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Issue #17118 Loop unrolling in Span.CopyTo slow path #18435

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ahsonkhan merged 2 commits into from
Apr 27, 2017
Merged

Issue #17118 Loop unrolling in Span.CopyTo slow path #18435

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Issue #17118 Loop unrolling in Span.CopyTo slow path
WinCPP Apr 18, 2017
6c5ccf9
Merge branch 'master' into Issue-17118-2
WinCPP Apr 26, 2017
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39 changes: 26 additions & 13 deletions src/System.Memory/src/System/SpanHelpers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -56,22 +56,35 @@ ref Unsafe.Add(ref srcBytes, (IntPtr)index),
? (uint)diff > (uint)-(int)dstByteCount
: (ulong)diff > (ulong)-(long)dstByteCount;

if (srcGreaterThanDst)
int direction = srcGreaterThanDst ? 1 : -1;
int runCount = srcGreaterThanDst ? 0 : srcLength - 1;

int loopCount = 0;
for (; loopCount < (srcLength & ~7); loopCount += 8)
{
// Source address greater than destination address. Can do normal copy.
for (int i = 0; i < srcLength; i++)
{
Unsafe.Add<T>(ref dst, i) = Unsafe.Add<T>(ref src, i);
}
Unsafe.Add<T>(ref dst, runCount + direction * 0) = Unsafe.Add<T>(ref src, runCount + direction * 0);
Unsafe.Add<T>(ref dst, runCount + direction * 1) = Unsafe.Add<T>(ref src, runCount + direction * 1);
Unsafe.Add<T>(ref dst, runCount + direction * 2) = Unsafe.Add<T>(ref src, runCount + direction * 2);
Unsafe.Add<T>(ref dst, runCount + direction * 3) = Unsafe.Add<T>(ref src, runCount + direction * 3);
Unsafe.Add<T>(ref dst, runCount + direction * 4) = Unsafe.Add<T>(ref src, runCount + direction * 4);
Unsafe.Add<T>(ref dst, runCount + direction * 5) = Unsafe.Add<T>(ref src, runCount + direction * 5);
Unsafe.Add<T>(ref dst, runCount + direction * 6) = Unsafe.Add<T>(ref src, runCount + direction * 6);
Unsafe.Add<T>(ref dst, runCount + direction * 7) = Unsafe.Add<T>(ref src, runCount + direction * 7);
runCount += direction * 8;
}
else
if (loopCount < (srcLength & ~3))
{
Unsafe.Add<T>(ref dst, runCount + direction * 0) = Unsafe.Add<T>(ref src, runCount + direction * 0);
Unsafe.Add<T>(ref dst, runCount + direction * 1) = Unsafe.Add<T>(ref src, runCount + direction * 1);
Unsafe.Add<T>(ref dst, runCount + direction * 2) = Unsafe.Add<T>(ref src, runCount + direction * 2);
Unsafe.Add<T>(ref dst, runCount + direction * 3) = Unsafe.Add<T>(ref src, runCount + direction * 3);
runCount += direction * 4;
loopCount += 4;
}
for (; loopCount < srcLength; ++loopCount)
{
// Source address less than or equal to destination address. Must do backward copy.
int i = srcLength;
while (i-- != 0)
{
Unsafe.Add<T>(ref dst, i) = Unsafe.Add<T>(ref src, i);
}
Unsafe.Add<T>(ref dst, runCount) = Unsafe.Add<T>(ref src, runCount);
runCount += direction;
}
}
}
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