diff options
author | Adriaan Moors <adriaan.moors@typesafe.com> | 2015-06-16 09:37:56 -0700 |
---|---|---|
committer | Adriaan Moors <adriaan.moors@typesafe.com> | 2015-06-16 09:37:56 -0700 |
commit | 43a56fb5a1b6450ce2bdf8f73ab30ca1b16d0778 (patch) | |
tree | 9492633b8954a2899e4a6fdd1bef4d412e30fd04 /src | |
parent | 6b09c66b8e982c84f8183a9c00e2d3a43455c2ac (diff) | |
parent | 9aae16aa231ad64e3987aaad2a206beaf10c76e0 (diff) | |
download | scala-43a56fb5a1b6450ce2bdf8f73ab30ca1b16d0778.tar.gz scala-43a56fb5a1b6450ce2bdf8f73ab30ca1b16d0778.tar.bz2 scala-43a56fb5a1b6450ce2bdf8f73ab30ca1b16d0778.zip |
Merge pull request #4534 from Ichoran/sorting-reimpl
Clean implementation of sorts for scala.util.Sorting.
Diffstat (limited to 'src')
-rw-r--r-- | src/library/scala/util/Sorting.scala | 712 |
1 files changed, 235 insertions, 477 deletions
diff --git a/src/library/scala/util/Sorting.scala b/src/library/scala/util/Sorting.scala index 2e021ad9d9..ee2bdbc4a7 100644 --- a/src/library/scala/util/Sorting.scala +++ b/src/library/scala/util/Sorting.scala @@ -1,6 +1,6 @@ /* __ *\ ** ________ ___ / / ___ Scala API ** -** / __/ __// _ | / / / _ | (c) 2006-2009, Ross Judson ** +** / __/ __// _ | / / / _ | (c) 2006-2015, LAMP/EPFL ** ** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ ** ** /____/\___/_/ |_/____/_/ | | ** ** |/ ** @@ -9,518 +9,276 @@ package scala package util -import scala.reflect.{ ClassTag, classTag } -import scala.math.{ Ordering, max, min } +import scala.reflect.ClassTag +import scala.math.Ordering -/** The Sorting object provides functions that can sort various kinds of - * objects. You can provide a comparison function, or you can request a sort - * of items that are viewable as [[scala.math.Ordered]]. Some sorts that - * operate directly on a subset of value types are also provided. These - * implementations are derived from those in the Sun JDK. +/** The `Sorting` object provides convenience wrappers for `java.util.Arrays.sort`. + * Methods that defer to `java.util.Arrays.sort` say that they do or under what + * conditions that they do. * - * Note that stability doesn't matter for value types, so use the `quickSort` - * variants for those. `stableSort` is intended to be used with - * objects when the prior ordering should be preserved, where possible. + * `Sorting` also implements a general-purpose quicksort and stable (merge) sort + * for those cases where `java.util.Arrays.sort` could only be used at the cost + * of a large memory penalty. If performance rather than memory usage is the + * primary concern, one may wish to find alternate strategies to use + * `java.util.Arrays.sort` directly e.g. by boxing primitives to use + * a custom ordering on them. + * + * `Sorting` provides methods where you can provide a comparison function, or + * can request a sort of items that are [[scala.math.Ordered]] or that + * otherwise have an implicit or explicit [[scala.math.Ordering]]. + * + * Note also that high-performance non-default sorts for numeric types + * are not provided. If this is required, it is advisable to investigate + * other libraries that cover this use case. * * @author Ross Judson - * @version 1.0 + * @author Adriaan Moors + * @author Rex Kerr + * @version 1.1 */ object Sorting { - /** Quickly sort an array of Doubles. */ - def quickSort(a: Array[Double]) { sort1(a, 0, a.length) } - - /** Quickly sort an array of items with an implicit Ordering. */ - def quickSort[K: Ordering](a: Array[K]) { sort1(a, 0, a.length) } - - /** Quickly sort an array of Ints. */ - def quickSort(a: Array[Int]) { sort1(a, 0, a.length) } - - /** Quickly sort an array of Floats. */ - def quickSort(a: Array[Float]) { sort1(a, 0, a.length) } - - /** Sort an array of K where K is Ordered, preserving the existing order - * where the values are equal. */ - def stableSort[K: ClassTag: Ordering](a: Array[K]) { - stableSort(a, 0, a.length-1, new Array[K](a.length), Ordering[K].lt _) - } + /** Sort an array of Doubles using `java.util.Arrays.sort`. */ + def quickSort(a: Array[Double]): Unit = java.util.Arrays.sort(a) - /** Sorts an array of `K` given an ordering function `f`. - * `f` should return `true` iff its first parameter is strictly less than its second parameter. - */ - def stableSort[K: ClassTag](a: Array[K], f: (K, K) => Boolean) { - stableSort(a, 0, a.length-1, new Array[K](a.length), f) - } + /** Sort an array of Ints using `java.util.Arrays.sort`. */ + def quickSort(a: Array[Int]): Unit = java.util.Arrays.sort(a) - /** Sorts an arbitrary sequence into an array, given a comparison function - * that should return `true` iff parameter one is strictly less than parameter two. - * - * @param a the sequence to be sorted. - * @param f the comparison function. - * @return the sorted sequence of items. - */ - def stableSort[K: ClassTag](a: Seq[K], f: (K, K) => Boolean): Array[K] = { - val ret = a.toArray - stableSort(ret, f) - ret - } + /** Sort an array of Floats using `java.util.Arrays.sort`. */ + def quickSort(a: Array[Float]): Unit = java.util.Arrays.sort(a) + + private final val qsortThreshold = 16 - /** Sorts an arbitrary sequence of items that are viewable as ordered. */ - def stableSort[K: ClassTag: Ordering](a: Seq[K]): Array[K] = - stableSort(a, Ordering[K].lt _) - - /** Stably sorts a sequence of items given an extraction function that will - * return an ordered key from an item. - * - * @param a the sequence to be sorted. - * @param f the comparison function. - * @return the sorted sequence of items. - */ - def stableSort[K: ClassTag, M: Ordering](a: Seq[K], f: K => M): Array[K] = - stableSort(a)(implicitly[ClassTag[K]], Ordering[M] on f) - - private def sort1[K: Ordering](x: Array[K], off: Int, len: Int) { - val ord = Ordering[K] - import ord._ - - def swap(a: Int, b: Int) { - val t = x(a) - x(a) = x(b) - x(b) = t - } - def vecswap(_a: Int, _b: Int, n: Int) { - var a = _a - var b = _b - var i = 0 - while (i < n) { - swap(a, b) - i += 1 - a += 1 - b += 1 - } - } - def med3(a: Int, b: Int, c: Int) = { - if (x(a) < x(b)) { - if (x(b) < x(c)) b else if (x(a) < x(c)) c else a - } else { - if (x(b) > x(c)) b else if (x(a) > x(c)) c else a - } - } - def sort2(off: Int, len: Int) { - // Insertion sort on smallest arrays - if (len < 7) { - var i = off - while (i < len + off) { - var j = i - while (j > off && x(j-1) > x(j)) { - swap(j, j-1) - j -= 1 + /** Sort array `a` with quicksort, using the Ordering on its elements. + * This algorithm sorts in place, so no additional memory is used aside from + * what might be required to box individual elements during comparison. + */ + def quickSort[K: Ordering](a: Array[K]): Unit = { + // Must have iN >= i0 or math will fail. Also, i0 >= 0. + def inner(a: Array[K], i0: Int, iN: Int, ord: Ordering[K]): Unit = { + if (iN - i0 < qsortThreshold) insertionSort(a, i0, iN, ord) + else { + var iK = (i0 + iN) >>> 1 // Unsigned div by 2 + // Find index of median of first, central, and last elements + var pL = + if (ord.compare(a(i0), a(iN - 1)) <= 0) + if (ord.compare(a(i0), a(iK)) < 0) + if (ord.compare(a(iN - 1), a(iK)) < 0) iN - 1 else iK + else i0 + else + if (ord.compare(a(i0), a(iK)) < 0) i0 + else + if (ord.compare(a(iN - 1), a(iK)) <= 0) iN - 1 + else iK + val pivot = a(pL) + // pL is the start of the pivot block; move it into the middle if needed + if (pL != iK) { a(pL) = a(iK); a(iK) = pivot; pL = iK } + // Elements equal to the pivot will be in range pL until pR + var pR = pL + 1 + // Items known to be less than pivot are below iA (range i0 until iA) + var iA = i0 + // Items known to be greater than pivot are at or above iB (range iB until iN) + var iB = iN + // Scan through everything in the buffer before the pivot(s) + while (pL - iA > 0) { + val current = a(iA) + ord.compare(current, pivot) match { + case 0 => + // Swap current out with pivot block + a(iA) = a(pL - 1) + a(pL - 1) = current + pL -= 1 + case x if x < 0 => + // Already in place. Just update indicies. + iA += 1 + case _ if iB > pR => + // Wrong side. There's room on the other side, so swap + a(iA) = a(iB - 1) + a(iB - 1) = current + iB -= 1 + case _ => + // Wrong side and there is no room. Swap by rotating pivot block. + a(iA) = a(pL - 1) + a(pL - 1) = a(pR - 1) + a(pR - 1) = current + pL -= 1 + pR -= 1 + iB -= 1 } - i += 1 } - } else { - // Choose a partition element, v - var m = off + (len >> 1) // Small arrays, middle element - if (len > 7) { - var l = off - var n = off + len - 1 - if (len > 40) { // Big arrays, pseudomedian of 9 - val s = len / 8 - l = med3(l, l+s, l+2*s) - m = med3(m-s, m, m+s) - n = med3(n-2*s, n-s, n) + // Get anything remaining in buffer after the pivot(s) + while (iB - pR > 0) { + val current = a(iB - 1) + ord.compare(current, pivot) match { + case 0 => + // Swap current out with pivot block + a(iB - 1) = a(pR) + a(pR) = current + pR += 1 + case x if x > 0 => + // Already in place. Just update indices. + iB -= 1 + case _ => + // Wrong side and we already know there is no room. Swap by rotating pivot block. + a(iB - 1) = a(pR) + a(pR) = a(pL) + a(pL) = current + iA += 1 + pL += 1 + pR += 1 } - m = med3(l, m, n) // Mid-size, med of 3 } - val v = x(m) - - // Establish Invariant: v* (<v)* (>v)* v* - var a = off - var b = a - var c = off + len - 1 - var d = c - var done = false - while (!done) { - while (b <= c && x(b) <= v) { - if (x(b) equiv v) { - swap(a, b) - a += 1 - } - b += 1 - } - while (c >= b && x(c) >= v) { - if (x(c) equiv v) { - swap(c, d) - d -= 1 - } - c -= 1 - } - if (b > c) { - done = true - } else { - swap(b, c) - c -= 1 - b += 1 - } + // Use tail recursion on large half (Sedgewick's method) so we don't blow up the stack if pivots are poorly chosen + if (iA - i0 < iN - iB) { + inner(a, i0, iA, ord) // True recursion + inner(a, iB, iN, ord) // Should be tail recursion + } + else { + inner(a, iB, iN, ord) // True recursion + inner(a, i0, iA, ord) // Should be tail recursion } - - // Swap partition elements back to middle - val n = off + len - var s = math.min(a-off, b-a) - vecswap(off, b-s, s) - s = math.min(d-c, n-d-1) - vecswap(b, n-s, s) - - // Recursively sort non-partition-elements - s = b - a - if (s > 1) - sort2(off, s) - s = d - c - if (s > 1) - sort2(n-s, s) } } - sort2(off, len) + inner(a, 0, a.length, implicitly[Ordering[K]]) } - - private def sort1(x: Array[Int], off: Int, len: Int) { - def swap(a: Int, b: Int) { - val t = x(a) - x(a) = x(b) - x(b) = t + + private final val mergeThreshold = 32 + + // Ordering[T] might be slow especially for boxed primitives, so use binary search variant of insertion sort + // Caller must pass iN >= i0 or math will fail. Also, i0 >= 0. + private def insertionSort[@specialized T](a: Array[T], i0: Int, iN: Int, ord: Ordering[T]): Unit = { + val n = iN - i0 + if (n < 2) return + if (ord.compare(a(i0), a(i0+1)) > 0) { + val temp = a(i0) + a(i0) = a(i0+1) + a(i0+1) = temp } - def vecswap(_a: Int, _b: Int, n: Int) { - var a = _a - var b = _b - var i = 0 - while (i < n) { - swap(a, b) - i += 1 - a += 1 - b += 1 - } - } - def med3(a: Int, b: Int, c: Int) = { - if (x(a) < x(b)) { - if (x(b) < x(c)) b else if (x(a) < x(c)) c else a - } else { - if (x(b) > x(c)) b else if (x(a) > x(c)) c else a - } - } - def sort2(off: Int, len: Int) { - // Insertion sort on smallest arrays - if (len < 7) { - var i = off - while (i < len + off) { - var j = i - while (j>off && x(j-1) > x(j)) { - swap(j, j-1) - j -= 1 - } - i += 1 + var m = 2 + while (m < n) { + // Speed up already-sorted case by checking last element first + val next = a(i0 + m) + if (ord.compare(next, a(i0+m-1)) < 0) { + var iA = i0 + var iB = i0 + m - 1 + while (iB - iA > 1) { + val ix = (iA + iB) >>> 1 // Use bit shift to get unsigned div by 2 + if (ord.compare(next, a(ix)) < 0) iB = ix + else iA = ix } - } else { - // Choose a partition element, v - var m = off + (len >> 1) // Small arrays, middle element - if (len > 7) { - var l = off - var n = off + len - 1 - if (len > 40) { // Big arrays, pseudomedian of 9 - val s = len / 8 - l = med3(l, l+s, l+2*s) - m = med3(m-s, m, m+s) - n = med3(n-2*s, n-s, n) - } - m = med3(l, m, n) // Mid-size, med of 3 - } - val v = x(m) - - // Establish Invariant: v* (<v)* (>v)* v* - var a = off - var b = a - var c = off + len - 1 - var d = c - var done = false - while (!done) { - while (b <= c && x(b) <= v) { - if (x(b) == v) { - swap(a, b) - a += 1 - } - b += 1 - } - while (c >= b && x(c) >= v) { - if (x(c) == v) { - swap(c, d) - d -= 1 - } - c -= 1 - } - if (b > c) { - done = true - } else { - swap(b, c) - c -= 1 - b += 1 - } + val ix = iA + (if (ord.compare(next, a(iA)) < 0) 0 else 1) + var i = i0 + m + while (i > ix) { + a(i) = a(i-1) + i -= 1 } - - // Swap partition elements back to middle - val n = off + len - var s = math.min(a-off, b-a) - vecswap(off, b-s, s) - s = math.min(d-c, n-d-1) - vecswap(b, n-s, s) - - // Recursively sort non-partition-elements - s = b - a - if (s > 1) - sort2(off, s) - s = d - c - if (s > 1) - sort2(n-s, s) + a(ix) = next } + m += 1 } - sort2(off, len) } - - private def sort1(x: Array[Double], off: Int, len: Int) { - def swap(a: Int, b: Int) { - val t = x(a) - x(a) = x(b) - x(b) = t + + // Caller is required to pass iN >= i0, else math will fail. Also, i0 >= 0. + private def mergeSort[@specialized T: ClassTag](a: Array[T], i0: Int, iN: Int, ord: Ordering[T], scratch: Array[T] = null): Unit = { + if (iN - i0 < mergeThreshold) insertionSort(a, i0, iN, ord) + else { + val iK = (i0 + iN) >>> 1 // Bit shift equivalent to unsigned math, no overflow + val sc = if (scratch eq null) new Array[T](iK - i0) else scratch + mergeSort(a, i0, iK, ord, sc) + mergeSort(a, iK, iN, ord, sc) + mergeSorted(a, i0, iK, iN, ord, sc) } - def vecswap(_a: Int, _b: Int, n: Int) { - var a = _a - var b = _b - var i = 0 - while (i < n) { - swap(a, b) + } + + // Must have 0 <= i0 < iK < iN + private def mergeSorted[@specialized T](a: Array[T], i0: Int, iK: Int, iN: Int, ord: Ordering[T], scratch: Array[T]): Unit = { + // Check to make sure we're not already in order + if (ord.compare(a(iK-1), a(iK)) > 0) { + var i = i0 + val jN = iK - i0 + var j = 0 + while (i < iK) { + scratch (j) = a(i) i += 1 - a += 1 - b += 1 - } - } - def med3(a: Int, b: Int, c: Int) = { - val ab = x(a) compare x(b) - val bc = x(b) compare x(c) - val ac = x(a) compare x(c) - if (ab < 0) { - if (bc < 0) b else if (ac < 0) c else a - } else { - if (bc > 0) b else if (ac > 0) c else a + j += 1 } - } - def sort2(off: Int, len: Int) { - // Insertion sort on smallest arrays - if (len < 7) { - var i = off - while (i < len + off) { - var j = i - while (j > off && (x(j-1) compare x(j)) > 0) { - swap(j, j-1) - j -= 1 - } - i += 1 - } - } else { - // Choose a partition element, v - var m = off + (len >> 1) // Small arrays, middle element - if (len > 7) { - var l = off - var n = off + len - 1 - if (len > 40) { // Big arrays, pseudomedian of 9 - val s = len / 8 - l = med3(l, l+s, l+2*s) - m = med3(m-s, m, m+s) - n = med3(n-2*s, n-s, n) - } - m = med3(l, m, n) // Mid-size, med of 3 - } - val v = x(m) - - // Establish Invariant: v* (<v)* (>v)* v* - var a = off - var b = a - var c = off + len - 1 - var d = c - var done = false - while (!done) { - var bv = x(b) compare v - while (b <= c && bv <= 0) { - if (bv == 0) { - swap(a, b) - a += 1 - } - b += 1 - if (b <= c) bv = x(b) compare v - } - var cv = x(c) compare v - while (c >= b && cv >= 0) { - if (cv == 0) { - swap(c, d) - d -= 1 - } - c -= 1 - if (c >= b) cv = x(c) compare v - } - if (b > c) { - done = true - } else { - swap(b, c) - c -= 1 - b += 1 - } - } - - // Swap partition elements back to middle - val n = off + len - var s = math.min(a-off, b-a) - vecswap(off, b-s, s) - s = math.min(d-c, n-d-1) - vecswap(b, n-s, s) - - // Recursively sort non-partition-elements - s = b - a - if (s > 1) - sort2(off, s) - s = d - c - if (s > 1) - sort2(n-s, s) + var k = i0 + j = 0 + while (i < iN && j < jN) { + if (ord.compare(a(i), scratch(j)) < 0) { a(k) = a(i); i += 1 } + else { a(k) = scratch(j); j += 1 } + k += 1 } + while (j < jN) { a(k) = scratch(j); j += 1; k += 1 } + // Don't need to finish a(i) because it's already in place, k = i } - sort2(off, len) } - - private def sort1(x: Array[Float], off: Int, len: Int) { - def swap(a: Int, b: Int) { - val t = x(a) - x(a) = x(b) - x(b) = t + + // Why would you even do this? + private def booleanSort(a: Array[Boolean]): Unit = { + var i = 0 + var n = 0 + while (i < a.length) { + if (!a(i)) n += 1 + i += 1 } - def vecswap(_a: Int, _b: Int, n: Int) { - var a = _a - var b = _b - var i = 0 - while (i < n) { - swap(a, b) - i += 1 - a += 1 - b += 1 - } + i = 0 + while (i < n) { + a(i) = false + i += 1 } - def med3(a: Int, b: Int, c: Int) = { - val ab = x(a) compare x(b) - val bc = x(b) compare x(c) - val ac = x(a) compare x(c) - if (ab < 0) { - if (bc < 0) b else if (ac < 0) c else a - } else { - if (bc > 0) b else if (ac > 0) c else a - } + while (i < a.length) { + a(i) = true + i += 1 } - def sort2(off: Int, len: Int) { - // Insertion sort on smallest arrays - if (len < 7) { - var i = off - while (i < len + off) { - var j = i - while (j > off && (x(j-1) compare x(j)) > 0) { - swap(j, j-1) - j -= 1 - } - i += 1 - } - } else { - // Choose a partition element, v - var m = off + (len >> 1) // Small arrays, middle element - if (len > 7) { - var l = off - var n = off + len - 1 - if (len > 40) { // Big arrays, pseudomedian of 9 - val s = len / 8 - l = med3(l, l+s, l+2*s) - m = med3(m-s, m, m+s) - n = med3(n-2*s, n-s, n) - } - m = med3(l, m, n) // Mid-size, med of 3 - } - val v = x(m) + } - // Establish Invariant: v* (<v)* (>v)* v* - var a = off - var b = a - var c = off + len - 1 - var d = c - var done = false - while (!done) { - var bv = x(b) compare v - while (b <= c && bv <= 0) { - if (bv == 0) { - swap(a, b) - a += 1 - } - b += 1 - if (b <= c) bv = x(b) compare v - } - var cv = x(c) compare v - while (c >= b && cv >= 0) { - if (cv == 0) { - swap(c, d) - d -= 1 - } - c -= 1 - if (c >= b) cv = x(c) compare v - } - if (b > c) { - done = true - } else { - swap(b, c) - c -= 1 - b += 1 - } - } + // TODO: add upper bound: T <: AnyRef, propagate to callers below (not binary compatible) + // Maybe also rename all these methods to `sort`. + @inline private def sort[T](a: Array[T], ord: Ordering[T]): Unit = a match { + case _: Array[AnyRef] => + // Note that runtime matches are covariant, so could actually be any Array[T] s.t. T is not primitive (even boxed value classes) + if (a.length > 1 && (ord eq null)) throw new NullPointerException("Ordering") + java.util.Arrays.sort(a, ord) + case a: Array[Int] => if (ord eq Ordering.Int) java.util.Arrays.sort(a) else mergeSort[Int](a, 0, a.length, ord) + case a: Array[Double] => mergeSort[Double](a, 0, a.length, ord) // Because not all NaNs are identical, stability is meaningful! + case a: Array[Long] => if (ord eq Ordering.Long) java.util.Arrays.sort(a) else mergeSort[Long](a, 0, a.length, ord) + case a: Array[Float] => mergeSort[Float](a, 0, a.length, ord) // Because not all NaNs are identical, stability is meaningful! + case a: Array[Char] => if (ord eq Ordering.Char) java.util.Arrays.sort(a) else mergeSort[Char](a, 0, a.length, ord) + case a: Array[Byte] => if (ord eq Ordering.Byte) java.util.Arrays.sort(a) else mergeSort[Byte](a, 0, a.length, ord) + case a: Array[Short] => if (ord eq Ordering.Short) java.util.Arrays.sort(a) else mergeSort[Short](a, 0, a.length, ord) + case a: Array[Boolean] => if (ord eq Ordering.Boolean) booleanSort(a) else mergeSort[Boolean](a, 0, a.length, ord) + // Array[Unit] is matched as an Array[AnyRef] due to covariance in runtime matching. Not worth catching it as a special case. + case null => throw new NullPointerException + } - // Swap partition elements back to middle - val n = off + len - var s = math.min(a-off, b-a) - vecswap(off, b-s, s) - s = math.min(d-c, n-d-1) - vecswap(b, n-s, s) + // TODO: remove unnecessary ClassTag (not binary compatible) + /** Sort array `a` using the Ordering on its elements, preserving the original ordering where possible. Uses `java.util.Arrays.sort` unless `K` is a primitive type. */ + def stableSort[K: ClassTag: Ordering](a: Array[K]): Unit = sort(a, Ordering[K]) - // Recursively sort non-partition-elements - s = b - a - if (s > 1) - sort2(off, s) - s = d - c - if (s > 1) - sort2(n-s, s) - } - } - sort2(off, len) + // TODO: Remove unnecessary ClassTag (not binary compatible) + // TODO: make this fast for primitive K (could be specialized if it didn't go through Ordering) + /** Sort array `a` using function `f` that computes the less-than relation for each element. Uses `java.util.Arrays.sort` unless `K` is a primitive type. */ + def stableSort[K: ClassTag](a: Array[K], f: (K, K) => Boolean): Unit = sort(a, Ordering fromLessThan f) + + /** A sorted Array, using the Ordering for the elements in the sequence `a`. Uses `java.util.Arrays.sort` unless `K` is a primitive type. */ + def stableSort[K: ClassTag: Ordering](a: Seq[K]): Array[K] = { + val ret = a.toArray + sort(ret, Ordering[K]) + ret } - private def stableSort[K : ClassTag](a: Array[K], lo: Int, hi: Int, scratch: Array[K], f: (K,K) => Boolean) { - if (lo < hi) { - val mid = (lo+hi) / 2 - stableSort(a, lo, mid, scratch, f) - stableSort(a, mid+1, hi, scratch, f) - var k, t_lo = lo - var t_hi = mid + 1 - while (k <= hi) { - if ((t_lo <= mid) && ((t_hi > hi) || (!f(a(t_hi), a(t_lo))))) { - scratch(k) = a(t_lo) - t_lo += 1 - } else { - scratch(k) = a(t_hi) - t_hi += 1 - } - k += 1 - } - k = lo - while (k <= hi) { - a(k) = scratch(k) - k += 1 - } - } + // TODO: make this fast for primitive K (could be specialized if it didn't go through Ordering) + /** A sorted Array, given a function `f` that computes the less-than relation for each item in the sequence `a`. Uses `java.util.Arrays.sort` unless `K` is a primitive type. */ + def stableSort[K: ClassTag](a: Seq[K], f: (K, K) => Boolean): Array[K] = { + val ret = a.toArray + sort(ret, Ordering fromLessThan f) + ret + } + + /** A sorted Array, given an extraction function `f` that returns an ordered key for each item in the sequence `a`. Uses `java.util.Arrays.sort` unless `K` is a primitive type. */ + def stableSort[K: ClassTag, M: Ordering](a: Seq[K], f: K => M): Array[K] = { + val ret = a.toArray + sort(ret, Ordering[M] on f) + ret } } |