Arm Assembly Rasperry-Pi: Converting a string to Upper case

问题

I´m working on a program in which the user enters his name, and the program should convert all lower case letters to upper case:

I am using the %s format to read the string:

.text
 ldr r0,=msj
 bl printf
 ldr r0,=format
 ldr r1,string
 bl scanf



.data
.align 2
msj: .asciz "Enter you name:  "
format: .asciz "%s"
string: .asciz ""

I have tried substracting 32 to each character but I think the strings are not in ascii numbers format.

Is there any way I can convert the entire word to Upper Case?

回答1:

This might work. I don't have any of my ARM material with me at the moment.

; call with address of string in 'R0'.
upperString:
1: ldrb r1,[r0],#1
   tst  r1      ; finished string with null terminator?
   bxeq lr      ; then done and return
   cmp  r1,#'a' ; less than a?
   blo  1b      ; then load next char.
   cmp  r1,#'z' ; greater than z?
   bhi  1b      ; then load next char.

   ; Value to upper case.
   sub  r1,r1,#('a' - 'A') ; subtract 32.
   strb r1,[r0,#-1] ; put it back to memory.
   b    1b      ; next character.

At least it is a good starting point. This is like wallyk's code, except I have assumed a null-terminated string instead of a pascal type string. To call it,

   ldr r0,=string
   bl  upperString

回答2:

This is the essential algorithm:

for (int idx = 0;  idx < len;  ++idx)
    if (str [idx] >= 'A'  &&  str [idx] <= 'Z')
         str [idx] += 'a' - 'A';

It has several parts you don't have. Scanning the string character by character. Inspecting for an uppercase letter. Adding (not subtracting) the lowercase/uppercase offset.

Note that this won't work for Unicode in general.

来源：https://stackoverflow.com/questions/16599258/arm-assembly-rasperry-pi-converting-a-string-to-upper-case

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assembly

arm

raspberry-pi