From 6b5963335ea630eaa70d7b1ce1e89189dc92c60b Mon Sep 17 00:00:00 2001
From: Andy Balholm <andy@balholm.com>
Date: Thu, 7 May 2020 17:51:21 -0700
Subject: [PATCH] Use sort.Sort to sort Huffman trees.

---
 brotli_bit_stream.go | 11 ++++---
 entropy_encode.go    | 69 +++++++++-----------------------------------
 2 files changed, 19 insertions(+), 61 deletions(-)

diff --git a/brotli_bit_stream.go b/brotli_bit_stream.go
index 23d63f1..4e5d105 100644
--- a/brotli_bit_stream.go
+++ b/brotli_bit_stream.go
@@ -1,6 +1,9 @@
 package brotli
 
-import "math"
+import (
+	"math"
+	"sort"
+)
 
 const maxHuffmanTreeSize = (2*numCommandSymbols + 1)
 
@@ -411,10 +414,6 @@ func buildAndStoreHuffmanTree(histogram []uint32, histogram_length uint, alphabe
 	}
 }
 
-func sortHuffmanTree1(v0 huffmanTree, v1 huffmanTree) bool {
-	return v0.total_count_ < v1.total_count_
-}
-
 func buildAndStoreHuffmanTreeFast(histogram []uint32, histogram_total uint, max_bits uint, depth []byte, bits []uint16, storage_ix *uint, storage []byte) {
 	var count uint = 0
 	var symbols = [4]uint{0}
@@ -471,7 +470,7 @@ func buildAndStoreHuffmanTreeFast(histogram []uint32, histogram_total uint, max_
 				var j int = n + 1
 				var k int
 
-				sortHuffmanTreeItems(tree, uint(n), huffmanTreeComparator(sortHuffmanTree1))
+				sort.Sort(sortHuffmanTree(tree[:n]))
 
 				/* The nodes are:
 				   [0, n): the sorted leaf nodes that we start with.
diff --git a/entropy_encode.go b/entropy_encode.go
index 3f469a3..e48ca25 100644
--- a/entropy_encode.go
+++ b/entropy_encode.go
@@ -1,6 +1,9 @@
 package brotli
 
-import "math"
+import (
+	"math"
+	"sort"
+)
 
 /* Copyright 2010 Google Inc. All Rights Reserved.
 
@@ -23,55 +26,6 @@ func initHuffmanTree(self *huffmanTree, count uint32, left int16, right int16) {
 	self.index_right_or_value_ = right
 }
 
-/* Input size optimized Shell sort. */
-type huffmanTreeComparator func(huffmanTree, huffmanTree) bool
-
-var sortHuffmanTreeItems_gaps = []uint{132, 57, 23, 10, 4, 1}
-
-func sortHuffmanTreeItems(items []huffmanTree, n uint, comparator huffmanTreeComparator) {
-	if n < 13 {
-		/* Insertion sort. */
-		var i uint
-		for i = 1; i < n; i++ {
-			var tmp huffmanTree = items[i]
-			var k uint = i
-			var j uint = i - 1
-			for comparator(tmp, items[j]) {
-				items[k] = items[j]
-				k = j
-				if j == 0 {
-					break
-				}
-				j--
-			}
-
-			items[k] = tmp
-		}
-
-		return
-	} else {
-		var g int
-		if n < 57 {
-			g = 2
-		} else {
-			g = 0
-		}
-		for ; g < 6; g++ {
-			var gap uint = sortHuffmanTreeItems_gaps[g]
-			var i uint
-			for i = gap; i < n; i++ {
-				var j uint = i
-				var tmp huffmanTree = items[i]
-				for ; j >= gap && comparator(tmp, items[j-gap]); j -= gap {
-					items[j] = items[j-gap]
-				}
-
-				items[j] = tmp
-			}
-		}
-	}
-}
-
 /* Returns 1 if assignment of depths succeeded, otherwise 0. */
 func setDepth(p0 int, pool []huffmanTree, depth []byte, max_depth int) bool {
 	var stack [16]int
@@ -104,12 +58,17 @@ func setDepth(p0 int, pool []huffmanTree, depth []byte, max_depth int) bool {
 }
 
 /* Sort the root nodes, least popular first. */
-func sortHuffmanTree(v0 huffmanTree, v1 huffmanTree) bool {
-	if v0.total_count_ != v1.total_count_ {
-		return v0.total_count_ < v1.total_count_
+type sortHuffmanTree []huffmanTree
+
+func (s sortHuffmanTree) Len() int      { return len(s) }
+func (s sortHuffmanTree) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+func (s sortHuffmanTree) Less(i, j int) bool {
+	if s[i].total_count_ != s[j].total_count_ {
+		return s[i].total_count_ < s[j].total_count_
 	}
 
-	return v0.index_right_or_value_ > v1.index_right_or_value_
+	return s[i].index_right_or_value_ > s[j].index_right_or_value_
 }
 
 /* This function will create a Huffman tree.
@@ -155,7 +114,7 @@ func createHuffmanTree(data []uint32, length uint, tree_limit int, tree []huffma
 			break
 		}
 
-		sortHuffmanTreeItems(tree, n, huffmanTreeComparator(sortHuffmanTree))
+		sort.Sort(sortHuffmanTree(tree[:n]))
 
 		/* The nodes are:
 		   [0, n): the sorted leaf nodes that we start with.