Optimize LiteralAndZeroFillExpander.resetLiteral() [don't merge] #11
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drcrallen
suggested changes
Dec 9, 2016
| int trailingZeros = Integer.numberOfTrailingZeros(word); | ||
| offset += trailingZeros; | ||
| buffer[len++] = offset; | ||
| word >>>= trailingZeros; |
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Since we're shaving operations, you've already cleared the high bit here, do you really need unsigned shift?
leventov
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Added [don't merge] to title because it's not intended to be merged right now, because "the hardware is not ready". |
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drcrallen
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Feb 6, 2017
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@leventov does it SLOW down if that hardware intrinsic isn't present? |
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@drcrallen yes |
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This change makes concise bitset iteration from 1.5 to 3 times faster, but it requires
Integer.numberOfTrailingZeros()be a 1-tick intrinsic which is present on Intel Haswell+, while apparently we are running Druid historicals on AWS R3 instances, which are Ivy Bridge.