compress/bzip2: simplify Huffman tree construction

This change simplifies the construction of the Huffman tree in the
bzip2 package by replacing custom sort logic with the more concise and
idiomatic use of "slices" and "cmp" packages.

Change-Id: I2a8aef146b54b9433038b133d2cc8856ba077c72
GitHub-Last-Rev: c031bb5
GitHub-Pull-Request: #66817
Reviewed-on: https://go-review.googlesource.com/c/go/+/578438
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: aimuz

src/compress/bzip2/huffman.go

@@ -4,7 +4,10 @@
 
 package bzip2
 
-import "sort"
+import (
+	"cmp"
+	"slices"
+)
 
 // A huffmanTree is a binary tree which is navigated, bit-by-bit to reach a
 // symbol.
@@ -100,17 +103,11 @@ func newHuffmanTree(lengths []uint8) (huffmanTree, error) {
 		pairs[i].length = length
 	}
 
-	sort.Slice(pairs, func(i, j int) bool {
-		if pairs[i].length < pairs[j].length {
-			return true
+	slices.SortFunc(pairs, func(a, b huffmanSymbolLengthPair) int {
+		if c := cmp.Compare(a.length, b.length); c != 0 {
+			return c
 		}
-		if pairs[i].length > pairs[j].length {
-			return false
-		}
-		if pairs[i].value < pairs[j].value {
-			return true
-		}
-		return false
+		return cmp.Compare(a.value, b.value)
 	})
 
 	// Now we assign codes to the symbols, starting with the longest code.
@@ -135,8 +132,8 @@ func newHuffmanTree(lengths []uint8) (huffmanTree, error) {
 
 	// Now we can sort by the code so that the left half of each branch are
 	// grouped together, recursively.
-	sort.Slice(codes, func(i, j int) bool {
-		return codes[i].code < codes[j].code
+	slices.SortFunc(codes, func(a, b huffmanCode) int {
+		return cmp.Compare(a.code, b.code)
 	})
 
 	t.nodes = make([]huffmanNode, len(codes))