1/* Optimized strnlen implementation for PowerPC64/POWER7 using cmpb insn.
2 Copyright (C) 2010-2024 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

source code of glibc/sysdeps/powerpc/powerpc64/power7/strnlen.S