1/*
2 * __strcmp_aarch64_sve - compare two strings
3 *
4 * Copyright (c) 2018-2022, Arm Limited.
5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
6 */
7
8#include "asmdefs.h"
9
10#if __ARM_FEATURE_SVE
11/* Assumptions:
12 *
13 * ARMv8-a, AArch64
14 * SVE Available.
15 */
16
17ENTRY (__strcmp_aarch64_sve)
18	PTR_ARG (0)
19	PTR_ARG (1)
20	setffr				/* initialize FFR */
21	ptrue	p1.b, all		/* all ones; loop invariant */
22	mov	x2, 0			/* initialize offset */
23
24	/* Read a vector's worth of bytes, stopping on first fault.  */
25	.p2align 4
260:	ldff1b	z0.b, p1/z, [x0, x2]
27	ldff1b	z1.b, p1/z, [x1, x2]
28	rdffrs	p0.b, p1/z
29	b.nlast	2f
30
31	/* First fault did not fail: the whole vector is valid.
32	   Avoid depending on the contents of FFR beyond the branch.  */
33	incb	x2, all			/* skip bytes for next round */
34	cmpeq	p2.b, p1/z, z0.b, z1.b	/* compare strings */
35	cmpne	p3.b, p1/z, z0.b, 0	/* search for ~zero */
36	nands	p2.b, p1/z, p2.b, p3.b	/* ~(eq & ~zero) -> ne | zero */
37	b.none	0b
38
39	/* Found end-of-string or inequality.  */
401:	brkb	p2.b, p1/z, p2.b	/* find first such */
41	lasta	w0, p2, z0.b		/* extract each char */
42	lasta	w1, p2, z1.b
43	sub	x0, x0, x1		/* return comparison */
44	ret
45
46	/* First fault failed: only some of the vector is valid.
47	   Perform the comparison only on the valid bytes.  */
482:	incp	x2, p0.b		/* skip bytes for next round */
49	setffr				/* re-init FFR for next round */
50	cmpeq	p2.b, p0/z, z0.b, z1.b	/* compare strings, as above */
51	cmpne	p3.b, p0/z, z0.b, 0
52	nands	p2.b, p0/z, p2.b, p3.b
53	b.none	0b
54	b	1b
55
56END (__strcmp_aarch64_sve)
57
58#endif
59
60