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zhichang.yuan192c4d92014-04-28 13:11:33 +08001/*
2 * Copyright (C) 2013 ARM Ltd.
3 * Copyright (C) 2013 Linaro.
4 *
5 * This code is based on glibc cortex strings work originally authored by Linaro
6 * and re-licensed under GPLv2 for the Linux kernel. The original code can
7 * be found @
8 *
9 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
10 * files/head:/src/aarch64/
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2 as
14 * published by the Free Software Foundation.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program. If not, see <http://www.gnu.org/licenses/>.
23 */
24
25#include <linux/linkage.h>
26#include <asm/assembler.h>
27
28/*
29 * compare two strings
30 *
31 * Parameters:
32 * x0 - const string 1 pointer
33 * x1 - const string 2 pointer
34 * x2 - the maximal length to be compared
35 * Returns:
36 * x0 - an integer less than, equal to, or greater than zero if s1 is found,
37 * respectively, to be less than, to match, or be greater than s2.
38 */
39
40#define REP8_01 0x0101010101010101
41#define REP8_7f 0x7f7f7f7f7f7f7f7f
42#define REP8_80 0x8080808080808080
43
44/* Parameters and result. */
45src1 .req x0
46src2 .req x1
47limit .req x2
48result .req x0
49
50/* Internal variables. */
51data1 .req x3
52data1w .req w3
53data2 .req x4
54data2w .req w4
55has_nul .req x5
56diff .req x6
57syndrome .req x7
58tmp1 .req x8
59tmp2 .req x9
60tmp3 .req x10
61zeroones .req x11
62pos .req x12
63limit_wd .req x13
64mask .req x14
65endloop .req x15
66
67ENTRY(strncmp)
68 cbz limit, .Lret0
69 eor tmp1, src1, src2
70 mov zeroones, #REP8_01
71 tst tmp1, #7
72 b.ne .Lmisaligned8
73 ands tmp1, src1, #7
74 b.ne .Lmutual_align
75 /* Calculate the number of full and partial words -1. */
76 /*
77 * when limit is mulitply of 8, if not sub 1,
78 * the judgement of last dword will wrong.
79 */
80 sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
81 lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
82
83 /*
84 * NUL detection works on the principle that (X - 1) & (~X) & 0x80
85 * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
86 * can be done in parallel across the entire word.
87 */
88.Lloop_aligned:
89 ldr data1, [src1], #8
90 ldr data2, [src2], #8
91.Lstart_realigned:
92 subs limit_wd, limit_wd, #1
93 sub tmp1, data1, zeroones
94 orr tmp2, data1, #REP8_7f
95 eor diff, data1, data2 /* Non-zero if differences found. */
96 csinv endloop, diff, xzr, pl /* Last Dword or differences.*/
97 bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
98 ccmp endloop, #0, #0, eq
99 b.eq .Lloop_aligned
100
101 /*Not reached the limit, must have found the end or a diff. */
102 tbz limit_wd, #63, .Lnot_limit
103
104 /* Limit % 8 == 0 => all bytes significant. */
105 ands limit, limit, #7
106 b.eq .Lnot_limit
107
108 lsl limit, limit, #3 /* Bits -> bytes. */
109 mov mask, #~0
110CPU_BE( lsr mask, mask, limit )
111CPU_LE( lsl mask, mask, limit )
112 bic data1, data1, mask
113 bic data2, data2, mask
114
115 /* Make sure that the NUL byte is marked in the syndrome. */
116 orr has_nul, has_nul, mask
117
118.Lnot_limit:
119 orr syndrome, diff, has_nul
120 b .Lcal_cmpresult
121
122.Lmutual_align:
123 /*
124 * Sources are mutually aligned, but are not currently at an
125 * alignment boundary. Round down the addresses and then mask off
126 * the bytes that precede the start point.
127 * We also need to adjust the limit calculations, but without
128 * overflowing if the limit is near ULONG_MAX.
129 */
130 bic src1, src1, #7
131 bic src2, src2, #7
132 ldr data1, [src1], #8
133 neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */
134 ldr data2, [src2], #8
135 mov tmp2, #~0
136 sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
137 /* Big-endian. Early bytes are at MSB. */
138CPU_BE( lsl tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */
139 /* Little-endian. Early bytes are at LSB. */
140CPU_LE( lsr tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */
141
142 and tmp3, limit_wd, #7
143 lsr limit_wd, limit_wd, #3
144 /* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
145 add limit, limit, tmp1
146 add tmp3, tmp3, tmp1
147 orr data1, data1, tmp2
148 orr data2, data2, tmp2
149 add limit_wd, limit_wd, tmp3, lsr #3
150 b .Lstart_realigned
151
152/*when src1 offset is not equal to src2 offset...*/
153.Lmisaligned8:
154 cmp limit, #8
155 b.lo .Ltiny8proc /*limit < 8... */
156 /*
157 * Get the align offset length to compare per byte first.
158 * After this process, one string's address will be aligned.*/
159 and tmp1, src1, #7
160 neg tmp1, tmp1
161 add tmp1, tmp1, #8
162 and tmp2, src2, #7
163 neg tmp2, tmp2
164 add tmp2, tmp2, #8
165 subs tmp3, tmp1, tmp2
166 csel pos, tmp1, tmp2, hi /*Choose the maximum. */
167 /*
168 * Here, limit is not less than 8, so directly run .Ltinycmp
169 * without checking the limit.*/
170 sub limit, limit, pos
171.Ltinycmp:
172 ldrb data1w, [src1], #1
173 ldrb data2w, [src2], #1
174 subs pos, pos, #1
175 ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
176 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
177 b.eq .Ltinycmp
178 cbnz pos, 1f /*find the null or unequal...*/
179 cmp data1w, #1
180 ccmp data1w, data2w, #0, cs
181 b.eq .Lstart_align /*the last bytes are equal....*/
1821:
183 sub result, data1, data2
184 ret
185
186.Lstart_align:
187 lsr limit_wd, limit, #3
188 cbz limit_wd, .Lremain8
189 /*process more leading bytes to make str1 aligned...*/
190 ands xzr, src1, #7
191 b.eq .Lrecal_offset
192 add src1, src1, tmp3 /*tmp3 is positive in this branch.*/
193 add src2, src2, tmp3
194 ldr data1, [src1], #8
195 ldr data2, [src2], #8
196
197 sub limit, limit, tmp3
198 lsr limit_wd, limit, #3
199 subs limit_wd, limit_wd, #1
200
201 sub tmp1, data1, zeroones
202 orr tmp2, data1, #REP8_7f
203 eor diff, data1, data2 /* Non-zero if differences found. */
204 csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
205 bics has_nul, tmp1, tmp2
206 ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
207 b.ne .Lunequal_proc
208 /*How far is the current str2 from the alignment boundary...*/
209 and tmp3, tmp3, #7
210.Lrecal_offset:
211 neg pos, tmp3
212.Lloopcmp_proc:
213 /*
214 * Divide the eight bytes into two parts. First,backwards the src2
215 * to an alignment boundary,load eight bytes from the SRC2 alignment
216 * boundary,then compare with the relative bytes from SRC1.
217 * If all 8 bytes are equal,then start the second part's comparison.
218 * Otherwise finish the comparison.
219 * This special handle can garantee all the accesses are in the
220 * thread/task space in avoid to overrange access.
221 */
222 ldr data1, [src1,pos]
223 ldr data2, [src2,pos]
224 sub tmp1, data1, zeroones
225 orr tmp2, data1, #REP8_7f
226 bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
227 eor diff, data1, data2 /* Non-zero if differences found. */
228 csinv endloop, diff, xzr, eq
229 cbnz endloop, .Lunequal_proc
230
231 /*The second part process*/
232 ldr data1, [src1], #8
233 ldr data2, [src2], #8
234 subs limit_wd, limit_wd, #1
235 sub tmp1, data1, zeroones
236 orr tmp2, data1, #REP8_7f
237 eor diff, data1, data2 /* Non-zero if differences found. */
238 csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
239 bics has_nul, tmp1, tmp2
240 ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
241 b.eq .Lloopcmp_proc
242
243.Lunequal_proc:
244 orr syndrome, diff, has_nul
245 cbz syndrome, .Lremain8
246.Lcal_cmpresult:
247 /*
248 * reversed the byte-order as big-endian,then CLZ can find the most
249 * significant zero bits.
250 */
251CPU_LE( rev syndrome, syndrome )
252CPU_LE( rev data1, data1 )
253CPU_LE( rev data2, data2 )
254 /*
255 * For big-endian we cannot use the trick with the syndrome value
256 * as carry-propagation can corrupt the upper bits if the trailing
257 * bytes in the string contain 0x01.
258 * However, if there is no NUL byte in the dword, we can generate
259 * the result directly. We can't just subtract the bytes as the
260 * MSB might be significant.
261 */
262CPU_BE( cbnz has_nul, 1f )
263CPU_BE( cmp data1, data2 )
264CPU_BE( cset result, ne )
265CPU_BE( cneg result, result, lo )
266CPU_BE( ret )
267CPU_BE( 1: )
268 /* Re-compute the NUL-byte detection, using a byte-reversed value.*/
269CPU_BE( rev tmp3, data1 )
270CPU_BE( sub tmp1, tmp3, zeroones )
271CPU_BE( orr tmp2, tmp3, #REP8_7f )
272CPU_BE( bic has_nul, tmp1, tmp2 )
273CPU_BE( rev has_nul, has_nul )
274CPU_BE( orr syndrome, diff, has_nul )
275 /*
276 * The MS-non-zero bit of the syndrome marks either the first bit
277 * that is different, or the top bit of the first zero byte.
278 * Shifting left now will bring the critical information into the
279 * top bits.
280 */
281 clz pos, syndrome
282 lsl data1, data1, pos
283 lsl data2, data2, pos
284 /*
285 * But we need to zero-extend (char is unsigned) the value and then
286 * perform a signed 32-bit subtraction.
287 */
288 lsr data1, data1, #56
289 sub result, data1, data2, lsr #56
290 ret
291
292.Lremain8:
293 /* Limit % 8 == 0 => all bytes significant. */
294 ands limit, limit, #7
295 b.eq .Lret0
296.Ltiny8proc:
297 ldrb data1w, [src1], #1
298 ldrb data2w, [src2], #1
299 subs limit, limit, #1
300
301 ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
302 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
303 b.eq .Ltiny8proc
304 sub result, data1, data2
305 ret
306
307.Lret0:
308 mov result, #0
309 ret
310ENDPROC(strncmp)