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runtime: add alignment info to sizeclasses.go comments
I was curious about the minimum possible alignment for each size class and the minimum size to guarantee any particular alignment (e.g., to know at what class size you can start assuming heap bits are byte- or word-aligned). Change-Id: I205b750286e8914986533c4f60712c420c3e63e9 Reviewed-on: https://go-review.googlesource.com/c/go/+/299909 Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> Trust: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Matthew Dempsky
parent
086357e8f6
commit
735647d92e
@ -37,6 +37,7 @@ import (
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"go/format"
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"io"
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"log"
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"math/bits"
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"os"
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)
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@ -242,8 +243,9 @@ nextk:
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}
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func printComment(w io.Writer, classes []class) {
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fmt.Fprintf(w, "// %-5s %-9s %-10s %-7s %-10s %-9s\n", "class", "bytes/obj", "bytes/span", "objects", "tail waste", "max waste")
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fmt.Fprintf(w, "// %-5s %-9s %-10s %-7s %-10s %-9s %-9s\n", "class", "bytes/obj", "bytes/span", "objects", "tail waste", "max waste", "min align")
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prevSize := 0
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var minAligns [32]int
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for i, c := range classes {
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if i == 0 {
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continue
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@ -252,8 +254,28 @@ func printComment(w io.Writer, classes []class) {
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objects := spanSize / c.size
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tailWaste := spanSize - c.size*(spanSize/c.size)
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maxWaste := float64((c.size-prevSize-1)*objects+tailWaste) / float64(spanSize)
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alignBits := bits.TrailingZeros(uint(c.size))
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for i := range minAligns {
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if i > alignBits {
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minAligns[i] = 0
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} else if minAligns[i] == 0 {
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minAligns[i] = c.size
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}
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}
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prevSize = c.size
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fmt.Fprintf(w, "// %5d %9d %10d %7d %10d %8.2f%%\n", i, c.size, spanSize, objects, tailWaste, 100*maxWaste)
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fmt.Fprintf(w, "// %5d %9d %10d %7d %10d %8.2f%% %9d\n", i, c.size, spanSize, objects, tailWaste, 100*maxWaste, 1<<alignBits)
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}
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fmt.Fprintf(w, "\n")
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fmt.Fprintf(w, "// %-9s %-4s %-12s\n", "alignment", "bits", "min obj size")
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for bits, size := range minAligns {
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if size == 0 {
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break
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}
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if bits+1 < len(minAligns) && size == minAligns[bits+1] {
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continue
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}
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fmt.Fprintf(w, "// %9d %4d %12d\n", 1<<bits, bits, size)
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}
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fmt.Fprintf(w, "\n")
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}
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@ -3,74 +3,83 @@
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package runtime
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// class bytes/obj bytes/span objects tail waste max waste
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// 1 8 8192 1024 0 87.50%
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// 2 16 8192 512 0 43.75%
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// 3 24 8192 341 8 29.24%
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// 4 32 8192 256 0 21.88%
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// 5 48 8192 170 32 31.52%
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// 6 64 8192 128 0 23.44%
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// 7 80 8192 102 32 19.07%
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// 8 96 8192 85 32 15.95%
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// 9 112 8192 73 16 13.56%
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// 10 128 8192 64 0 11.72%
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// 11 144 8192 56 128 11.82%
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// 12 160 8192 51 32 9.73%
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// 13 176 8192 46 96 9.59%
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// 14 192 8192 42 128 9.25%
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// 15 208 8192 39 80 8.12%
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// 16 224 8192 36 128 8.15%
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// 17 240 8192 34 32 6.62%
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// 18 256 8192 32 0 5.86%
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// 19 288 8192 28 128 12.16%
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// 20 320 8192 25 192 11.80%
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// 21 352 8192 23 96 9.88%
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// 22 384 8192 21 128 9.51%
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// 23 416 8192 19 288 10.71%
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// 24 448 8192 18 128 8.37%
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// 25 480 8192 17 32 6.82%
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// 26 512 8192 16 0 6.05%
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// 27 576 8192 14 128 12.33%
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// 28 640 8192 12 512 15.48%
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// 29 704 8192 11 448 13.93%
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// 30 768 8192 10 512 13.94%
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// 31 896 8192 9 128 15.52%
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// 32 1024 8192 8 0 12.40%
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// 33 1152 8192 7 128 12.41%
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// 34 1280 8192 6 512 15.55%
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// 35 1408 16384 11 896 14.00%
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// 36 1536 8192 5 512 14.00%
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// 37 1792 16384 9 256 15.57%
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// 38 2048 8192 4 0 12.45%
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// 39 2304 16384 7 256 12.46%
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// 40 2688 8192 3 128 15.59%
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// 41 3072 24576 8 0 12.47%
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// 42 3200 16384 5 384 6.22%
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// 43 3456 24576 7 384 8.83%
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// 44 4096 8192 2 0 15.60%
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// 45 4864 24576 5 256 16.65%
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// 46 5376 16384 3 256 10.92%
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// 47 6144 24576 4 0 12.48%
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// 48 6528 32768 5 128 6.23%
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// 49 6784 40960 6 256 4.36%
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// 50 6912 49152 7 768 3.37%
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// 51 8192 8192 1 0 15.61%
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// 52 9472 57344 6 512 14.28%
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// 53 9728 49152 5 512 3.64%
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// 54 10240 40960 4 0 4.99%
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// 55 10880 32768 3 128 6.24%
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// 56 12288 24576 2 0 11.45%
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// 57 13568 40960 3 256 9.99%
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// 58 14336 57344 4 0 5.35%
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// 59 16384 16384 1 0 12.49%
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// 60 18432 73728 4 0 11.11%
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// 61 19072 57344 3 128 3.57%
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// 62 20480 40960 2 0 6.87%
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// 63 21760 65536 3 256 6.25%
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// 64 24576 24576 1 0 11.45%
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// 65 27264 81920 3 128 10.00%
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// 66 28672 57344 2 0 4.91%
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// 67 32768 32768 1 0 12.50%
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// class bytes/obj bytes/span objects tail waste max waste min align
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// 1 8 8192 1024 0 87.50% 8
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// 2 16 8192 512 0 43.75% 16
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// 3 24 8192 341 8 29.24% 8
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// 4 32 8192 256 0 21.88% 32
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// 5 48 8192 170 32 31.52% 16
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// 6 64 8192 128 0 23.44% 64
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// 7 80 8192 102 32 19.07% 16
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// 8 96 8192 85 32 15.95% 32
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// 9 112 8192 73 16 13.56% 16
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// 10 128 8192 64 0 11.72% 128
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// 11 144 8192 56 128 11.82% 16
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// 12 160 8192 51 32 9.73% 32
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// 13 176 8192 46 96 9.59% 16
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// 14 192 8192 42 128 9.25% 64
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// 15 208 8192 39 80 8.12% 16
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// 16 224 8192 36 128 8.15% 32
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// 17 240 8192 34 32 6.62% 16
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// 18 256 8192 32 0 5.86% 256
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// 19 288 8192 28 128 12.16% 32
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// 20 320 8192 25 192 11.80% 64
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// 21 352 8192 23 96 9.88% 32
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// 22 384 8192 21 128 9.51% 128
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// 23 416 8192 19 288 10.71% 32
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// 24 448 8192 18 128 8.37% 64
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// 25 480 8192 17 32 6.82% 32
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// 26 512 8192 16 0 6.05% 512
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// 27 576 8192 14 128 12.33% 64
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// 28 640 8192 12 512 15.48% 128
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// 29 704 8192 11 448 13.93% 64
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// 30 768 8192 10 512 13.94% 256
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// 31 896 8192 9 128 15.52% 128
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// 32 1024 8192 8 0 12.40% 1024
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// 33 1152 8192 7 128 12.41% 128
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// 34 1280 8192 6 512 15.55% 256
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// 35 1408 16384 11 896 14.00% 128
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// 36 1536 8192 5 512 14.00% 512
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// 37 1792 16384 9 256 15.57% 256
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// 38 2048 8192 4 0 12.45% 2048
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// 39 2304 16384 7 256 12.46% 256
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// 40 2688 8192 3 128 15.59% 128
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// 41 3072 24576 8 0 12.47% 1024
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// 42 3200 16384 5 384 6.22% 128
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// 43 3456 24576 7 384 8.83% 128
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// 44 4096 8192 2 0 15.60% 4096
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// 45 4864 24576 5 256 16.65% 256
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// 46 5376 16384 3 256 10.92% 256
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// 47 6144 24576 4 0 12.48% 2048
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// 48 6528 32768 5 128 6.23% 128
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// 49 6784 40960 6 256 4.36% 128
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// 50 6912 49152 7 768 3.37% 256
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// 51 8192 8192 1 0 15.61% 8192
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// 52 9472 57344 6 512 14.28% 256
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// 53 9728 49152 5 512 3.64% 512
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// 54 10240 40960 4 0 4.99% 2048
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// 55 10880 32768 3 128 6.24% 128
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// 56 12288 24576 2 0 11.45% 4096
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// 57 13568 40960 3 256 9.99% 256
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// 58 14336 57344 4 0 5.35% 2048
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// 59 16384 16384 1 0 12.49% 16384
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// 60 18432 73728 4 0 11.11% 2048
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// 61 19072 57344 3 128 3.57% 128
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// 62 20480 40960 2 0 6.87% 4096
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// 63 21760 65536 3 256 6.25% 256
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// 64 24576 24576 1 0 11.45% 8192
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// 65 27264 81920 3 128 10.00% 128
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// 66 28672 57344 2 0 4.91% 4096
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// 67 32768 32768 1 0 12.50% 32768
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// alignment bits min obj size
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// 8 3 8
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// 16 4 32
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// 32 5 256
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// 64 6 512
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// 128 7 768
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// 4096 12 28672
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// 32768 15 32768
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const (
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_MaxSmallSize = 32768
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