[#8] hrw: Do not create index slice for sorter

`ind` is only needed to index dist or weights, swap them directly.

```
goos: linux
goarch: amd64
pkg: git.frostfs.info/TrueCloudLab/hrw
cpu: 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz
                                              │      0      │                  1                   │
                                              │   sec/op    │    sec/op     vs base                │
SortHashersByValue_Typed_fnv_10-8               596.2n ± 4%   580.1n ±  1%   -2.72% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_100-8              4.453µ ± 2%   4.215µ ±  2%   -5.35% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_1000-8             41.58µ ± 4%   39.40µ ±  1%   -5.23% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_10-8          624.5n ± 2%   599.6n ±  2%   -3.99% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_100-8         4.593µ ± 2%   4.337µ ±  5%   -5.56% (p=0.003 n=10)
SortHashersByWeightValueTyped_fnv_1000-8        4.896µ ± 8%   4.344µ ±  3%  -11.27% (p=0.000 n=10)
geomean                                         4.668µ        4.400µ         -5.75%

                                              │      0       │                  1                   │
                                              │     B/op     │     B/op      vs base                │
SortHashersByValue_Typed_fnv_10-8                 584.0 ± 0%     472.0 ± 0%  -19.18% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_100-8              4.367Ki ± 0%   3.461Ki ± 0%  -20.75% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_1000-8             39.80Ki ± 0%   31.77Ki ± 0%  -20.18% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_10-8            600.0 ± 0%     472.0 ± 0%  -21.33% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_100-8         4.383Ki ± 0%   3.461Ki ± 0%  -21.03% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_1000-8        4.383Ki ± 0%   3.461Ki ± 0%  -21.03% (p=0.000 n=10)
geomean                                         3.742Ki        3.070Ki       -17.96%

                                              │      0      │                 1                  │
                                              │  allocs/op  │  allocs/op   vs base               │
SortHashersByValue_Typed_fnv_10-8                17.00 ± 0%    16.00 ± 0%  -5.88% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_100-8               107.0 ± 0%    106.0 ± 0%  -0.93% (p=0.000 n=10)
SortHashersByValue_Typed_fnv_1000-8             1.007k ± 0%   1.006k ± 0%  -0.10% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_10-8           17.00 ± 0%    16.00 ± 0%  -5.88% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_100-8          107.0 ± 0%    106.0 ± 0%  -0.93% (p=0.000 n=10)
SortHashersByWeightValueTyped_fnv_1000-8         107.0 ± 0%    106.0 ± 0%  -0.93% (p=0.000 n=10)
geomean                                          115.3         113.0       -1.94%
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

hrw.go

@@ -243,24 +243,6 @@ func ValidateWeights(weights []float64) error {
 	return nil
 }
 
-func newSorter(l int, byIndex bool, nodes []uint64, h uint64,
-	swap func(i, j int)) (*sorter, []int, []uint64) {
-	ind := make([]int, l)
-	dist := make([]uint64, l)
-	for i := 0; i < l; i++ {
-		ind[i] = i
-		dist[i] = getDistance(byIndex, i, nodes, h)
-	}
-
-	return &sorter{
-		l: l,
-		swap: func(i, j int) {
-			swap(i, j)
-			ind[i], ind[j] = ind[j], ind[i]
-		},
-	}, ind, dist
-}
-
 // sortByWeight sorts nodes by weight using provided swapper.
 // nodes contains hrw hashes. If it is nil, indices are used.
 func sortByWeight(l int, byIndex bool, nodes []uint64, weights []float64, hash uint64, swap func(i, j int)) {
@@ -270,14 +252,23 @@ func sortByWeight(l int, byIndex bool, nodes []uint64, weights []float64, hash u
 		return
 	}
 
-	s, ind, dist := newSorter(l, byIndex, nodes, hash, swap)
+	dist := make([]float64, l)
-	s.less = func(i, j int) bool {
+	for i := 0; i < l; i++ {
-		ii, jj := ind[i], ind[j]
+		d := getDistance(byIndex, i, nodes, hash)
 		// `maxUint64 - distance` makes the shorter distance more valuable
 		// it is necessary for operation with normalized values
-		wi := float64(^uint64(0)-dist[ii]) * weights[ii]
+		dist[i] = float64(^uint64(0)-d) * weights[i]
-		wj := float64(^uint64(0)-dist[jj]) * weights[jj]
+	}
-		return wi > wj // higher distance must be placed lower to be first
+
+	s := &sorter{
+		l: l,
+		swap: func(i, j int) {
+			swap(i, j)
+			dist[i], dist[j] = dist[j], dist[i]
+		},
+		less: func(i, j int) bool {
+			return dist[i] > dist[j] // higher distance must be placed lower to be first
+		},
 	}
 	sort.Sort(s)
 }
@@ -285,9 +276,20 @@ func sortByWeight(l int, byIndex bool, nodes []uint64, weights []float64, hash u
 // sortByDistance sorts nodes by hrw distance using provided swapper.
 // nodes contains hrw hashes. If it is nil, indices are used.
 func sortByDistance(l int, byIndex bool, nodes []uint64, hash uint64, swap func(i, j int)) {
-	s, ind, dist := newSorter(l, byIndex, nodes, hash, swap)
+	dist := make([]uint64, l)
-	s.less = func(i, j int) bool {
+	for i := 0; i < l; i++ {
-		return dist[ind[i]] < dist[ind[j]]
+		dist[i] = getDistance(byIndex, i, nodes, hash)
+	}
+
+	s := &sorter{
+		l: l,
+		swap: func(i, j int) {
+			swap(i, j)
+			dist[i], dist[j] = dist[j], dist[i]
+		},
+		less: func(i, j int) bool {
+			return dist[i] < dist[j]
+		},
 	}
 	sort.Sort(s)
 }