  r0, =OutFileHandle  ;r0 points to the output file handle
         ldr  r0, [r0]            ;r0 has the output file handle
         swi  SWI_Close           ;close the file
                                  ;
         swi  SWI_Exit            ;terminate the program
;----------------------------------


         .data
;----------------------------------
InFileHandle:  .skip 4            ;4 byte field to hold the input  file handle
OutFileHandle: .skip 4            ;4 byte field to hold the output file handle
                                  ;
InFileName:    .asciz "KEY.IN"   ;Input  file name, null terminated
                                  ;
String:        .skip 128          ;reserve a 128 byte string
                                  ;
CRLF:          .byte 13, 10, 0    ;CR LF
                                  ;
OutFileName:   .asciz "KEY.OUT"  ;Output file name, null terminated
;----------------------------------


         .end

测试文件包含以下字符：

 !"#$%&'()*+,-/0123456789:;<=>?@
 ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`
 abcdefghijklmnopqrstuvwxyz{|}~

它应该只输出：

 ABCDEFGHIJKLMNOPQRSTUVWXYZ 
 ABCDEFGHIJKLMNOPQRSTUVWXYZ

Answer 1

您的代码有多个问题，您可能应该先制作伪代码或流程图来弄清楚算法。

类似：

while(ReadString(String, 128) != 0)
{
    for(r0 = r1 = String; *r0 != 0; r0++)
    {
        if (IsLower(*r0))
        {
            *r1++ = UpperCase(*r0);
        } else if (IsUpper(*r0) || IsSpace(*r0)) {
            *r1++ = *r0;
        }
    }
    *r0 = 0; /* terminate */
    WriteString(String);
}

现在，将其转换为汇编代码是一件简单的事情。比如：

_read:
     ldr  r0, =InFileHandle   ;r0 points to the input file handle
     ldr  r0, [r0]            ;r0 has the input file handle
     ldr  r1, =String         ;r1 points to the input string
     ldr  r2, =128            ;r2 has the max size of the input string
     swi  SWI_RdStr           ;read a string from the input file
     cmp  r0,#0               ;no characters read means EOF
     beq  _exit               ;so close and exit

     ldr  r0, =String
     mov  r1, r0
charloop:
     ldrb r2, [r0]
     cmp  r2, #0
     beq  endofstring
     cmp  r2, #'z'
     bgt  skip
     cmp  r2, #'a'
     bge  lower
     cmp  r2, #'Z'
     bgt  skip
     cmp  r2, #'A'
     bge  copy
     cmp  r2, #' '
     beq  copy
     bal  skip
 lower:
     sub  r2, r2, #0x20
 copy:
     strb r2, [r1], #1
 skip:
     add  r0, r0, #1
     bal  charloop
 endofstring:
     strb r2, [r1]            ; copy the terminating zero

     ldr  r0, =OutFileHandle  ;r0 points to the output file handle
     ldr  r0, [r0]            ;r0 has the output file handle
     ldr  r1, =String         ;r1 points to the output string
     swi  SWI_PrStr           ;write the null terminated string
                              ;
     ldr  r1, =CRLF           ;r1 points to the CRLF string
     swi  SWI_PrStr           ;write the null terminated string
                              ;
     bal  _read               ;read the next line         

注意上面代码中的错误，我还没有测试过:)

PS：从上到下的差异是 0x20 而不是 20，而在您的代码中是 0x14。