1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18 #include <stdint.h>
19 #include <string-fzb.h>
20 #include <string-fzc.h>
21 #include <string-fzi.h>
22 #include <string.h>
23 #include <memcopy.h>
24
25 #ifdef STRCMP
26 # define strcmp STRCMP
27 #endif
28
29 static inline int
30 final_cmp (const op_t w1, const op_t w2)
31 {
32 unsigned int idx = index_first_zero_ne (w1, w2);
33 return extractbyte (w1, idx) - extractbyte (w2, idx);
34 }
35
36 /* Aligned loop: if a difference is found, exit to compare the bytes. Else
37 if a zero is found we have equal strings. */
38 static inline int
39 strcmp_aligned_loop (const op_t *x1, const op_t *x2, op_t w1)
40 {
41 op_t w2 = *x2++;
42
43 while (w1 == w2)
44 {
45 if (has_zero (w1))
46 return 0;
47 w1 = *x1++;
48 w2 = *x2++;
49 }
50
51 return final_cmp (w1, w2);
52 }
53
54 /* Unaligned loop: align the first partial of P2, with 0xff for the rest of
55 the bytes so that we can also apply the has_zero test to see if we have
56 already reached EOS. If we have, then we can simply fall through to the
57 final comparison. */
58 static inline int
59 strcmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs)
60 {
61 op_t w2a = *x2++;
62 uintptr_t sh_1 = ofs * CHAR_BIT;
63 uintptr_t sh_2 = sizeof(op_t) * CHAR_BIT - sh_1;
64
65 op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2);
66 if (!has_zero (w2))
67 {
68 op_t w2b;
69
70 /* Unaligned loop. The invariant is that W2B, which is "ahead" of W1,
71 does not contain end-of-string. Therefore it is safe (and necessary)
72 to read another word from each while we do not have a difference. */
73 while (1)
74 {
75 w2b = *x2++;
76 w2 = MERGE (w2a, sh_1, w2b, sh_2);
77 if (w1 != w2)
78 return final_cmp (w1, w2);
79 if (has_zero (w2b))
80 break;
81 w1 = *x1++;
82 w2a = w2b;
83 }
84
85 /* Zero found in the second partial of P2. If we had EOS in the aligned
86 word, we have equality. */
87 if (has_zero (w1))
88 return 0;
89
90 /* Load the final word of P1 and align the final partial of P2. */
91 w1 = *x1++;
92 w2 = MERGE (w2b, sh_1, 0, sh_2);
93 }
94
95 return final_cmp (w1, w2);
96 }
97
98 /* Compare S1 and S2, returning less than, equal to or
99 greater than zero if S1 is lexicographically less than,
100 equal to or greater than S2. */
101 int
102 strcmp (const char *p1, const char *p2)
103 {
104 /* Handle the unaligned bytes of p1 first. */
105 uintptr_t n = -(uintptr_t)p1 % sizeof(op_t);
106 for (int i = 0; i < n; ++i)
107 {
108 unsigned char c1 = *p1++;
109 unsigned char c2 = *p2++;
110 int diff = c1 - c2;
111 if (c1 == '\0' || diff != 0)
112 return diff;
113 }
114
115 /* P1 is now aligned to op_t. P2 may or may not be. */
116 const op_t *x1 = (const op_t *) p1;
117 op_t w1 = *x1++;
118 uintptr_t ofs = (uintptr_t) p2 % sizeof(op_t);
119 return ofs == 0
120 ? strcmp_aligned_loop (x1, (const op_t *)p2, w1)
121 : strcmp_unaligned_loop (x1, (const op_t *)(p2 - ofs), w1, ofs);
122 }
123 #ifndef STRCMP
124 libc_hidden_builtin_def (strcmp)
125 #endif