xref: /openbmc/linux/arch/arm64/lib/strncmp.S (revision 2359ccdd)
1/*
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
310ENDPIPROC(strncmp)
311