File: strlen.S

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avr-libc 20020203-2
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#include "macros.inc"

#define src_hi r25
#define src_lo r24

; size_t strlen(const char *src)
; 10 words, (14 + strlen(src) * 5) cycles

	.text
	.global	_U(strlen)
	.type	_U(strlen), @function
_U(strlen):
	LOAD_Z(src_lo, src_hi)
.strlen_loop:
	ld	__tmp_reg__, Z+
	tst	__tmp_reg__
	brne	.strlen_loop
; Z points one character past the terminating NUL
; return Z - 1 - src = (-1 - src) + Z = ~src + Z
	com	src_lo
	com	src_hi
	add	src_lo, ZL
	adc	src_hi, ZH
	ret
.strlen_end:
	.size	_U(strlen), .strlen_end - _U(strlen)