1/* strspn with SSE4.2 intrinsics
2 Copyright (C) 2009-2022 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 <nmmintrin.h>
20#include <string.h>
21#include "varshift.h"
22
23/* We use 0x12:
24 _SIDD_SBYTE_OPS
25 | _SIDD_CMP_EQUAL_ANY
26 | _SIDD_NEGATIVE_POLARITY
27 | _SIDD_LEAST_SIGNIFICANT
28 on pcmpistri to compare xmm/mem128
29
30 0 1 2 3 4 5 6 7 8 9 A B C D E F
31 X X X X X X X X X X X X X X X X
32
33 against xmm
34
35 0 1 2 3 4 5 6 7 8 9 A B C D E F
36 A A A A A A A A A A A A A A A A
37
38 to find out if the first 16byte data element has any non-A byte and
39 the offset of the first byte. There are 2 cases:
40
41 1. The first 16byte data element has the non-A byte, including
42 EOS, at the offset X.
43 2. The first 16byte data element is valid and doesn't have the non-A
44 byte.
45
46 Here is the table of ECX, CFlag, ZFlag and SFlag for 2 cases:
47
48 case ECX CFlag ZFlag SFlag
49 1 X 1 0/1 0
50 2 16 0 0 0
51
52 We exit from the loop for case 1. */
53
54extern size_t __strspn_sse2 (const char *, const char *) attribute_hidden;
55
56
57size_t
58__attribute__ ((section (".text.sse4.2")))
59__strspn_sse42 (const char *s, const char *a)
60{
61 if (*a == 0)
62 return 0;
63
64 const char *aligned;
65 __m128i mask, maskz, zero;
66 unsigned int maskz_bits;
67 unsigned int offset = (int) ((size_t) a & 15);
68 zero = _mm_set1_epi8 (b: 0);
69 if (offset != 0)
70 {
71 /* Load masks. */
72 aligned = (const char *) ((size_t) a & -16L);
73 __m128i mask0 = _mm_load_si128 (p: (__m128i *) aligned);
74 maskz = _mm_cmpeq_epi8 (a: mask0, b: zero);
75
76 /* Find where the NULL terminator is. */
77 maskz_bits = _mm_movemask_epi8 (a: maskz) >> offset;
78 if (maskz_bits != 0)
79 {
80 mask = __m128i_shift_right (value: mask0, offset);
81 offset = (unsigned int) ((size_t) s & 15);
82 if (offset)
83 goto start_unaligned;
84
85 aligned = s;
86 goto start_loop;
87 }
88 }
89
90 /* A is aligned. */
91 mask = _mm_loadu_si128 (p: (__m128i *) a);
92
93 /* Find where the NULL terminator is. */
94 maskz = _mm_cmpeq_epi8 (a: mask, b: zero);
95 maskz_bits = _mm_movemask_epi8 (a: maskz);
96 if (maskz_bits == 0)
97 {
98 /* There is no NULL terminator. Don't use SSE4.2 if the length
99 of A > 16. */
100 if (a[16] != 0)
101 return __strspn_sse2 (s, a);
102 }
103 aligned = s;
104 offset = (unsigned int) ((size_t) s & 15);
105
106 if (offset != 0)
107 {
108 start_unaligned:
109 /* Check partial string. */
110 aligned = (const char *) ((size_t) s & -16L);
111 __m128i value = _mm_load_si128 (p: (__m128i *) aligned);
112 __m128i adj_value = __m128i_shift_right (value, offset);
113
114 unsigned int length = _mm_cmpistri (mask, adj_value, 0x12);
115 /* No need to check CFlag since it is always 1. */
116 if (length < 16 - offset)
117 return length;
118 /* Find where the NULL terminator is. */
119 maskz = _mm_cmpeq_epi8 (a: value, b: zero);
120 maskz_bits = _mm_movemask_epi8 (a: maskz) >> offset;
121 if (maskz_bits != 0)
122 return length;
123 aligned += 16;
124 }
125
126start_loop:
127 while (1)
128 {
129 __m128i value = _mm_load_si128 (p: (__m128i *) aligned);
130 unsigned int index = _mm_cmpistri (mask, value, 0x12);
131 unsigned int cflag = _mm_cmpistrc (mask, value, 0x12);
132 if (cflag)
133 return (size_t) (aligned + index - s);
134 aligned += 16;
135 }
136}
137

source code of glibc/sysdeps/x86_64/multiarch/strspn-c.c