Advanced

Remove Spaces

Remove all spaces from a string in place.

A null-terminated string is stored at x5000. Write a program to remove all spaces from the string, modifying it in place. Store the new length (after removing spaces) at x6000.

Example: "H E L L O" becomes "HELLO" and store 5 at x6000.

Requirements:
• Remove all space characters (ASCII x20 / decimal 32) from the string

• Modify the string in place at x5000

• Write a null terminator after the last non-space character

• Store the new length at x6000

Algorithm: Two-pointer approach
• Read pointer: scans through original string

• Write pointer: tracks where to write next non-space character

• For each character:

- If it's a space, skip it (advance read pointer only)
- If it's not a space, write it at the write pointer position, advance both
• At the end, write null terminator at write pointer position

• Length = write pointer - start address

.ORIG x3000
    LD R1, STRING_ADDR     ; R1 = read pointer
    LD R2, STRING_ADDR     ; R2 = write pointer
    AND R5, R5, #0         ; R5 = new length counter
 
    ; Read each character
READ_LOOP
    LDR R0, R1, #0         ; load char at read pointer
    BRz READ_DONE          ; if null, done reading
 
    ; Check if space (ASCII 32)
    ; If space, skip. If not space, write and count.
 
    ; ... your code here ...
 
    ADD R1, R1, #1         ; advance read pointer
    BRnzp READ_LOOP
 
READ_DONE
    ; Write null terminator at write pointer
    AND R0, R0, #0
    STR R0, R2, #0
 
    STI R5, RESULT
    HALT
 
STRING_ADDR .FILL x5000
RESULT .FILL x6000
NEG_SPACE .FILL #-32
.END

.ORIG x3000
    LD R1, STRING_ADDR     ; R1 = read pointer
    LD R2, STRING_ADDR     ; R2 = write pointer
    AND R5, R5, #0         ; R5 = new length counter

    ; Read each character
READ_LOOP
    LDR R0, R1, #0         ; load char at read pointer
    BRz READ_DONE          ; if null, done reading

    ; Check if space (ASCII 32)
    ; If space, skip. If not space, write and count.

    ; ... your code here ...

    ADD R1, R1, #1         ; advance read pointer
    BRnzp READ_LOOP

READ_DONE
    ; Write null terminator at write pointer
    AND R0, R0, #0
    STR R0, R2, #0

    STI R5, RESULT
    HALT

STRING_ADDR .FILL x5000
RESULT .FILL x6000
NEG_SPACE .FILL #-32
.END