1/* Optimized version of the standard strlen() function.
2 This file is part of the GNU C Library.
3 Copyright (C) 2000-2022 Free Software Foundation, Inc.
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/* Return: the length of the input string
20
21 Input:
22 in0: str
23
24 Look for the null character byte by byte, until we reach a word aligned
25 address, then search word by word, using the czx instruction. We're
26 also doing one word of read ahead, which could cause problems if the
27 null character is on the last word of a page and the next page is not
28 mapped in the process address space. Hence the use of the speculative
29 load.
30
31 This implementation assumes little endian mode. For big endian mode,
32 the instruction czx1.r should be replaced by czx1.l. */
33
34#include <sysdep.h>
35#undef ret
36
37#define saved_lc r18
38#define str r19
39#define pos0 r20
40#define val1 r21
41#define val2 r22
42#define origadd r23
43#define tmp r24
44#define loopcnt r30
45#define len ret0
46
47ENTRY(strlen)
48 .prologue
49 alloc r2 = ar.pfs, 1, 0, 0, 0
50 .save ar.lc, saved_lc
51 mov saved_lc = ar.lc // save the loop counter
52 .body
53 mov str = in0
54 mov len = r0 // len = 0
55 and tmp = 7, in0 // tmp = str % 8
56 ;;
57 sub loopcnt = 8, tmp // loopcnt = 8 - tmp
58 cmp.eq p6, p0 = tmp, r0
59(p6) br.cond.sptk .str_aligned;;
60 adds loopcnt = -1, loopcnt;;
61 mov ar.lc = loopcnt
62.l1:
63 ld1 val2 = [str], 1
64 ;;
65 cmp.eq p6, p0 = val2, r0
66(p6) br.cond.spnt .restore_and_exit
67 adds len = 1, len
68 br.cloop.dptk .l1
69.str_aligned:
70 mov origadd = str // origadd = orig
71 ld8 val1 = [str], 8;;
72 nop.b 0
73 nop.b 0
74.l2: ld8.s val2 = [str], 8 // don't bomb out here
75 czx1.r pos0 = val1
76 ;;
77 cmp.ne p6, p0 = 8, pos0
78(p6) br.cond.spnt .foundit
79 chk.s val2, .recovery
80.back:
81 mov val1 = val2
82 br.cond.dptk .l2
83.foundit:
84 sub tmp = str, origadd // tmp = crt address - orig
85 add len = len, pos0;;
86 add len = len, tmp;;
87 adds len = -16, len
88.restore_and_exit:
89 mov ar.lc = saved_lc // restore the loop counter
90 br.ret.sptk.many b0
91.recovery:
92 adds str = -8, str;;
93 ld8 val2 = [str], 8 // bomb out here
94 br.cond.sptk .back
95END(strlen)
96libc_hidden_builtin_def (strlen)
97

source code of glibc/sysdeps/ia64/strlen.S