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author | Rex Kerr <ichoran@gmail.com> | 2015-05-30 11:35:25 -0700 |
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committer | Adriaan Moors <adriaan.moors@typesafe.com> | 2015-06-16 11:23:10 -0700 |
commit | 7d1b1292db82f33905f9a9ca214cf22f0a16591f (patch) | |
tree | d0545634e38b69c39050d9527ec5481539b02f83 /test/files/pos | |
parent | d4deb270b6ea9e6e75a535573470d173b55da9b2 (diff) | |
download | scala-7d1b1292db82f33905f9a9ca214cf22f0a16591f.tar.gz scala-7d1b1292db82f33905f9a9ca214cf22f0a16591f.tar.bz2 scala-7d1b1292db82f33905f9a9ca214cf22f0a16591f.zip |
Clean implementation of sorts for scala.util.Sorting.
Removed code based on Sun JDK sorts and implemented new (basic) sorts from
scratch. Deferred to Java Arrays.sort whenever practical. Behavior of
`scala.util.Sorting` should be unchanged, but changed documentation to
specify when the Java methods are being used (as they're typically very fast).
A JUnit test is provided.
Performance is important for sorts. Everything is better with this patch,
though it could be better yet, as described below.
Below are sort times (in microseconds, SEM < 5%) for various 1024-element
arrays of small case classes that compare on an int field (quickSort), or
int arrays that use custom ordering (stableSort). Note: "degenerate"
means there are only 16 values possible, so there are lots of ties.
Times are all with fresh data (no re-using cache from run to run).
Results:
```
random sorted reverse degenerate big:64k tiny:16
Old Sorting.quickSort 234 181 178 103 25,700 1.4
New Sorting.quickSort 170 27 115 74 18,600 0.8
Old Sorting.stableSort 321 234 236 282 32,600 2.1
New Sorting.stableSort 239 16 194 194 25,100 1.2
java.util.Arrays.sort 124 4 8 105 13,500 0.8
java.util.Arrays.sort|Box 126 15 13 112 13,200 0.9
```
The new versions are uniformly faster, but uniformly slower than Java sorting. scala.util.Sorting has use cases that don't map easily in to Java unless everything is pre-boxed, but the overhead of pre-boxing is minimal compared to the sort.
A snapshot of some of my benchmarking code is below.
(Yes, lots of repeating myself--it's dangerous not to when trying to get
somewhat accurate benchmarks.)
```
import java.util.Arrays
import java.util.Comparator
import math.Ordering
import util.Sorting
import reflect.ClassTag
val th = ichi.bench.Thyme.warmed()
case class N(i: Int, j: Int) {}
val a = Array.fill(1024)( Array.tabulate(1024)(i => N(util.Random.nextInt, i)) )
var ai = 0
val b = Array.fill(1024)( Array.tabulate(1024)(i => N(i, i)) )
var bi = 0
val c = Array.fill(1024)( Array.tabulate(1024)(i => N(1024-i, i)) )
var ci = 0
val d = Array.fill(1024)( Array.tabulate(1024)(i => N(util.Random.nextInt(16), i)) )
var di = 0
val e = Array.fill(16)( Array.tabulate(65536)(i => N(util.Random.nextInt, i)) )
var ei = 0
val f = Array.fill(65535)( Array.tabulate(16)(i => N(util.Random.nextInt, i)) )
var fi = 0
val o = new Ordering[N]{ def compare(a: N, b: N) = if (a.i < b.i) -1 else if (a.i > b.i) 1 else 0 }
for (s <- Seq("one", "two", "three")) {
println(s)
th.pbench{ val x = a(ai).clone; ai = (ai+1)%a.length; Sorting.quickSort(x)(o); x(x.length/3) }
th.pbench{ val x = b(bi).clone; bi = (bi+1)%b.length; Sorting.quickSort(x)(o); x(x.length/3) }
th.pbench{ val x = c(ci).clone; ci = (ci+1)%c.length; Sorting.quickSort(x)(o); x(x.length/3) }
th.pbench{ val x = d(di).clone; di = (di+1)%d.length; Sorting.quickSort(x)(o); x(x.length/3) }
th.pbench{ val x = e(ei).clone; ei = (ei+1)%e.length; Sorting.quickSort(x)(o); x(x.length/3) }
th.pbench{ val x = f(fi).clone; fi = (fi+1)%f.length; Sorting.quickSort(x)(o); x(x.length/3) }
}
def ix(ns: Array[N]) = {
val is = new Array[Int](ns.length)
var i = 0
while (i < ns.length) {
is(i) = ns(i).i
i += 1
}
is
}
val p = new Ordering[Int]{ def compare(a: Int, b: Int) = if (a > b) 1 else if (a < b) -1 else 0 }
for (s <- Seq("one", "two", "three")) {
println(s)
val tag: ClassTag[Int] = implicitly[ClassTag[Int]]
th.pbench{ val x = ix(a(ai)); ai = (ai+1)%a.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
th.pbench{ val x = ix(b(bi)); bi = (bi+1)%b.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
th.pbench{ val x = ix(c(ci)); ci = (ci+1)%c.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
th.pbench{ val x = ix(d(di)); di = (di+1)%d.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
th.pbench{ val x = ix(e(ei)); ei = (ei+1)%e.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
th.pbench{ val x = ix(f(fi)); fi = (fi+1)%f.length; Sorting.stableSort(x)(tag, p); x(x.length/3) }
}
for (s <- Seq("one", "two", "three")) {
println(s)
th.pbench{ val x = a(ai).clone; ai = (ai+1)%a.length; Arrays.sort(x, o); x(x.length/3) }
th.pbench{ val x = b(bi).clone; bi = (bi+1)%b.length; Arrays.sort(x, o); x(x.length/3) }
th.pbench{ val x = c(ci).clone; ci = (ci+1)%c.length; Arrays.sort(x, o); x(x.length/3) }
th.pbench{ val x = d(di).clone; di = (di+1)%d.length; Arrays.sort(x, o); x(x.length/3) }
th.pbench{ val x = e(ei).clone; ei = (ei+1)%e.length; Arrays.sort(x, o); x(x.length/3) }
th.pbench{ val x = f(fi).clone; fi = (fi+1)%f.length; Arrays.sort(x, o); x(x.length/3) }
}
def bx(is: Array[Int]): Array[java.lang.Integer] = {
val Is = new Array[java.lang.Integer](is.length)
var i = 0
while (i < is.length) {
Is(i) = java.lang.Integer.valueOf(is(i))
i += 1
}
Is
}
def xb(Is: Array[java.lang.Integer]): Array[Int] = {
val is = new Array[Int](Is.length)
var i = 0
while (i < is.length) {
is(i) = Is(i).intValue
i += 1
}
is
}
val q = new Comparator[java.lang.Integer]{
def compare(a: java.lang.Integer, b: java.lang.Integer) = o.compare(a.intValue, b.intValue)
}
for (s <- Seq("one", "two", "three")) {
println(s)
val tag: ClassTag[Int] = implicitly[ClassTag[Int]]
th.pbench{ val x = bx(ix(a(ai))); ai = (ai+1)%a.length; Arrays.sort(x, q); xb(x)(x.length/3) }
th.pbench{ val x = bx(ix(b(bi))); bi = (bi+1)%b.length; Arrays.sort(x, q); xb(x)(x.length/3) }
th.pbench{ val x = bx(ix(c(ci))); ci = (ci+1)%c.length; Arrays.sort(x, q); xb(x)(x.length/3) }
th.pbench{ val x = bx(ix(d(di))); di = (di+1)%d.length; Arrays.sort(x, q); xb(x)(x.length/3) }
th.pbench{ val x = bx(ix(e(ei))); ei = (ei+1)%e.length; Arrays.sort(x, q); xb(x)(x.length/3) }
th.pbench{ val x = bx(ix(f(fi))); fi = (fi+1)%f.length; Arrays.sort(x, q); xb(x)(x.length/3) }
}
```
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