xl: Rename getOrderedDisks as shuffleDisks appropriately. (#3796)

This PR is for readability cleanup

- getOrderedDisks as shuffleDisks
- getOrderedPartsMetadata as shufflePartsMetadata

Distribution is now a second argument instead being the
primary input argument for brevity.

Also change the usage of type casted int64(0), instead
rely on direct type reference as `var variable int64` everywhere.

cmd/xl-v1-utils.go

@@ -306,26 +306,34 @@ func readAllXLMetadata(disks []StorageAPI, bucket, object string) ([]xlMetaV1, [
 	return metadataArray, errs
 }
 
-// Return ordered partsMetadata depending on distribution.
-func getOrderedPartsMetadata(distribution []int, partsMetadata []xlMetaV1) (orderedPartsMetadata []xlMetaV1) {
-	orderedPartsMetadata = make([]xlMetaV1, len(partsMetadata))
+// Return shuffled partsMetadata depending on distribution.
+func shufflePartsMetadata(partsMetadata []xlMetaV1, distribution []int) (shuffledPartsMetadata []xlMetaV1) {
+	if distribution == nil {
+		return partsMetadata
+	}
+	shuffledPartsMetadata = make([]xlMetaV1, len(partsMetadata))
+	// Shuffle slice xl metadata for expected distribution.
 	for index := range partsMetadata {
 		blockIndex := distribution[index]
-		orderedPartsMetadata[blockIndex-1] = partsMetadata[index]
+		shuffledPartsMetadata[blockIndex-1] = partsMetadata[index]
 	}
-	return orderedPartsMetadata
+	return shuffledPartsMetadata
 }
 
-// getOrderedDisks - get ordered disks from erasure distribution.
-// returns ordered slice of disks from their actual distribution.
-func getOrderedDisks(distribution []int, disks []StorageAPI) (orderedDisks []StorageAPI) {
-	orderedDisks = make([]StorageAPI, len(disks))
-	// From disks gets ordered disks.
+// shuffleDisks - shuffle input disks slice depending on the
+// erasure distribution. return shuffled slice of disks with
+// their expected distribution.
+func shuffleDisks(disks []StorageAPI, distribution []int) (shuffledDisks []StorageAPI) {
+	if distribution == nil {
+		return disks
+	}
+	shuffledDisks = make([]StorageAPI, len(disks))
+	// Shuffle disks for expected distribution.
 	for index := range disks {
 		blockIndex := distribution[index]
-		orderedDisks[blockIndex-1] = disks[index]
+		shuffledDisks[blockIndex-1] = disks[index]
 	}
-	return orderedDisks
+	return shuffledDisks
 }
 
 // Errors specifically generated by getPartSizeFromIdx function.