Diff: main.c

Revision:

0:b7eda4fdb627

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.c	Thu Oct 29 00:45:39 2015 +0000
@@ -0,0 +1,45 @@
+#include "mbed.h"
+
+__asm void my_strcpy(const char *src, char *dst);
+__asm void my_capitalize(char *str);
+
+int main(void){
+    const char a[] = "Hello World!";
+    char b[20];
+    
+    my_strcpy(a,b);
+    my_capitalize(b);
+    
+    while(1)
+    ;    
+}
+
+__asm void my_strcpy(const char *src, char *dst){
+loop
+    LDRB r2, [r0]   ; Load byte into r2 from memory, pointed to by r0 (src pointer)
+    ADDS r0, #1     ; Increment src pointer
+    STRB r2, [r1]   ; Store byte in r2 into memory pointed to by (dst pointer)
+    ADDS r1, #1     ; Increment dst pointer
+    CMP r2, #0      ; What the byte == 0?
+    BNE loop        ; If not, repeat the loop
+    BX lr           ; Else return from subroutine    
+}
+
+__asm void my_capitalize(char *str){
+cap_loop
+    LDRB r1, [r0]   ; Load byte into r1 from memory pointed to by r0 (str pointer)
+    CMP r1, #'a'-1  ; Compare byte with the character before 'a'
+    BLS cap_skip    ; If byte is lower or same, then skip this byte
+    
+    CMP r1, #'z'    ; Compare it with the 'z' character
+    BHI cap_skip    ; If it is higher, then skip this byte
+    
+    SUBS r1, #32    ; Else subtract out difference to capitalize it
+    STRB r1, [r0]   ; Store the capitalized byte back in memory
+
+cap_skip
+    ADDS r0, r0, #1 ; Increment str pointer
+    CMP r1, #0      ; Was the byte 0?
+    BNE cap_loop    ; IF not, repeat the loop
+    BX lr           ; Else return from subroutine
+}
\ No newline at end of file