summaryrefslogtreecommitdiffstats
path: root/src/runtime/vlop_arm.s
blob: 9e19938565569dbf2f08df9aadbcfa7bf41b81de (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
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
// Inferno's libkern/vlop-arm.s
// https://bitbucket.org/inferno-os/inferno-os/src/master/libkern/vlop-arm.s
//
//         Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
//         Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com).  All rights reserved.
//         Portions Copyright 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#include "go_asm.h"
#include "go_tls.h"
#include "funcdata.h"
#include "textflag.h"

// func runtime·udiv(n, d uint32) (q, r uint32)
// compiler knowns the register usage of this function
// Reference:
// Sloss, Andrew et. al; ARM System Developer's Guide: Designing and Optimizing System Software
// Morgan Kaufmann; 1 edition (April 8, 2004), ISBN 978-1558608740
#define Rq	R0 // input d, output q
#define Rr	R1 // input n, output r
#define Rs	R2 // three temporary variables
#define RM	R3
#define Ra	R11

// Be careful: Ra == R11 will be used by the linker for synthesized instructions.
// Note: this function does not have a frame.
TEXT runtime·udiv(SB),NOSPLIT|NOFRAME,$0
	MOVBU	internalcpu·ARM+const_offsetARMHasIDIVA(SB), Ra
	CMP	$0, Ra
	BNE	udiv_hardware

	CLZ 	Rq, Rs // find normalizing shift
	MOVW.S	Rq<<Rs, Ra
	MOVW	$fast_udiv_tab<>-64(SB), RM
	ADD.NE	Ra>>25, RM, Ra // index by most significant 7 bits of divisor
	MOVBU.NE	(Ra), Ra

	SUB.S	$7, Rs
	RSB 	$0, Rq, RM // M = -q
	MOVW.PL	Ra<<Rs, Rq

	// 1st Newton iteration
	MUL.PL	RM, Rq, Ra // a = -q*d
	BMI 	udiv_by_large_d
	MULAWT	Ra, Rq, Rq, Rq // q approx q-(q*q*d>>32)
	TEQ 	RM->1, RM // check for d=0 or d=1

	// 2nd Newton iteration
	MUL.NE	RM, Rq, Ra
	MOVW.NE	$0, Rs
	MULAL.NE Rq, Ra, (Rq,Rs)
	BEQ 	udiv_by_0_or_1

	// q now accurate enough for a remainder r, 0<=r<3*d
	MULLU	Rq, Rr, (Rq,Rs) // q = (r * q) >> 32
	ADD 	RM, Rr, Rr // r = n - d
	MULA	RM, Rq, Rr, Rr // r = n - (q+1)*d

	// since 0 <= n-q*d < 3*d; thus -d <= r < 2*d
	CMN 	RM, Rr // t = r-d
	SUB.CS	RM, Rr, Rr // if (t<-d || t>=0) r=r+d
	ADD.CC	$1, Rq
	ADD.PL	RM<<1, Rr
	ADD.PL	$2, Rq
	RET

// use hardware divider
udiv_hardware:
	DIVUHW	Rq, Rr, Rs
	MUL	Rs, Rq, RM
	RSB	Rr, RM, Rr
	MOVW	Rs, Rq
	RET

udiv_by_large_d:
	// at this point we know d>=2^(31-6)=2^25
	SUB 	$4, Ra, Ra
	RSB 	$0, Rs, Rs
	MOVW	Ra>>Rs, Rq
	MULLU	Rq, Rr, (Rq,Rs)
	MULA	RM, Rq, Rr, Rr

	// q now accurate enough for a remainder r, 0<=r<4*d
	CMN 	Rr>>1, RM // if(r/2 >= d)
	ADD.CS	RM<<1, Rr
	ADD.CS	$2, Rq
	CMN 	Rr, RM
	ADD.CS	RM, Rr
	ADD.CS	$1, Rq
	RET

udiv_by_0_or_1:
	// carry set if d==1, carry clear if d==0
	BCC udiv_by_0
	MOVW	Rr, Rq
	MOVW	$0, Rr
	RET

udiv_by_0:
	MOVW	$runtime·panicdivide(SB), R11
	B	(R11)

// var tab [64]byte
// tab[0] = 255; for i := 1; i <= 63; i++ { tab[i] = (1<<14)/(64+i) }
// laid out here as little-endian uint32s
DATA fast_udiv_tab<>+0x00(SB)/4, $0xf4f8fcff
DATA fast_udiv_tab<>+0x04(SB)/4, $0xe6eaedf0
DATA fast_udiv_tab<>+0x08(SB)/4, $0xdadde0e3
DATA fast_udiv_tab<>+0x0c(SB)/4, $0xcfd2d4d7
DATA fast_udiv_tab<>+0x10(SB)/4, $0xc5c7cacc
DATA fast_udiv_tab<>+0x14(SB)/4, $0xbcbec0c3
DATA fast_udiv_tab<>+0x18(SB)/4, $0xb4b6b8ba
DATA fast_udiv_tab<>+0x1c(SB)/4, $0xacaeb0b2
DATA fast_udiv_tab<>+0x20(SB)/4, $0xa5a7a8aa
DATA fast_udiv_tab<>+0x24(SB)/4, $0x9fa0a2a3
DATA fast_udiv_tab<>+0x28(SB)/4, $0x999a9c9d
DATA fast_udiv_tab<>+0x2c(SB)/4, $0x93949697
DATA fast_udiv_tab<>+0x30(SB)/4, $0x8e8f9092
DATA fast_udiv_tab<>+0x34(SB)/4, $0x898a8c8d
DATA fast_udiv_tab<>+0x38(SB)/4, $0x85868788
DATA fast_udiv_tab<>+0x3c(SB)/4, $0x81828384
GLOBL fast_udiv_tab<>(SB), RODATA, $64

// The linker will pass numerator in R8
#define Rn R8
// The linker expects the result in RTMP
#define RTMP R11

TEXT runtime·_divu(SB), NOSPLIT, $16-0
	// It's not strictly true that there are no local pointers.
	// It could be that the saved registers Rq, Rr, Rs, and Rm
	// contain pointers. However, the only way this can matter
	// is if the stack grows (which it can't, udiv is nosplit)
	// or if a fault happens and more frames are added to
	// the stack due to deferred functions.
	// In the latter case, the stack can grow arbitrarily,
	// and garbage collection can happen, and those
	// operations care about pointers, but in that case
	// the calling frame is dead, and so are the saved
	// registers. So we can claim there are no pointers here.
	NO_LOCAL_POINTERS
	MOVW	Rq, 4(R13)
	MOVW	Rr, 8(R13)
	MOVW	Rs, 12(R13)
	MOVW	RM, 16(R13)

	MOVW	Rn, Rr			/* numerator */
	MOVW	g_m(g), Rq
	MOVW	m_divmod(Rq), Rq	/* denominator */
	BL  	runtime·udiv(SB)
	MOVW	Rq, RTMP
	MOVW	4(R13), Rq
	MOVW	8(R13), Rr
	MOVW	12(R13), Rs
	MOVW	16(R13), RM
	RET

TEXT runtime·_modu(SB), NOSPLIT, $16-0
	NO_LOCAL_POINTERS
	MOVW	Rq, 4(R13)
	MOVW	Rr, 8(R13)
	MOVW	Rs, 12(R13)
	MOVW	RM, 16(R13)

	MOVW	Rn, Rr			/* numerator */
	MOVW	g_m(g), Rq
	MOVW	m_divmod(Rq), Rq	/* denominator */
	BL  	runtime·udiv(SB)
	MOVW	Rr, RTMP
	MOVW	4(R13), Rq
	MOVW	8(R13), Rr
	MOVW	12(R13), Rs
	MOVW	16(R13), RM
	RET

TEXT runtime·_div(SB),NOSPLIT,$16-0
	NO_LOCAL_POINTERS
	MOVW	Rq, 4(R13)
	MOVW	Rr, 8(R13)
	MOVW	Rs, 12(R13)
	MOVW	RM, 16(R13)
	MOVW	Rn, Rr			/* numerator */
	MOVW	g_m(g), Rq
	MOVW	m_divmod(Rq), Rq	/* denominator */
	CMP 	$0, Rr
	BGE 	d1
	RSB 	$0, Rr, Rr
	CMP 	$0, Rq
	BGE 	d2
	RSB 	$0, Rq, Rq
d0:
	BL  	runtime·udiv(SB)  	/* none/both neg */
	MOVW	Rq, RTMP
	B	out1
d1:
	CMP 	$0, Rq
	BGE 	d0
	RSB 	$0, Rq, Rq
d2:
	BL  	runtime·udiv(SB)  	/* one neg */
	RSB	$0, Rq, RTMP
out1:
	MOVW	4(R13), Rq
	MOVW	8(R13), Rr
	MOVW	12(R13), Rs
	MOVW	16(R13), RM
	RET

TEXT runtime·_mod(SB),NOSPLIT,$16-0
	NO_LOCAL_POINTERS
	MOVW	Rq, 4(R13)
	MOVW	Rr, 8(R13)
	MOVW	Rs, 12(R13)
	MOVW	RM, 16(R13)
	MOVW	Rn, Rr			/* numerator */
	MOVW	g_m(g), Rq
	MOVW	m_divmod(Rq), Rq	/* denominator */
	CMP 	$0, Rq
	RSB.LT	$0, Rq, Rq
	CMP 	$0, Rr
	BGE 	m1
	RSB 	$0, Rr, Rr
	BL  	runtime·udiv(SB)  	/* neg numerator */
	RSB 	$0, Rr, RTMP
	B   	out
m1:
	BL  	runtime·udiv(SB)  	/* pos numerator */
	MOVW	Rr, RTMP
out:
	MOVW	4(R13), Rq
	MOVW	8(R13), Rr
	MOVW	12(R13), Rs
	MOVW	16(R13), RM
	RET

// _mul64by32 and _div64by32 not implemented on arm
TEXT runtime·_mul64by32(SB), NOSPLIT, $0
	MOVW	$0, R0
	MOVW	(R0), R1 // crash

TEXT runtime·_div64by32(SB), NOSPLIT, $0
	MOVW	$0, R0
	MOVW	(R0), R1 // crash