kolibrios-fun/drivers/ddk/string/strchr.S

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# strchr() Author: Kees J. Bot 1 Jan 1994
# char *strchr(const char *s, int c)
# Look for a character in a string.
.intel_syntax
.globl _strchr
.text
.align 16
_strchr:
push ebp
mov ebp, esp
push edi
cld
mov edi, [ebp+8] # edi = string
mov edx, 16 # Look at small chunks of the string
next:
shl edx, 1 # Chunks become bigger each time
mov ecx, edx
xorb al, al # Look for the zero at the end
repne scasb
pushf # Remember the flags
sub ecx, edx
neg ecx # Some or all of the chunk
sub edi, ecx # Step back
movb al, [ebp+12] # The character to look for
repne scasb
je found
popf # Did we find the end of string earlier?
jne next # No, try again
xor eax, eax # Return NULL
pop edi
pop ebp
ret
found:
pop eax # Get rid of those flags
lea eax, [edi-1] # Address of byte found
pop edi
pop ebp
ret