summaryrefslogtreecommitdiffstats
path: root/src/math/big/arith_s390x.s
blob: aa6590e20a53da0d2829d72ca4edca3470f71700 (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
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build !math_big_pure_go
// +build !math_big_pure_go

#include "textflag.h"

// This file provides fast assembly versions for the elementary
// arithmetic operations on vectors implemented in arith.go.

// DI = R3, CX = R4, SI = r10, r8 = r8, r9=r9, r10 = r2, r11 = r5, r12 = r6, r13 = r7, r14 = r1 (R0 set to 0) + use R11
// func addVV(z, x, y []Word) (c Word)

TEXT ·addVV(SB), NOSPLIT, $0
	MOVD addvectorfacility+0x00(SB), R1
	BR   (R1)

TEXT ·addVV_check(SB), NOSPLIT, $0
	MOVB   ·hasVX(SB), R1
	CMPBEQ R1, $1, vectorimpl              // vectorfacility = 1, vector supported
	MOVD   $addvectorfacility+0x00(SB), R1
	MOVD   $·addVV_novec(SB), R2
	MOVD   R2, 0(R1)

	// MOVD	$·addVV_novec(SB), 0(R1)
	BR ·addVV_novec(SB)

vectorimpl:
	MOVD $addvectorfacility+0x00(SB), R1
	MOVD $·addVV_vec(SB), R2
	MOVD R2, 0(R1)

	// MOVD	$·addVV_vec(SB), 0(R1)
	BR ·addVV_vec(SB)

GLOBL addvectorfacility+0x00(SB), NOPTR, $8
DATA addvectorfacility+0x00(SB)/8, $·addVV_check(SB)

TEXT ·addVV_vec(SB), NOSPLIT, $0
	MOVD z_len+8(FP), R3
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD z+0(FP), R2

	MOVD $0, R4  // c = 0
	MOVD $0, R0  // make sure it's zero
	MOVD $0, R10 // i = 0

	// s/JL/JMP/ below to disable the unrolled loop
	SUB $4, R3
	BLT v1
	SUB $12, R3 // n -= 16
	BLT A1      // if n < 0 goto A1

	MOVD R8, R5
	MOVD R9, R6
	MOVD R2, R7

	// n >= 0
	// regular loop body unrolled 16x
	VZERO V0 // c = 0

UU1:
	VLM  0(R5), V1, V4    // 64-bytes into V1..V8
	ADD  $64, R5
	VPDI $0x4, V1, V1, V1 // flip the doublewords to big-endian order
	VPDI $0x4, V2, V2, V2 // flip the doublewords to big-endian order

	VLM  0(R6), V9, V12      // 64-bytes into V9..V16
	ADD  $64, R6
	VPDI $0x4, V9, V9, V9    // flip the doublewords to big-endian order
	VPDI $0x4, V10, V10, V10 // flip the doublewords to big-endian order

	VACCCQ V1, V9, V0, V25
	VACQ   V1, V9, V0, V17
	VACCCQ V2, V10, V25, V26
	VACQ   V2, V10, V25, V18

	VLM 0(R5), V5, V6   // 32-bytes into V1..V8
	VLM 0(R6), V13, V14 // 32-bytes into V9..V16
	ADD $32, R5
	ADD $32, R6

	VPDI $0x4, V3, V3, V3    // flip the doublewords to big-endian order
	VPDI $0x4, V4, V4, V4    // flip the doublewords to big-endian order
	VPDI $0x4, V11, V11, V11 // flip the doublewords to big-endian order
	VPDI $0x4, V12, V12, V12 // flip the doublewords to big-endian order

	VACCCQ V3, V11, V26, V27
	VACQ   V3, V11, V26, V19
	VACCCQ V4, V12, V27, V28
	VACQ   V4, V12, V27, V20

	VLM 0(R5), V7, V8   // 32-bytes into V1..V8
	VLM 0(R6), V15, V16 // 32-bytes into V9..V16
	ADD $32, R5
	ADD $32, R6

	VPDI $0x4, V5, V5, V5    // flip the doublewords to big-endian order
	VPDI $0x4, V6, V6, V6    // flip the doublewords to big-endian order
	VPDI $0x4, V13, V13, V13 // flip the doublewords to big-endian order
	VPDI $0x4, V14, V14, V14 // flip the doublewords to big-endian order

	VACCCQ V5, V13, V28, V29
	VACQ   V5, V13, V28, V21
	VACCCQ V6, V14, V29, V30
	VACQ   V6, V14, V29, V22

	VPDI $0x4, V7, V7, V7    // flip the doublewords to big-endian order
	VPDI $0x4, V8, V8, V8    // flip the doublewords to big-endian order
	VPDI $0x4, V15, V15, V15 // flip the doublewords to big-endian order
	VPDI $0x4, V16, V16, V16 // flip the doublewords to big-endian order

	VACCCQ V7, V15, V30, V31
	VACQ   V7, V15, V30, V23
	VACCCQ V8, V16, V31, V0  // V0 has carry-over
	VACQ   V8, V16, V31, V24

	VPDI  $0x4, V17, V17, V17 // flip the doublewords to big-endian order
	VPDI  $0x4, V18, V18, V18 // flip the doublewords to big-endian order
	VPDI  $0x4, V19, V19, V19 // flip the doublewords to big-endian order
	VPDI  $0x4, V20, V20, V20 // flip the doublewords to big-endian order
	VPDI  $0x4, V21, V21, V21 // flip the doublewords to big-endian order
	VPDI  $0x4, V22, V22, V22 // flip the doublewords to big-endian order
	VPDI  $0x4, V23, V23, V23 // flip the doublewords to big-endian order
	VPDI  $0x4, V24, V24, V24 // flip the doublewords to big-endian order
	VSTM  V17, V24, 0(R7)     // 128-bytes into z
	ADD   $128, R7
	ADD   $128, R10           // i += 16
	SUB   $16, R3             // n -= 16
	BGE   UU1                 // if n >= 0 goto U1
	VLGVG $1, V0, R4          // put cf into R4
	NEG   R4, R4              // save cf

A1:
	ADD $12, R3 // n += 16

	// s/JL/JMP/ below to disable the unrolled loop
	BLT v1 // if n < 0 goto v1

U1:  // n >= 0
	// regular loop body unrolled 4x
	MOVD 0(R8)(R10*1), R5
	MOVD 8(R8)(R10*1), R6
	MOVD 16(R8)(R10*1), R7
	MOVD 24(R8)(R10*1), R1
	ADDC R4, R4             // restore CF
	MOVD 0(R9)(R10*1), R11
	ADDE R11, R5
	MOVD 8(R9)(R10*1), R11
	ADDE R11, R6
	MOVD 16(R9)(R10*1), R11
	ADDE R11, R7
	MOVD 24(R9)(R10*1), R11
	ADDE R11, R1
	MOVD R0, R4
	ADDE R4, R4             // save CF
	NEG  R4, R4
	MOVD R5, 0(R2)(R10*1)
	MOVD R6, 8(R2)(R10*1)
	MOVD R7, 16(R2)(R10*1)
	MOVD R1, 24(R2)(R10*1)

	ADD $32, R10 // i += 4
	SUB $4, R3   // n -= 4
	BGE U1       // if n >= 0 goto U1

v1:
	ADD $4, R3 // n += 4
	BLE E1     // if n <= 0 goto E1

L1:  // n > 0
	ADDC R4, R4            // restore CF
	MOVD 0(R8)(R10*1), R5
	MOVD 0(R9)(R10*1), R11
	ADDE R11, R5
	MOVD R5, 0(R2)(R10*1)
	MOVD R0, R4
	ADDE R4, R4            // save CF
	NEG  R4, R4

	ADD $8, R10 // i++
	SUB $1, R3  // n--
	BGT L1      // if n > 0 goto L1

E1:
	NEG  R4, R4
	MOVD R4, c+72(FP) // return c
	RET

TEXT ·addVV_novec(SB), NOSPLIT, $0
novec:
	MOVD z_len+8(FP), R3
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD z+0(FP), R2

	MOVD $0, R4  // c = 0
	MOVD $0, R0  // make sure it's zero
	MOVD $0, R10 // i = 0

	// s/JL/JMP/ below to disable the unrolled loop
	SUB $4, R3 // n -= 4
	BLT v1n    // if n < 0 goto v1n

U1n:  // n >= 0
	// regular loop body unrolled 4x
	MOVD 0(R8)(R10*1), R5
	MOVD 8(R8)(R10*1), R6
	MOVD 16(R8)(R10*1), R7
	MOVD 24(R8)(R10*1), R1
	ADDC R4, R4             // restore CF
	MOVD 0(R9)(R10*1), R11
	ADDE R11, R5
	MOVD 8(R9)(R10*1), R11
	ADDE R11, R6
	MOVD 16(R9)(R10*1), R11
	ADDE R11, R7
	MOVD 24(R9)(R10*1), R11
	ADDE R11, R1
	MOVD R0, R4
	ADDE R4, R4             // save CF
	NEG  R4, R4
	MOVD R5, 0(R2)(R10*1)
	MOVD R6, 8(R2)(R10*1)
	MOVD R7, 16(R2)(R10*1)
	MOVD R1, 24(R2)(R10*1)

	ADD $32, R10 // i += 4
	SUB $4, R3   // n -= 4
	BGE U1n      // if n >= 0 goto U1n

v1n:
	ADD $4, R3 // n += 4
	BLE E1n    // if n <= 0 goto E1n

L1n:  // n > 0
	ADDC R4, R4            // restore CF
	MOVD 0(R8)(R10*1), R5
	MOVD 0(R9)(R10*1), R11
	ADDE R11, R5
	MOVD R5, 0(R2)(R10*1)
	MOVD R0, R4
	ADDE R4, R4            // save CF
	NEG  R4, R4

	ADD $8, R10 // i++
	SUB $1, R3  // n--
	BGT L1n     // if n > 0 goto L1n

E1n:
	NEG  R4, R4
	MOVD R4, c+72(FP) // return c
	RET

TEXT ·subVV(SB), NOSPLIT, $0
	MOVD subvectorfacility+0x00(SB), R1
	BR   (R1)

TEXT ·subVV_check(SB), NOSPLIT, $0
	MOVB   ·hasVX(SB), R1
	CMPBEQ R1, $1, vectorimpl              // vectorfacility = 1, vector supported
	MOVD   $subvectorfacility+0x00(SB), R1
	MOVD   $·subVV_novec(SB), R2
	MOVD   R2, 0(R1)

	// MOVD	$·subVV_novec(SB), 0(R1)
	BR ·subVV_novec(SB)

vectorimpl:
	MOVD $subvectorfacility+0x00(SB), R1
	MOVD $·subVV_vec(SB), R2
	MOVD R2, 0(R1)

	// MOVD	$·subVV_vec(SB), 0(R1)
	BR ·subVV_vec(SB)

GLOBL subvectorfacility+0x00(SB), NOPTR, $8
DATA subvectorfacility+0x00(SB)/8, $·subVV_check(SB)

// DI = R3, CX = R4, SI = r10, r8 = r8, r9=r9, r10 = r2, r11 = r5, r12 = r6, r13 = r7, r14 = r1 (R0 set to 0) + use R11
// func subVV(z, x, y []Word) (c Word)
// (same as addVV except for SUBC/SUBE instead of ADDC/ADDE and label names)
TEXT ·subVV_vec(SB), NOSPLIT, $0
	MOVD z_len+8(FP), R3
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD z+0(FP), R2
	MOVD $0, R4          // c = 0
	MOVD $0, R0          // make sure it's zero
	MOVD $0, R10         // i = 0

	// s/JL/JMP/ below to disable the unrolled loop
	SUB $4, R3  // n -= 4
	BLT v1      // if n < 0 goto v1
	SUB $12, R3 // n -= 16
	BLT A1      // if n < 0 goto A1

	MOVD R8, R5
	MOVD R9, R6
	MOVD R2, R7

	// n >= 0
	// regular loop body unrolled 16x
	VZERO V0         // cf = 0
	MOVD  $1, R4     // for 390 subtraction cf starts as 1 (no borrow)
	VLVGG $1, R4, V0 // put carry into V0

UU1:
	VLM  0(R5), V1, V4    // 64-bytes into V1..V8
	ADD  $64, R5
	VPDI $0x4, V1, V1, V1 // flip the doublewords to big-endian order
	VPDI $0x4, V2, V2, V2 // flip the doublewords to big-endian order

	VLM  0(R6), V9, V12      // 64-bytes into V9..V16
	ADD  $64, R6
	VPDI $0x4, V9, V9, V9    // flip the doublewords to big-endian order
	VPDI $0x4, V10, V10, V10 // flip the doublewords to big-endian order

	VSBCBIQ V1, V9, V0, V25
	VSBIQ   V1, V9, V0, V17
	VSBCBIQ V2, V10, V25, V26
	VSBIQ   V2, V10, V25, V18

	VLM 0(R5), V5, V6   // 32-bytes into V1..V8
	VLM 0(R6), V13, V14 // 32-bytes into V9..V16
	ADD $32, R5
	ADD $32, R6

	VPDI $0x4, V3, V3, V3    // flip the doublewords to big-endian order
	VPDI $0x4, V4, V4, V4    // flip the doublewords to big-endian order
	VPDI $0x4, V11, V11, V11 // flip the doublewords to big-endian order
	VPDI $0x4, V12, V12, V12 // flip the doublewords to big-endian order

	VSBCBIQ V3, V11, V26, V27
	VSBIQ   V3, V11, V26, V19
	VSBCBIQ V4, V12, V27, V28
	VSBIQ   V4, V12, V27, V20

	VLM 0(R5), V7, V8   // 32-bytes into V1..V8
	VLM 0(R6), V15, V16 // 32-bytes into V9..V16
	ADD $32, R5
	ADD $32, R6

	VPDI $0x4, V5, V5, V5    // flip the doublewords to big-endian order
	VPDI $0x4, V6, V6, V6    // flip the doublewords to big-endian order
	VPDI $0x4, V13, V13, V13 // flip the doublewords to big-endian order
	VPDI $0x4, V14, V14, V14 // flip the doublewords to big-endian order

	VSBCBIQ V5, V13, V28, V29
	VSBIQ   V5, V13, V28, V21
	VSBCBIQ V6, V14, V29, V30
	VSBIQ   V6, V14, V29, V22

	VPDI $0x4, V7, V7, V7    // flip the doublewords to big-endian order
	VPDI $0x4, V8, V8, V8    // flip the doublewords to big-endian order
	VPDI $0x4, V15, V15, V15 // flip the doublewords to big-endian order
	VPDI $0x4, V16, V16, V16 // flip the doublewords to big-endian order

	VSBCBIQ V7, V15, V30, V31
	VSBIQ   V7, V15, V30, V23
	VSBCBIQ V8, V16, V31, V0  // V0 has carry-over
	VSBIQ   V8, V16, V31, V24

	VPDI  $0x4, V17, V17, V17 // flip the doublewords to big-endian order
	VPDI  $0x4, V18, V18, V18 // flip the doublewords to big-endian order
	VPDI  $0x4, V19, V19, V19 // flip the doublewords to big-endian order
	VPDI  $0x4, V20, V20, V20 // flip the doublewords to big-endian order
	VPDI  $0x4, V21, V21, V21 // flip the doublewords to big-endian order
	VPDI  $0x4, V22, V22, V22 // flip the doublewords to big-endian order
	VPDI  $0x4, V23, V23, V23 // flip the doublewords to big-endian order
	VPDI  $0x4, V24, V24, V24 // flip the doublewords to big-endian order
	VSTM  V17, V24, 0(R7)     // 128-bytes into z
	ADD   $128, R7
	ADD   $128, R10           // i += 16
	SUB   $16, R3             // n -= 16
	BGE   UU1                 // if n >= 0 goto U1
	VLGVG $1, V0, R4          // put cf into R4
	SUB   $1, R4              // save cf

A1:
	ADD $12, R3 // n += 16
	BLT v1      // if n < 0 goto v1

U1:  // n >= 0
	// regular loop body unrolled 4x
	MOVD 0(R8)(R10*1), R5
	MOVD 8(R8)(R10*1), R6
	MOVD 16(R8)(R10*1), R7
	MOVD 24(R8)(R10*1), R1
	MOVD R0, R11
	SUBC R4, R11            // restore CF
	MOVD 0(R9)(R10*1), R11
	SUBE R11, R5
	MOVD 8(R9)(R10*1), R11
	SUBE R11, R6
	MOVD 16(R9)(R10*1), R11
	SUBE R11, R7
	MOVD 24(R9)(R10*1), R11
	SUBE R11, R1
	MOVD R0, R4
	SUBE R4, R4             // save CF
	MOVD R5, 0(R2)(R10*1)
	MOVD R6, 8(R2)(R10*1)
	MOVD R7, 16(R2)(R10*1)
	MOVD R1, 24(R2)(R10*1)

	ADD $32, R10 // i += 4
	SUB $4, R3   // n -= 4
	BGE U1       // if n >= 0 goto U1n

v1:
	ADD $4, R3 // n += 4
	BLE E1     // if n <= 0 goto E1

L1:  // n > 0
	MOVD R0, R11
	SUBC R4, R11           // restore CF
	MOVD 0(R8)(R10*1), R5
	MOVD 0(R9)(R10*1), R11
	SUBE R11, R5
	MOVD R5, 0(R2)(R10*1)
	MOVD R0, R4
	SUBE R4, R4            // save CF

	ADD $8, R10 // i++
	SUB $1, R3  // n--
	BGT L1      // if n > 0 goto L1n

E1:
	NEG  R4, R4
	MOVD R4, c+72(FP) // return c
	RET

// DI = R3, CX = R4, SI = r10, r8 = r8, r9=r9, r10 = r2, r11 = r5, r12 = r6, r13 = r7, r14 = r1 (R0 set to 0) + use R11
// func subVV(z, x, y []Word) (c Word)
// (same as addVV except for SUBC/SUBE instead of ADDC/ADDE and label names)
TEXT ·subVV_novec(SB), NOSPLIT, $0
	MOVD z_len+8(FP), R3
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD z+0(FP), R2

	MOVD $0, R4  // c = 0
	MOVD $0, R0  // make sure it's zero
	MOVD $0, R10 // i = 0

	// s/JL/JMP/ below to disable the unrolled loop
	SUB $4, R3 // n -= 4
	BLT v1     // if n < 0 goto v1

U1:  // n >= 0
	// regular loop body unrolled 4x
	MOVD 0(R8)(R10*1), R5
	MOVD 8(R8)(R10*1), R6
	MOVD 16(R8)(R10*1), R7
	MOVD 24(R8)(R10*1), R1
	MOVD R0, R11
	SUBC R4, R11            // restore CF
	MOVD 0(R9)(R10*1), R11
	SUBE R11, R5
	MOVD 8(R9)(R10*1), R11
	SUBE R11, R6
	MOVD 16(R9)(R10*1), R11
	SUBE R11, R7
	MOVD 24(R9)(R10*1), R11
	SUBE R11, R1
	MOVD R0, R4
	SUBE R4, R4             // save CF
	MOVD R5, 0(R2)(R10*1)
	MOVD R6, 8(R2)(R10*1)
	MOVD R7, 16(R2)(R10*1)
	MOVD R1, 24(R2)(R10*1)

	ADD $32, R10 // i += 4
	SUB $4, R3   // n -= 4
	BGE U1       // if n >= 0 goto U1

v1:
	ADD $4, R3 // n += 4
	BLE E1     // if n <= 0 goto E1

L1:  // n > 0
	MOVD R0, R11
	SUBC R4, R11           // restore CF
	MOVD 0(R8)(R10*1), R5
	MOVD 0(R9)(R10*1), R11
	SUBE R11, R5
	MOVD R5, 0(R2)(R10*1)
	MOVD R0, R4
	SUBE R4, R4            // save CF

	ADD $8, R10 // i++
	SUB $1, R3  // n--
	BGT L1      // if n > 0 goto L1

E1:
	NEG  R4, R4
	MOVD R4, c+72(FP) // return c
	RET

TEXT ·addVW(SB), NOSPLIT, $0
	MOVD z_len+8(FP), R5 // length of z
	MOVD x+24(FP), R6
	MOVD y+48(FP), R7    // c = y
	MOVD z+0(FP), R8

	CMPBEQ R5, $0, returnC // if len(z) == 0, we can have an early return

	// Add the first two words, and determine which path (copy path or loop path) to take based on the carry flag.
	ADDC   0(R6), R7
	MOVD   R7, 0(R8)
	CMPBEQ R5, $1, returnResult // len(z) == 1
	MOVD   $0, R9
	ADDE   8(R6), R9
	MOVD   R9, 8(R8)
	CMPBEQ R5, $2, returnResult // len(z) == 2

	// Update the counters
	MOVD $16, R12    // i = 2
	MOVD $-2(R5), R5 // n = n - 2

loopOverEachWord:
	BRC  $12, copySetup // carry = 0, copy the rest
	MOVD $1, R9

	// Originally we used the carry flag generated in the previous iteration
	// (i.e: ADDE could be used here to do the addition).  However, since we
	// already know carry is 1 (otherwise we will go to copy section), we can use
	// ADDC here so the current iteration does not depend on the carry flag
	// generated in the previous iteration. This could be useful when branch prediction happens.
	ADDC 0(R6)(R12*1), R9
	MOVD R9, 0(R8)(R12*1) // z[i] = x[i] + c

	MOVD  $8(R12), R12         // i++
	BRCTG R5, loopOverEachWord // n--

// Return the current carry value
returnResult:
	MOVD $0, R0
	ADDE R0, R0
	MOVD R0, c+56(FP)
	RET

// Update position of x(R6) and z(R8) based on the current counter value and perform copying.
// With the assumption that x and z will not overlap with each other or x and z will
// point to same memory region, we can use a faster version of copy using only MVC here.
// In the following implementation, we have three copy loops, each copying a word, 4 words, and
// 32 words at a time.  Via benchmarking, this implementation is faster than calling runtime·memmove.
copySetup:
	ADD R12, R6
	ADD R12, R8

	CMPBGE R5, $4, mediumLoop

smallLoop:  // does a loop unrolling to copy word when n < 4
	CMPBEQ R5, $0, returnZero
	MVC    $8, 0(R6), 0(R8)
	CMPBEQ R5, $1, returnZero
	MVC    $8, 8(R6), 8(R8)
	CMPBEQ R5, $2, returnZero
	MVC    $8, 16(R6), 16(R8)

returnZero:
	MOVD $0, c+56(FP) // return 0 as carry
	RET

mediumLoop:
	CMPBLT R5, $4, smallLoop
	CMPBLT R5, $32, mediumLoopBody

largeLoop:  // Copying 256 bytes at a time.
	MVC    $256, 0(R6), 0(R8)
	MOVD   $256(R6), R6
	MOVD   $256(R8), R8
	MOVD   $-32(R5), R5
	CMPBGE R5, $32, largeLoop
	BR     mediumLoop

mediumLoopBody:  // Copying 32 bytes at a time
	MVC    $32, 0(R6), 0(R8)
	MOVD   $32(R6), R6
	MOVD   $32(R8), R8
	MOVD   $-4(R5), R5
	CMPBGE R5, $4, mediumLoopBody
	BR     smallLoop

returnC:
	MOVD R7, c+56(FP)
	RET

TEXT ·subVW(SB), NOSPLIT, $0
	MOVD z_len+8(FP), R5
	MOVD x+24(FP), R6
	MOVD y+48(FP), R7    // The borrow bit passed in
	MOVD z+0(FP), R8
	MOVD $0, R0          // R0 is a temporary variable used during computation. Ensure it has zero in it.

	CMPBEQ R5, $0, returnC // len(z) == 0, have an early return

	// Subtract the first two words, and determine which path (copy path or loop path) to take based on the borrow flag
	MOVD   0(R6), R9
	SUBC   R7, R9
	MOVD   R9, 0(R8)
	CMPBEQ R5, $1, returnResult
	MOVD   8(R6), R9
	SUBE   R0, R9
	MOVD   R9, 8(R8)
	CMPBEQ R5, $2, returnResult

	// Update the counters
	MOVD $16, R12    // i = 2
	MOVD $-2(R5), R5 // n = n - 2

loopOverEachWord:
	BRC  $3, copySetup    // no borrow, copy the rest
	MOVD 0(R6)(R12*1), R9

	// Originally we used the borrow flag generated in the previous iteration
	// (i.e: SUBE could be used here to do the subtraction). However, since we
	// already know borrow is 1 (otherwise we will go to copy section), we can
	// use SUBC here so the current iteration does not depend on the borrow flag
	// generated in the previous iteration. This could be useful when branch prediction happens.
	SUBC $1, R9
	MOVD R9, 0(R8)(R12*1) // z[i] = x[i] - 1

	MOVD  $8(R12), R12         // i++
	BRCTG R5, loopOverEachWord // n--

// return the current borrow value
returnResult:
	SUBE R0, R0
	NEG  R0, R0
	MOVD R0, c+56(FP)
	RET

// Update position of x(R6) and z(R8) based on the current counter value and perform copying.
// With the assumption that x and z will not overlap with each other or x and z will
// point to same memory region, we can use a faster version of copy using only MVC here.
// In the following implementation, we have three copy loops, each copying a word, 4 words, and
// 32 words at a time. Via benchmarking, this implementation is faster than calling runtime·memmove.
copySetup:
	ADD R12, R6
	ADD R12, R8

	CMPBGE R5, $4, mediumLoop

smallLoop:  // does a loop unrolling to copy word when n < 4
	CMPBEQ R5, $0, returnZero
	MVC    $8, 0(R6), 0(R8)
	CMPBEQ R5, $1, returnZero
	MVC    $8, 8(R6), 8(R8)
	CMPBEQ R5, $2, returnZero
	MVC    $8, 16(R6), 16(R8)

returnZero:
	MOVD $0, c+56(FP) // return 0 as borrow
	RET

mediumLoop:
	CMPBLT R5, $4, smallLoop
	CMPBLT R5, $32, mediumLoopBody

largeLoop:  // Copying 256 bytes at a time
	MVC    $256, 0(R6), 0(R8)
	MOVD   $256(R6), R6
	MOVD   $256(R8), R8
	MOVD   $-32(R5), R5
	CMPBGE R5, $32, largeLoop
	BR     mediumLoop

mediumLoopBody:  // Copying 32 bytes at a time
	MVC    $32, 0(R6), 0(R8)
	MOVD   $32(R6), R6
	MOVD   $32(R8), R8
	MOVD   $-4(R5), R5
	CMPBGE R5, $4, mediumLoopBody
	BR     smallLoop

returnC:
	MOVD R7, c+56(FP)
	RET

// func shlVU(z, x []Word, s uint) (c Word)
TEXT ·shlVU(SB), NOSPLIT, $0
	BR ·shlVU_g(SB)

// func shrVU(z, x []Word, s uint) (c Word)
TEXT ·shrVU(SB), NOSPLIT, $0
	BR ·shrVU_g(SB)

// CX = R4, r8 = r8, r9=r9, r10 = r2, r11 = r5, DX = r3, AX = r6, BX = R1, (R0 set to 0) + use R11 + use R7 for i
// func mulAddVWW(z, x []Word, y, r Word) (c Word)
TEXT ·mulAddVWW(SB), NOSPLIT, $0
	MOVD z+0(FP), R2
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD r+56(FP), R4    // c = r
	MOVD z_len+8(FP), R5
	MOVD $0, R1          // i = 0
	MOVD $0, R7          // i*8 = 0
	MOVD $0, R0          // make sure it's zero
	BR   E5

L5:
	MOVD   (R8)(R1*1), R6
	MULHDU R9, R6
	ADDC   R4, R11         // add to low order bits
	ADDE   R0, R6
	MOVD   R11, (R2)(R1*1)
	MOVD   R6, R4
	ADD    $8, R1          // i*8 + 8
	ADD    $1, R7          // i++

E5:
	CMPBLT R7, R5, L5 // i < n

	MOVD R4, c+64(FP)
	RET

// func addMulVVW(z, x []Word, y Word) (c Word)
// CX = R4, r8 = r8, r9=r9, r10 = r2, r11 = r5, AX = r11, DX = R6, r12=r12, BX = R1, (R0 set to 0) + use R11 + use R7 for i
TEXT ·addMulVVW(SB), NOSPLIT, $0
	MOVD z+0(FP), R2
	MOVD x+24(FP), R8
	MOVD y+48(FP), R9
	MOVD z_len+8(FP), R5

	MOVD $0, R1 // i*8 = 0
	MOVD $0, R7 // i = 0
	MOVD $0, R0 // make sure it's zero
	MOVD $0, R4 // c = 0

	MOVD   R5, R12
	AND    $-2, R12
	CMPBGE R5, $2, A6
	BR     E6

A6:
	MOVD   (R8)(R1*1), R6
	MULHDU R9, R6
	MOVD   (R2)(R1*1), R10
	ADDC   R10, R11        // add to low order bits
	ADDE   R0, R6
	ADDC   R4, R11
	ADDE   R0, R6
	MOVD   R6, R4
	MOVD   R11, (R2)(R1*1)

	MOVD   (8)(R8)(R1*1), R6
	MULHDU R9, R6
	MOVD   (8)(R2)(R1*1), R10
	ADDC   R10, R11           // add to low order bits
	ADDE   R0, R6
	ADDC   R4, R11
	ADDE   R0, R6
	MOVD   R6, R4
	MOVD   R11, (8)(R2)(R1*1)

	ADD $16, R1 // i*8 + 8
	ADD $2, R7  // i++

	CMPBLT R7, R12, A6
	BR     E6

L6:
	MOVD   (R8)(R1*1), R6
	MULHDU R9, R6
	MOVD   (R2)(R1*1), R10
	ADDC   R10, R11        // add to low order bits
	ADDE   R0, R6
	ADDC   R4, R11
	ADDE   R0, R6
	MOVD   R6, R4
	MOVD   R11, (R2)(R1*1)

	ADD $8, R1 // i*8 + 8
	ADD $1, R7 // i++

E6:
	CMPBLT R7, R5, L6 // i < n

	MOVD R4, c+56(FP)
	RET