fox32rom: Add compare_string

fox32rom.def

@@ -61,6 +61,7 @@ copy_memory_words:                        jmp [0xF0046004]
 copy_string:                              jmp [0xF0046008]
 compare_memory_bytes:                     jmp [0xF004600C]
 compare_memory_words:                     jmp [0xF0046010]
+compare_string:                           jmp [0xF0046014]
 
 ; event types
 const EVENT_TYPE_MOUSE_CLICK:    0x00000000

main.asm

@@ -231,6 +231,7 @@ get_rom_version:
     data.32 copy_string
     data.32 compare_memory_bytes
     data.32 compare_memory_words
+    data.32 compare_string
 
     org.pad 0xF004F000
 standard_font_width:

string.asm

@@ -1,3 +1,5 @@
+; string copy/compare routines
+
 ; copy string from source pointer to destination pointer
 ; if the source and destination overlap, the behavior is undefined
 ; inputs:
@@ -22,3 +24,38 @@ copy_string_loop:
     pop r1
     pop r0
     ret
+
+; compare string from source pointer with destination pointer
+; inputs:
+; r0: pointer to source
+; r1: pointer to destinaton
+; outputs:
+; Z flag
+compare_string:
+    push r0
+    push r1
+compare_string_loop:
+    ; check if the strings match
+    cmp.8 [r0], [r1]
+    ifnz jmp compare_string_not_equal
+
+    ; if this is the end of string 1, then this must also be the end of string 2
+    ; the cmp above alredy ensured that both strings have a null-terminator here
+    cmp.8 [r0], 0
+    ifz jmp compare_string_equal
+
+    inc r0
+    inc r1
+    jmp compare_string_loop
+compare_string_not_equal:
+    ; Z flag is already cleared at this point
+    pop r1
+    pop r0
+    ret
+compare_string_equal:
+    ; set Z flag
+    mov r0, 0
+    cmp r0, 0
+    pop r1
+    pop r0
+    ret