1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * strlen() for PPC32
4 *
5 * Copyright (C) 2018 Christophe Leroy CS Syst
6 *
7 * Inspired from glibc implementation
8 */
9 #include <linux/export.h>
10 #include <asm/ppc_asm.h>
11 #include <asm/cache.h>
12
13 .text
14
15 /*
16 * Algorithm:
17 *
18 * 1) Given a word 'x', we can test to see if
19 * by subtracting 0x01010101, and seeing if
20 * byte changed from 0 to 1. This works bec
21 * 0 byte must have had no incoming carry (
22 * significant), so it is 0x00 - 0x01 == 0x
23 * byte values, either they have the high b
24 * 1 is subtracted you get a value in the r
25 * have their high bit set. The expression
26 * (x - 0x01010101) & ~x & 0x80808080), whi
27 * there were no 0x00 bytes in the word. Y
28 * match, but possibly false 0x80 matches i
29 * byte to a true match due to carries. Fo
30 * of no consequence since the least signif
31 * we're interested in, but big-endian need
32 * byte matches.
33 * 2) Given a word 'x', we can test to see _wh
34 * calculating ~(((x & ~0x80808080) - 0x808
35 * This produces 0x80 in each byte that was
36 * the other bytes. The '| ~0x80808080' cle
37 * byte, and the '| x' part ensures that by
38 * produce 0x00. The addition will carry in
39 * iff that byte had one of its low 7 bits
40 * which was the most significant bit set a
41 * many to add to the index.
42 * This is from the book 'The PowerPC Compi
43 * by Steve Hoxey, Faraydon Karim, Bill Hay
44 */
45
46 _GLOBAL(strlen)
47 andi. r0, r3, 3
48 lis r7, 0x0101
49 addi r10, r3, -4
50 addic r7, r7, 0x0101 /* r7 = 0x0101
51 rotlwi r6, r7, 31 /* r6 = 0x8080
52 bne- 3f
53 .balign IFETCH_ALIGN_BYTES
54 1: lwzu r9, 4(r10)
55 2: subf r8, r7, r9
56 and. r8, r8, r6
57 beq+ 1b
58 andc. r8, r8, r9
59 beq+ 1b
60 andc r8, r9, r6
61 orc r9, r9, r6
62 subfe r8, r6, r8
63 nor r8, r8, r9
64 cntlzw r8, r8
65 subf r3, r3, r10
66 srwi r8, r8, 3
67 add r3, r3, r8
68 blr
69
70 /* Missaligned string: make sure bytes
71 3: xor r10, r10, r0
72 orc r8, r8, r8
73 lwzu r9, 4(r10)
74 slwi r0, r0, 3
75 srw r8, r8, r0
76 orc r9, r9, r8
77 b 2b
78 EXPORT_SYMBOL(strlen)
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