arm64/lib/strlen.S

1 /* SPDX-License-Identifier: GPL-2.0-only */
3  * Copyright (c) 2013-2021, Arm Limited.
6  * https://github.com/ARM-software/optimized-routines/blob/98e4d6a5c13c8e54/string/aarch64/strlen.S
11 #include <asm/mte-def.h>
15  * ARMv8-a, AArch64, unaligned accesses, min page size 4k.
22 #define len		x0  macro
36 	/* NUL detection works on the principle that (X - 1) & (~X) & 0x80
37 	   (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
39 	   (X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives
48  * (16-byte) granularity, and we must ensure that no access straddles this
60 	   byte we calculate the length from the 2 8-byte words using
66 	   using the fast NUL check.  If we encounter non-ASCII characters,
76 	   checking for larger page sizes - the cost of setting up the correct
83 	and	tmp1, srcin, MIN_PAGE_SIZE - 1
85 	cmp	tmp1, MIN_PAGE_SIZE - 16
89 	/* For big-endian, carry propagation (if the final byte in the
91 	   Since we expect strings to be small and early-exit,
92 	   byte-swap the data now so has_null1/2 will be correct.  */
107 	mov	len, 8
110 	csel	len, xzr, len, cc
111 	add	len, len, tmp1, lsr 3
115 	   NUL check.  If we encounter non-ASCII characters, use a second
148 	/* For big-endian, carry propagation (if the final byte in the
150 	   easiest way to get the correct byte is to byte-swap the data
160 	sub	len, src, srcin
162 	add	tmp2, len, 8
164 	csel	len, len, tmp2, cc
165 	add	len, len, tmp1, lsr 3
196 	mov	tmp4, -1
198 	/* Big-endian.	Early bytes are at MSB.	 */
201 	/* Little-endian.  Early bytes are at LSB.  */