summary refs log tree commit diff
path: root/sysdeps/x86_64/strlen.S
blob: 2e226d0d55e84e67f76a6affc802a2f73b1097eb (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
/* SSE2 version of strlen/wcslen.
   Copyright (C) 2012-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>

#ifdef AS_WCSLEN
# define PMINU		pminud
# define PCMPEQ		pcmpeqd
# define SHIFT_RETURN	shrq $2, %rax
#else
# define PMINU		pminub
# define PCMPEQ		pcmpeqb
# define SHIFT_RETURN
#endif

/* Long lived register in strlen(s), strnlen(s, n) are:

	%xmm3 - zero
	%rdi   - s
	%r10  (s+n) & (~(64-1))
	%r11   s+n
*/


.text
ENTRY(strlen)

/* Test 64 bytes from %rax for zero. Save result as bitmask in %rdx.  */
#define FIND_ZERO	\
	PCMPEQ	(%rax), %xmm0;	\
	PCMPEQ	16(%rax), %xmm1;	\
	PCMPEQ	32(%rax), %xmm2;	\
	PCMPEQ	48(%rax), %xmm3;	\
	pmovmskb	%xmm0, %esi;	\
	pmovmskb	%xmm1, %edx;	\
	pmovmskb	%xmm2, %r8d;	\
	pmovmskb	%xmm3, %ecx;	\
	salq	$16, %rdx;	\
	salq	$16, %rcx;	\
	orq	%rsi, %rdx;	\
	orq	%r8, %rcx;	\
	salq	$32, %rcx;	\
	orq	%rcx, %rdx;

#ifdef AS_STRNLEN
/* Do not read anything when n==0.  */
	test	%RSI_LP, %RSI_LP
	jne	L(n_nonzero)
	xor	%rax, %rax
	ret
L(n_nonzero):
# ifdef AS_WCSLEN
	shl	$2, %RSI_LP
# endif

/* Initialize long lived registers.  */

	add	%RDI_LP, %RSI_LP
	mov	%RSI_LP, %R10_LP
	and	$-64, %R10_LP
	mov	%RSI_LP, %R11_LP
#endif

	pxor	%xmm0, %xmm0
	pxor	%xmm1, %xmm1
	pxor	%xmm2, %xmm2
	pxor	%xmm3, %xmm3
	movq	%rdi, %rax
	movq	%rdi, %rcx
	andq	$4095, %rcx
/* Offsets 4032-4047 will be aligned into 4032 thus fit into page.  */
	cmpq	$4047, %rcx
/* We cannot unify this branching as it would be ~6 cycles slower.  */
	ja	L(cross_page)

#ifdef AS_STRNLEN
/* Test if end is among first 64 bytes.  */
# define STRNLEN_PROLOG	\
	mov	%r11, %rsi;	\
	subq	%rax, %rsi;	\
	andq	$-64, %rax;	\
	testq	$-64, %rsi;	\
	je	L(strnlen_ret)
#else
# define STRNLEN_PROLOG  andq $-64, %rax;
#endif

/* Ignore bits in mask that come before start of string.  */
#define PROLOG(lab)	\
	movq	%rdi, %rcx;	\
	xorq	%rax, %rcx;	\
	STRNLEN_PROLOG;	\
	sarq	%cl, %rdx;	\
	test	%rdx, %rdx;	\
	je	L(lab);	\
	bsfq	%rdx, %rax;	\
	SHIFT_RETURN;		\
	ret

#ifdef AS_STRNLEN
	andq	$-16, %rax
	FIND_ZERO
#else
	/* Test first 16 bytes unaligned.  */
	movdqu	(%rax), %xmm4
	PCMPEQ	%xmm0, %xmm4
	pmovmskb	%xmm4, %edx
	test	%edx, %edx
	je 	L(next48_bytes)
	bsf	%edx, %eax /* If eax is zeroed 16bit bsf can be used.  */
	SHIFT_RETURN
	ret

L(next48_bytes):
/* Same as FIND_ZERO except we do not check first 16 bytes.  */
	andq	$-16, %rax
	PCMPEQ 16(%rax), %xmm1
	PCMPEQ 32(%rax), %xmm2
	PCMPEQ 48(%rax), %xmm3
	pmovmskb	%xmm1, %edx
	pmovmskb	%xmm2, %r8d
	pmovmskb	%xmm3, %ecx
	salq	$16, %rdx
	salq	$16, %rcx
	orq	%r8, %rcx
	salq	$32, %rcx
	orq	%rcx, %rdx
#endif

	/* When no zero byte is found xmm1-3 are zero so we do not have to
	   zero them.  */
	PROLOG(loop)

	.p2align 4
L(cross_page):
	andq	$-64, %rax
	FIND_ZERO
	PROLOG(loop_init)

#ifdef AS_STRNLEN
/* We must do this check to correctly handle strnlen (s, -1).  */
L(strnlen_ret):
	bts	%rsi, %rdx
	sarq	%cl, %rdx
	test	%rdx, %rdx
	je	L(loop_init)
	bsfq	%rdx, %rax
	SHIFT_RETURN
	ret
#endif
	.p2align 4
L(loop_init):
	pxor	%xmm1, %xmm1
	pxor	%xmm2, %xmm2
	pxor	%xmm3, %xmm3
#ifdef AS_STRNLEN
	.p2align 4
L(loop):

	addq	$64, %rax
	cmpq	%rax, %r10
	je	L(exit_end)

	movdqa	(%rax), %xmm0
	PMINU	16(%rax), %xmm0
	PMINU	32(%rax), %xmm0
	PMINU	48(%rax), %xmm0
	PCMPEQ	%xmm3, %xmm0
	pmovmskb	%xmm0, %edx
	testl	%edx, %edx
	jne	L(exit)
	jmp	L(loop)

	.p2align 4
L(exit_end):
	cmp	%rax, %r11
	je	L(first) /* Do not read when end is at page boundary.  */
	pxor	%xmm0, %xmm0
	FIND_ZERO

L(first):
	bts	%r11, %rdx
	bsfq	%rdx, %rdx
	addq	%rdx, %rax
	subq	%rdi, %rax
	SHIFT_RETURN
	ret

	.p2align 4
L(exit):
	pxor	%xmm0, %xmm0
	FIND_ZERO

	bsfq	%rdx, %rdx
	addq	%rdx, %rax
	subq	%rdi, %rax
	SHIFT_RETURN
	ret

#else

	/* Main loop.  Unrolled twice to improve L2 cache performance on core2.  */
	.p2align 4
L(loop):

	movdqa	64(%rax), %xmm0
	PMINU	80(%rax), %xmm0
	PMINU	96(%rax), %xmm0
	PMINU	112(%rax), %xmm0
	PCMPEQ	%xmm3, %xmm0
	pmovmskb	%xmm0, %edx
	testl	%edx, %edx
	jne	L(exit64)

	subq	$-128, %rax

	movdqa	(%rax), %xmm0
	PMINU	16(%rax), %xmm0
	PMINU	32(%rax), %xmm0
	PMINU	48(%rax), %xmm0
	PCMPEQ	%xmm3, %xmm0
	pmovmskb	%xmm0, %edx
	testl	%edx, %edx
	jne	L(exit0)
	jmp	L(loop)

	.p2align 4
L(exit64):
	addq	$64, %rax
L(exit0):
	pxor	%xmm0, %xmm0
	FIND_ZERO

	bsfq	%rdx, %rdx
	addq	%rdx, %rax
	subq	%rdi, %rax
	SHIFT_RETURN
	ret

#endif

END(strlen)
libc_hidden_builtin_def (strlen)