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
|
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
using System.Runtime;
using Internal.Runtime.CompilerServices;
#if BIT64
using nuint = System.UInt64;
#else
using nuint = System.UInt32;
#endif
namespace System
{
internal static partial class SpanHelpers
{
public static unsafe void ClearWithoutReferences(ref byte b, nuint byteLength)
{
if (byteLength == 0)
return;
#if !PROJECTN && (AMD64 || ARM64)
// The exact matrix on when RhZeroMemory is faster than InitBlockUnaligned is very complex. The factors to consider include
// type of hardware and memory aligment. This threshold was chosen as a good balance accross different configurations.
if (byteLength > 768)
goto PInvoke;
Unsafe.InitBlockUnaligned(ref b, 0, (uint)byteLength);
return;
#else
// TODO: Optimize other platforms to be on par with AMD64 CoreCLR
// Note: It's important that this switch handles lengths at least up to 22.
// See notes below near the main loop for why.
// The switch will be very fast since it can be implemented using a jump
// table in assembly. See http://stackoverflow.com/a/449297/4077294 for more info.
switch (byteLength)
{
case 1:
b = 0;
return;
case 2:
Unsafe.As<byte, short>(ref b) = 0;
return;
case 3:
Unsafe.As<byte, short>(ref b) = 0;
Unsafe.Add<byte>(ref b, 2) = 0;
return;
case 4:
Unsafe.As<byte, int>(ref b) = 0;
return;
case 5:
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.Add<byte>(ref b, 4) = 0;
return;
case 6:
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
return;
case 7:
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.Add<byte>(ref b, 6) = 0;
return;
case 8:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
return;
case 9:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.Add<byte>(ref b, 8) = 0;
return;
case 10:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
return;
case 11:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.Add<byte>(ref b, 10) = 0;
return;
case 12:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
return;
case 13:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.Add<byte>(ref b, 12) = 0;
return;
case 14:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
return;
case 15:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
Unsafe.Add<byte>(ref b, 14) = 0;
return;
case 16:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
return;
case 17:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.Add<byte>(ref b, 16) = 0;
return;
case 18:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 16)) = 0;
return;
case 19:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 16)) = 0;
Unsafe.Add<byte>(ref b, 18) = 0;
return;
case 20:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 16)) = 0;
return;
case 21:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 16)) = 0;
Unsafe.Add<byte>(ref b, 20) = 0;
return;
case 22:
#if BIT64
Unsafe.As<byte, long>(ref b) = 0;
Unsafe.As<byte, long>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
#else
Unsafe.As<byte, int>(ref b) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 12)) = 0;
#endif
Unsafe.As<byte, int>(ref Unsafe.Add<byte>(ref b, 16)) = 0;
Unsafe.As<byte, short>(ref Unsafe.Add<byte>(ref b, 20)) = 0;
return;
}
// P/Invoke into the native version for large lengths
if (byteLength >= 512) goto PInvoke;
nuint i = 0; // byte offset at which we're copying
if (((nuint)Unsafe.AsPointer(ref b) & 3) != 0)
{
if (((nuint)Unsafe.AsPointer(ref b) & 1) != 0)
{
b = 0;
i += 1;
if (((nuint)Unsafe.AsPointer(ref b) & 2) != 0)
goto IntAligned;
}
Unsafe.As<byte, short>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
i += 2;
}
IntAligned:
// On 64-bit IntPtr.Size == 8, so we want to advance to the next 8-aligned address. If
// (int)b % 8 is 0, 5, 6, or 7, we will already have advanced by 0, 3, 2, or 1
// bytes to the next aligned address (respectively), so do nothing. On the other hand,
// if it is 1, 2, 3, or 4 we will want to copy-and-advance another 4 bytes until
// we're aligned.
// The thing 1, 2, 3, and 4 have in common that the others don't is that if you
// subtract one from them, their 3rd lsb will not be set. Hence, the below check.
if ((((nuint)Unsafe.AsPointer(ref b) - 1) & 4) == 0)
{
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
i += 4;
}
nuint end = byteLength - 16;
byteLength -= i; // lower 4 bits of byteLength represent how many bytes are left *after* the unrolled loop
// We know due to the above switch-case that this loop will always run 1 iteration; max
// bytes we clear before checking is 23 (7 to align the pointers, 16 for 1 iteration) so
// the switch handles lengths 0-22.
Debug.Assert(end >= 7 && i <= end);
// This is separated out into a different variable, so the i + 16 addition can be
// performed at the start of the pipeline and the loop condition does not have
// a dependency on the writes.
nuint counter;
do
{
counter = i + 16;
// This loop looks very costly since there appear to be a bunch of temporary values
// being created with the adds, but the jit (for x86 anyways) will convert each of
// these to use memory addressing operands.
// So the only cost is a bit of code size, which is made up for by the fact that
// we save on writes to b.
#if BIT64
Unsafe.As<byte, long>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
Unsafe.As<byte, long>(ref Unsafe.AddByteOffset<byte>(ref b, i + 8)) = 0;
#else
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i + 4)) = 0;
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i + 8)) = 0;
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i + 12)) = 0;
#endif
i = counter;
// See notes above for why this wasn't used instead
// i += 16;
}
while (counter <= end);
if ((byteLength & 8) != 0)
{
#if BIT64
Unsafe.As<byte, long>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
#else
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i + 4)) = 0;
#endif
i += 8;
}
if ((byteLength & 4) != 0)
{
Unsafe.As<byte, int>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
i += 4;
}
if ((byteLength & 2) != 0)
{
Unsafe.As<byte, short>(ref Unsafe.AddByteOffset<byte>(ref b, i)) = 0;
i += 2;
}
if ((byteLength & 1) != 0)
{
Unsafe.AddByteOffset<byte>(ref b, i) = 0;
// We're not using i after this, so not needed
// i += 1;
}
return;
#endif
PInvoke:
RuntimeImports.RhZeroMemory(ref b, byteLength);
}
public static unsafe void ClearWithReferences(ref IntPtr ip, nuint pointerSizeLength)
{
Debug.Assert((int)Unsafe.AsPointer(ref ip) % sizeof(IntPtr) == 0, "Should've been aligned on natural word boundary.");
// First write backward 8 natural words at a time.
// Writing backward allows us to get away with only simple modifications to the
// mov instruction's base and index registers between loop iterations.
for (; pointerSizeLength >= 8; pointerSizeLength -= 8)
{
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -1) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -2) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -3) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -4) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -5) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -6) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -7) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -8) = default;
}
Debug.Assert(pointerSizeLength <= 7);
// The logic below works by trying to minimize the number of branches taken for any
// given range of lengths. For example, the lengths [ 4 .. 7 ] are handled by a single
// branch, [ 2 .. 3 ] are handled by a single branch, and [ 1 ] is handled by a single
// branch.
//
// We can write both forward and backward as a perf improvement. For example,
// the lengths [ 4 .. 7 ] can be handled by zeroing out the first four natural
// words and the last 3 natural words. In the best case (length = 7), there are
// no overlapping writes. In the worst case (length = 4), there are three
// overlapping writes near the middle of the buffer. In perf testing, the
// penalty for performing duplicate writes is less expensive than the penalty
// for complex branching.
if (pointerSizeLength >= 4)
{
goto Write4To7;
}
else if (pointerSizeLength >= 2)
{
goto Write2To3;
}
else if (pointerSizeLength > 0)
{
goto Write1;
}
else
{
return; // nothing to write
}
Write4To7:
Debug.Assert(pointerSizeLength >= 4);
// Write first four and last three.
Unsafe.Add(ref ip, 2) = default;
Unsafe.Add(ref ip, 3) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -3) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -2) = default;
Write2To3:
Debug.Assert(pointerSizeLength >= 2);
// Write first two and last one.
Unsafe.Add(ref ip, 1) = default;
Unsafe.Add(ref Unsafe.Add(ref ip, (IntPtr)pointerSizeLength), -1) = default;
Write1:
Debug.Assert(pointerSizeLength >= 1);
// Write only element.
ip = default;
}
}
}
|
