1 /* SPDX-License-Identifier: GPL-2.0-only */
2
3 #include <linux/linkage.h>
4 #include <asm/asm.h>
5 #include <asm/alternative-macros.h>
6 #include <asm/hwcap.h>
7
8 /* int strcmp(const char *cs, const char *ct) */
9 SYM_FUNC_START(strcmp)
10
11 ALTERNATIVE("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
12
13 /*
14 * Returns
15 * a0 - comparison result, value like strcmp
16 *
17 * Parameters
18 * a0 - string1
19 * a1 - string2
20 *
21 * Clobbers
22 * t0, t1
23 */
24 1:
25 lbu t0, 0(a0)
26 lbu t1, 0(a1)
27 addi a0, a0, 1
28 addi a1, a1, 1
29 bne t0, t1, 2f
30 bnez t0, 1b
31 li a0, 0
32 ret
33 2:
34 /*
35 * strcmp only needs to return (< 0, 0, > 0) values
36 * not necessarily -1, 0, +1
37 */
38 sub a0, t0, t1
39 ret
40
41 /*
42 * Variant of strcmp using the ZBB extension if available.
43 * The code was published as part of the bitmanip manual
44 * in Appendix A.
45 */
46 #ifdef CONFIG_RISCV_ISA_ZBB
47 strcmp_zbb:
48
49 .option push
50 .option arch,+zbb
51
52 /*
53 * Returns
54 * a0 - comparison result, value like strcmp
55 *
56 * Parameters
57 * a0 - string1
58 * a1 - string2
59 *
60 * Clobbers
61 * t0, t1, t2, t3, t4
62 */
63
64 or t2, a0, a1
65 li t4, -1
66 and t2, t2, SZREG-1
67 bnez t2, 3f
68
69 /* Main loop for aligned string. */
70 .p2align 3
71 1:
72 REG_L t0, 0(a0)
73 REG_L t1, 0(a1)
74 orc.b t3, t0
75 bne t3, t4, 2f
76 addi a0, a0, SZREG
77 addi a1, a1, SZREG
78 beq t0, t1, 1b
79
80 /*
81 * Words don't match, and no null byte in the first
82 * word. Get bytes in big-endian order and compare.
83 */
84 #ifndef CONFIG_CPU_BIG_ENDIAN
85 rev8 t0, t0
86 rev8 t1, t1
87 #endif
88
89 /* Synthesize (t0 >= t1) ? 1 : -1 in a branchless sequence. */
90 sltu a0, t0, t1
91 neg a0, a0
92 ori a0, a0, 1
93 ret
94
95 2:
96 /*
97 * Found a null byte.
98 * If words don't match, fall back to simple loop.
99 */
100 bne t0, t1, 3f
101
102 /* Otherwise, strings are equal. */
103 li a0, 0
104 ret
105
106 /* Simple loop for misaligned strings. */
107 .p2align 3
108 3:
109 lbu t0, 0(a0)
110 lbu t1, 0(a1)
111 addi a0, a0, 1
112 addi a1, a1, 1
113 bne t0, t1, 4f
114 bnez t0, 3b
115
116 4:
117 sub a0, t0, t1
118 ret
119
120 .option pop
121 #endif
122 SYM_FUNC_END(strcmp)
123 SYM_FUNC_ALIAS(__pi_strcmp, strcmp)
124 EXPORT_SYMBOL(strcmp)
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