summaryrefslogtreecommitdiff
path: root/sysdeps/x86_64/strlen.S
blob: 9203dc0c39c4ad6afc739616f3582c6245a2b0b8 (plain)
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
/* SSE2 version of strlen.
   Copyright (C) 2012-2014 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
   <http://www.gnu.org/licenses/>.  */

#include <sysdep.h>

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

	%xmm11 - 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	\
	pcmpeqb	(%rax), %xmm8;	\
	pcmpeqb	16(%rax), %xmm9;	\
	pcmpeqb	32(%rax), %xmm10;	\
	pcmpeqb	48(%rax), %xmm11;	\
	pmovmskb	%xmm8, %esi;	\
	pmovmskb	%xmm9, %edx;	\
	pmovmskb	%xmm10, %r8d;	\
	pmovmskb	%xmm11, %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, %rsi
	jne	L(n_nonzero)
	xor	%rax, %rax
	ret
L(n_nonzero):

/* Initialize long lived registers.  */

	add	%rdi, %rsi
	mov	%rsi, %r10
	and	$-64, %r10
	mov	%rsi, %r11
#endif

	pxor	%xmm8, %xmm8
	pxor	%xmm9, %xmm9
	pxor	%xmm10, %xmm10
	pxor	%xmm11, %xmm11
	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;	\
	ret

#ifdef AS_STRNLEN
	andq	$-16, %rax
	FIND_ZERO
#else
	/* Test first 16 bytes unaligned.  */
	movdqu	(%rax), %xmm12
	pcmpeqb	%xmm8, %xmm12
	pmovmskb	%xmm12, %edx
	test	%edx, %edx
	je 	L(next48_bytes)
	bsf	%edx, %eax /* If eax is zeroed 16bit bsf can be used.  */
	ret

L(next48_bytes):
/* Same as FIND_ZERO except we do not check first 16 bytes.  */
	andq	$-16, %rax
	pcmpeqb 16(%rax), %xmm9
	pcmpeqb 32(%rax), %xmm10
	pcmpeqb 48(%rax), %xmm11
	pmovmskb	%xmm9, %edx
	pmovmskb	%xmm10, %r8d
	pmovmskb	%xmm11, %ecx
	salq	$16, %rdx
	salq	$16, %rcx
	orq	%r8, %rcx
	salq	$32, %rcx
	orq	%rcx, %rdx
#endif

	/* When no zero byte is found xmm9-11 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
	ret
#endif
	.p2align 4
L(loop_init):
	pxor	%xmm9, %xmm9
	pxor	%xmm10, %xmm10
	pxor	%xmm11, %xmm11
#ifdef AS_STRNLEN
	.p2align 4
L(loop):

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

	movdqa	(%rax), %xmm8
	pminub	16(%rax), %xmm8
	pminub	32(%rax), %xmm8
	pminub	48(%rax), %xmm8
	pcmpeqb	%xmm11, %xmm8
	pmovmskb	%xmm8, %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	%xmm8, %xmm8
	FIND_ZERO

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

	.p2align 4
L(exit):
	pxor	%xmm8, %xmm8
	FIND_ZERO

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

#else

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

	movdqa	64(%rax), %xmm8
	pminub	80(%rax), %xmm8
	pminub	96(%rax), %xmm8
	pminub	112(%rax), %xmm8
	pcmpeqb	%xmm11, %xmm8
	pmovmskb	%xmm8, %edx
	testl	%edx, %edx
	jne	L(exit64)

	subq	$-128, %rax

	movdqa	(%rax), %xmm8
	pminub	16(%rax), %xmm8
	pminub	32(%rax), %xmm8
	pminub	48(%rax), %xmm8
	pcmpeqb	%xmm11, %xmm8
	pmovmskb	%xmm8, %edx
	testl	%edx, %edx
	jne	L(exit0)
	jmp	L(loop)

	.p2align 4
L(exit64):
	addq	$64, %rax
L(exit0):
	pxor	%xmm8, %xmm8
	FIND_ZERO

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

#endif

END(strlen)
libc_hidden_builtin_def (strlen)