1/* Optimized strnlen implementation for PowerPC64/POWER7 using cmpb insn.
2   Copyright (C) 2010-2022 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
5   The GNU C Library is free software; you can redistribute it and/or
6   modify it under the terms of the GNU Lesser General Public
7   License as published by the Free Software Foundation; either
8   version 2.1 of the License, or (at your option) any later version.
9
10   The GNU C Library is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public
16   License along with the GNU C Library; if not, see
17   <https://www.gnu.org/licenses/>.  */
18
19#include <sysdep.h>
20
21#ifndef STRNLEN
22# define STRNLEN __strnlen
23#endif
24
25/* int [r3] strnlen (char *s [r3], int size [r4])  */
26	.machine  power7
27ENTRY_TOCLESS (STRNLEN)
28	CALL_MCOUNT 2
29	dcbt	0,r3
30	clrrdi	r8,r3,3
31	add	r7,r3,r4      /* Calculate the last acceptable address.  */
32	cmpldi	r4,32
33	li	r0,0	      /* Doubleword with null chars.  */
34	addi	r7,r7,-1
35
36	/* If we have less than 33 bytes to search, skip to a faster code.  */
37	ble	L(small_range)
38
39	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
40	ld	r12,0(r8)     /* Load doubleword from memory.  */
41	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
42#ifdef __LITTLE_ENDIAN__
43	srd	r10,r10,r6
44	sld	r10,r10,r6
45#else
46	sld	r10,r10,r6
47	srd	r10,r10,r6
48#endif
49	cmpldi	cr7,r10,0     /* If r10 == 0, no null's have been found.  */
50	bne	cr7,L(done)
51
52	clrrdi	r7,r7,3       /* Address of last doubleword.  */
53	mtcrf   0x01,r8
54	/* Are we now aligned to a quadword boundary?  If so, skip to
55	   the main loop.  Otherwise, go through the alignment code.  */
56
57	bt	28,L(loop_setup)
58
59	/* Handle DWORD2 of pair.  */
60	ldu	r12,8(r8)
61	cmpb	r10,r12,r0
62	cmpldi	cr7,r10,0
63	bne	cr7,L(done)
64
65L(loop_setup):
66	/* The last dword we want to read in the loop below is the one
67	   containing the last byte of the string, ie. the dword at
68	   (s + size - 1) & ~7, or r7.  The first dword read is at
69	   r8 + 8, we read 2 * cnt dwords, so the last dword read will
70	   be at r8 + 8 + 16 * cnt - 8.  Solving for cnt gives
71	   cnt = (r7 - r8) / 16  */
72	sub	r5,r7,r8
73	srdi	r6,r5,4	      /* Number of loop iterations.  */
74	mtctr	r6	      /* Setup the counter.  */
75
76	/* Main loop to look for the null byte in the string.  Since
77	   it's a small loop (< 8 instructions), align it to 32-bytes.  */
78	.p2align  5
79L(loop):
80	/* Load two doublewords, compare and merge in a
81	   single register for speed.  This is an attempt
82	   to speed up the null-checking process for bigger strings.  */
83
84	ld	r12,8(r8)
85	ldu	r11,16(r8)
86	cmpb	r10,r12,r0
87	cmpb	r9,r11,r0
88	or	r5,r9,r10     /* Merge everything in one doubleword.  */
89	cmpldi	cr7,r5,0
90	bne	cr7,L(found)
91	bdnz	L(loop)
92
93	/* We may have one more dword to read.  */
94	cmpld	cr6,r8,r7
95	beq	cr6,L(end_max)
96
97	ldu	r12,8(r8)
98	cmpb	r10,r12,r0
99	cmpldi	cr6,r10,0
100	bne	cr6,L(done)
101
102L(end_max):
103	mr	r3,r4
104	blr
105
106	/* OK, one (or both) of the doublewords contains a null byte.  Check
107	   the first doubleword and decrement the address in case the first
108	   doubleword really contains a null byte.  */
109	.align	4
110L(found):
111	cmpldi	cr6,r10,0
112	addi	r8,r8,-8
113	bne	cr6,L(done)
114
115	/* The null byte must be in the second doubleword.  Adjust the address
116	   again and move the result of cmpb to r10 so we can calculate the
117	   length.  */
118
119	mr	r10,r9
120	addi	r8,r8,8
121
122	/* r10 has the output of the cmpb instruction, that is, it contains
123	   0xff in the same position as the null byte in the original
124	   doubleword from the string.  Use that to calculate the length.
125	   We need to make sure the null char is *before* the end of the
126	   range.  */
127L(done):
128#ifdef __LITTLE_ENDIAN__
129	addi	r0,r10,-1
130	andc	r0,r0,r10
131	popcntd	r0,r0
132#else
133	cntlzd	r0,r10	      /* Count leading zeros before the match.  */
134#endif
135	sub	r3,r8,r3
136	srdi	r0,r0,3	      /* Convert leading/trailing zeros to bytes.  */
137	add	r3,r3,r0      /* Length until the match.  */
138	cmpld	r3,r4
139	blelr
140	mr	r3,r4
141	blr
142
143/* Deals with size <= 32.  */
144	.align	4
145L(small_range):
146	cmpldi	r4,0
147	beq	L(end_max)
148
149	clrrdi	r7,r7,3       /* Address of last doubleword.  */
150
151	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
152	ld	r12,0(r8)     /* Load doubleword from memory.  */
153	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
154#ifdef __LITTLE_ENDIAN__
155	srd	r10,r10,r6
156	sld	r10,r10,r6
157#else
158	sld	r10,r10,r6
159	srd	r10,r10,r6
160#endif
161	cmpldi	cr7,r10,0
162	bne	cr7,L(done)
163
164	cmpld	r8,r7
165	beq	L(end_max)
166
167	.p2align  5
168L(loop_small):
169	ldu	r12,8(r8)
170	cmpb	r10,r12,r0
171	cmpldi	cr6,r10,0
172	bne	cr6,L(done)
173	cmpld	r8,r7
174	bne	L(loop_small)
175	mr	r3,r4
176	blr
177
178END (STRNLEN)
179libc_hidden_def (__strnlen)
180weak_alias (__strnlen, strnlen)
181libc_hidden_def (strnlen)
182