Text file
src/runtime/vlop_arm.s
Documentation: runtime
1// Inferno's libkern/vlop-arm.s
2// https://bitbucket.org/inferno-os/inferno-os/src/master/libkern/vlop-arm.s
3//
4// Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
5// Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com). All rights reserved.
6// Portions Copyright 2009 The Go Authors. All rights reserved.
7//
8// Permission is hereby granted, free of charge, to any person obtaining a copy
9// of this software and associated documentation files (the "Software"), to deal
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13// furnished to do so, subject to the following conditions:
14//
15// The above copyright notice and this permission notice shall be included in
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17//
18// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
21// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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24// THE SOFTWARE.
25
26#include "go_asm.h"
27#include "go_tls.h"
28#include "funcdata.h"
29#include "textflag.h"
30
31// func runtime·udiv(n, d uint32) (q, r uint32)
32// compiler knowns the register usage of this function
33// Reference:
34// Sloss, Andrew et. al; ARM System Developer's Guide: Designing and Optimizing System Software
35// Morgan Kaufmann; 1 edition (April 8, 2004), ISBN 978-1558608740
36#define Rq R0 // input d, output q
37#define Rr R1 // input n, output r
38#define Rs R2 // three temporary variables
39#define RM R3
40#define Ra R11
41
42// Be careful: Ra == R11 will be used by the linker for synthesized instructions.
43// Note: this function does not have a frame.
44TEXT runtime·udiv(SB),NOSPLIT|NOFRAME,$0
45 MOVBU internal∕cpu·ARM+const_offsetARMHasIDIVA(SB), Ra
46 CMP $0, Ra
47 BNE udiv_hardware
48
49 CLZ Rq, Rs // find normalizing shift
50 MOVW.S Rq<<Rs, Ra
51 MOVW $fast_udiv_tab<>-64(SB), RM
52 ADD.NE Ra>>25, RM, Ra // index by most significant 7 bits of divisor
53 MOVBU.NE (Ra), Ra
54
55 SUB.S $7, Rs
56 RSB $0, Rq, RM // M = -q
57 MOVW.PL Ra<<Rs, Rq
58
59 // 1st Newton iteration
60 MUL.PL RM, Rq, Ra // a = -q*d
61 BMI udiv_by_large_d
62 MULAWT Ra, Rq, Rq, Rq // q approx q-(q*q*d>>32)
63 TEQ RM->1, RM // check for d=0 or d=1
64
65 // 2nd Newton iteration
66 MUL.NE RM, Rq, Ra
67 MOVW.NE $0, Rs
68 MULAL.NE Rq, Ra, (Rq,Rs)
69 BEQ udiv_by_0_or_1
70
71 // q now accurate enough for a remainder r, 0<=r<3*d
72 MULLU Rq, Rr, (Rq,Rs) // q = (r * q) >> 32
73 ADD RM, Rr, Rr // r = n - d
74 MULA RM, Rq, Rr, Rr // r = n - (q+1)*d
75
76 // since 0 <= n-q*d < 3*d; thus -d <= r < 2*d
77 CMN RM, Rr // t = r-d
78 SUB.CS RM, Rr, Rr // if (t<-d || t>=0) r=r+d
79 ADD.CC $1, Rq
80 ADD.PL RM<<1, Rr
81 ADD.PL $2, Rq
82 RET
83
84// use hardware divider
85udiv_hardware:
86 DIVUHW Rq, Rr, Rs
87 MUL Rs, Rq, RM
88 RSB Rr, RM, Rr
89 MOVW Rs, Rq
90 RET
91
92udiv_by_large_d:
93 // at this point we know d>=2^(31-6)=2^25
94 SUB $4, Ra, Ra
95 RSB $0, Rs, Rs
96 MOVW Ra>>Rs, Rq
97 MULLU Rq, Rr, (Rq,Rs)
98 MULA RM, Rq, Rr, Rr
99
100 // q now accurate enough for a remainder r, 0<=r<4*d
101 CMN Rr>>1, RM // if(r/2 >= d)
102 ADD.CS RM<<1, Rr
103 ADD.CS $2, Rq
104 CMN Rr, RM
105 ADD.CS RM, Rr
106 ADD.CS $1, Rq
107 RET
108
109udiv_by_0_or_1:
110 // carry set if d==1, carry clear if d==0
111 BCC udiv_by_0
112 MOVW Rr, Rq
113 MOVW $0, Rr
114 RET
115
116udiv_by_0:
117 MOVW $runtime·panicdivide(SB), R11
118 B (R11)
119
120// var tab [64]byte
121// tab[0] = 255; for i := 1; i <= 63; i++ { tab[i] = (1<<14)/(64+i) }
122// laid out here as little-endian uint32s
123DATA fast_udiv_tab<>+0x00(SB)/4, $0xf4f8fcff
124DATA fast_udiv_tab<>+0x04(SB)/4, $0xe6eaedf0
125DATA fast_udiv_tab<>+0x08(SB)/4, $0xdadde0e3
126DATA fast_udiv_tab<>+0x0c(SB)/4, $0xcfd2d4d7
127DATA fast_udiv_tab<>+0x10(SB)/4, $0xc5c7cacc
128DATA fast_udiv_tab<>+0x14(SB)/4, $0xbcbec0c3
129DATA fast_udiv_tab<>+0x18(SB)/4, $0xb4b6b8ba
130DATA fast_udiv_tab<>+0x1c(SB)/4, $0xacaeb0b2
131DATA fast_udiv_tab<>+0x20(SB)/4, $0xa5a7a8aa
132DATA fast_udiv_tab<>+0x24(SB)/4, $0x9fa0a2a3
133DATA fast_udiv_tab<>+0x28(SB)/4, $0x999a9c9d
134DATA fast_udiv_tab<>+0x2c(SB)/4, $0x93949697
135DATA fast_udiv_tab<>+0x30(SB)/4, $0x8e8f9092
136DATA fast_udiv_tab<>+0x34(SB)/4, $0x898a8c8d
137DATA fast_udiv_tab<>+0x38(SB)/4, $0x85868788
138DATA fast_udiv_tab<>+0x3c(SB)/4, $0x81828384
139GLOBL fast_udiv_tab<>(SB), RODATA, $64
140
141// The linker will pass numerator in R8
142#define Rn R8
143// The linker expects the result in RTMP
144#define RTMP R11
145
146TEXT runtime·_divu(SB), NOSPLIT, $16-0
147 // It's not strictly true that there are no local pointers.
148 // It could be that the saved registers Rq, Rr, Rs, and Rm
149 // contain pointers. However, the only way this can matter
150 // is if the stack grows (which it can't, udiv is nosplit)
151 // or if a fault happens and more frames are added to
152 // the stack due to deferred functions.
153 // In the latter case, the stack can grow arbitrarily,
154 // and garbage collection can happen, and those
155 // operations care about pointers, but in that case
156 // the calling frame is dead, and so are the saved
157 // registers. So we can claim there are no pointers here.
158 NO_LOCAL_POINTERS
159 MOVW Rq, 4(R13)
160 MOVW Rr, 8(R13)
161 MOVW Rs, 12(R13)
162 MOVW RM, 16(R13)
163
164 MOVW Rn, Rr /* numerator */
165 MOVW g_m(g), Rq
166 MOVW m_divmod(Rq), Rq /* denominator */
167 BL runtime·udiv(SB)
168 MOVW Rq, RTMP
169 MOVW 4(R13), Rq
170 MOVW 8(R13), Rr
171 MOVW 12(R13), Rs
172 MOVW 16(R13), RM
173 RET
174
175TEXT runtime·_modu(SB), NOSPLIT, $16-0
176 NO_LOCAL_POINTERS
177 MOVW Rq, 4(R13)
178 MOVW Rr, 8(R13)
179 MOVW Rs, 12(R13)
180 MOVW RM, 16(R13)
181
182 MOVW Rn, Rr /* numerator */
183 MOVW g_m(g), Rq
184 MOVW m_divmod(Rq), Rq /* denominator */
185 BL runtime·udiv(SB)
186 MOVW Rr, RTMP
187 MOVW 4(R13), Rq
188 MOVW 8(R13), Rr
189 MOVW 12(R13), Rs
190 MOVW 16(R13), RM
191 RET
192
193TEXT runtime·_div(SB),NOSPLIT,$16-0
194 NO_LOCAL_POINTERS
195 MOVW Rq, 4(R13)
196 MOVW Rr, 8(R13)
197 MOVW Rs, 12(R13)
198 MOVW RM, 16(R13)
199 MOVW Rn, Rr /* numerator */
200 MOVW g_m(g), Rq
201 MOVW m_divmod(Rq), Rq /* denominator */
202 CMP $0, Rr
203 BGE d1
204 RSB $0, Rr, Rr
205 CMP $0, Rq
206 BGE d2
207 RSB $0, Rq, Rq
208d0:
209 BL runtime·udiv(SB) /* none/both neg */
210 MOVW Rq, RTMP
211 B out1
212d1:
213 CMP $0, Rq
214 BGE d0
215 RSB $0, Rq, Rq
216d2:
217 BL runtime·udiv(SB) /* one neg */
218 RSB $0, Rq, RTMP
219out1:
220 MOVW 4(R13), Rq
221 MOVW 8(R13), Rr
222 MOVW 12(R13), Rs
223 MOVW 16(R13), RM
224 RET
225
226TEXT runtime·_mod(SB),NOSPLIT,$16-0
227 NO_LOCAL_POINTERS
228 MOVW Rq, 4(R13)
229 MOVW Rr, 8(R13)
230 MOVW Rs, 12(R13)
231 MOVW RM, 16(R13)
232 MOVW Rn, Rr /* numerator */
233 MOVW g_m(g), Rq
234 MOVW m_divmod(Rq), Rq /* denominator */
235 CMP $0, Rq
236 RSB.LT $0, Rq, Rq
237 CMP $0, Rr
238 BGE m1
239 RSB $0, Rr, Rr
240 BL runtime·udiv(SB) /* neg numerator */
241 RSB $0, Rr, RTMP
242 B out
243m1:
244 BL runtime·udiv(SB) /* pos numerator */
245 MOVW Rr, RTMP
246out:
247 MOVW 4(R13), Rq
248 MOVW 8(R13), Rr
249 MOVW 12(R13), Rs
250 MOVW 16(R13), RM
251 RET
252
253// _mul64by32 and _div64by32 not implemented on arm
254TEXT runtime·_mul64by32(SB), NOSPLIT, $0
255 MOVW $0, R0
256 MOVW (R0), R1 // crash
257
258TEXT runtime·_div64by32(SB), NOSPLIT, $0
259 MOVW $0, R0
260 MOVW (R0), R1 // crash
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