Libc-825.40.1.tar.gz

[apple/libc.git] / arm / string / strchr.s

diff --git a/arm/string/strchr.s b/arm/string/strchr.s
index 58981cb07aff11d2f3dedee7bbd50214c8ff37c6..229db7bad0884cdc68a4d562148e64509964b35f 100644 (file)
--- a/arm/string/strchr.s
+++ b/arm/string/strchr.s
@@ -20,4 +20,42 @@
  * 
  * @APPLE_LICENSE_HEADER_END@
  */
+ 
+//  char * strchr(const char *s, int c);
+//
+//  The strchr( ) function locates the first occurence of c (converted to a
+//  char) in the string s.  If c is '\0', the function locates the terminating
+//  '\0' byte.
 
+.text
+.syntax unified
+.code 32
+.globl _strchr
+
+.align 3
+_strchr:
+//  Setup a frame and convert c to a char.
+    push   {r7,lr}
+    mov     r7,         sp
+    and     r1,     r1, #0xff
+
+//  Basic character-by-character search for c; on each pass through the loop
+//  we load a byte from s and increment s.  We then check if this byte is equal
+//  to either c or to '\0'; if not, we continue the loop.
+0:  ldrb    r2,    [r0],#1
+    cmp     r2,     r1
+    tstne   r2,     r2
+    bne     0b
+
+//  Either we have found a match, or we have reached the end of the string (or
+//  both, if c == '\0').  Because we incremented s after loading the last
+//  character, we need to decrement the pointer by one to get a pointer to
+//  either the matching or terminating character. 
+    sub     r0,     r0, #1
+    
+//  Now compare the last character we loaded to the character that we're
+//  searching for.  If they don't match, the character was not found in the
+//  string, so return NULL.
+    cmp     r2,     r1
+    movne   r0,     #0
+    pop    {r7,pc}