feat: convert directly between C and Go arrays

bench_test.go

@@ -14,6 +14,7 @@ var (
 	addr     = cell.String()
 	geoBndry CellBoundary
 	cells    []Cell
+	disks    [][]Cell
 )
 
 func BenchmarkToString(b *testing.B) {
@@ -29,32 +30,48 @@ func BenchmarkFromString(b *testing.B) {
 	}
 }
 
-func BenchmarkToGeoRes15(b *testing.B) {
+func BenchmarkCellToLatLng(b *testing.B) {
 	for n := 0; n < b.N; n++ {
 		geo, _ = CellToLatLng(cell)
 	}
 }
 
-func BenchmarkFromGeoRes15(b *testing.B) {
+func BenchmarkLatLngToCell(b *testing.B) {
 	for n := 0; n < b.N; n++ {
 		cell, _ = LatLngToCell(geo, 15)
 	}
 }
 
-func BenchmarkToGeoBndryRes15(b *testing.B) {
+func BenchmarkCellToBoundary(b *testing.B) {
 	for n := 0; n < b.N; n++ {
 		geoBndry, _ = CellToBoundary(cell)
 	}
 }
 
-func BenchmarkHexRange(b *testing.B) {
+func BenchmarkGridDisk(b *testing.B) {
 	for n := 0; n < b.N; n++ {
 		cells, _ = cell.GridDisk(10)
 	}
 }
 
+func BenchmarkGridRing(b *testing.B) {
+	for range b.N {
+		cells, _ = cell.GridRing(10)
+	}
+}
+
 func BenchmarkPolyfill(b *testing.B) {
 	for n := 0; n < b.N; n++ {
-		cells, _ = PolygonToCells(validGeoPolygonHoles, 15)
+		cells, _ = PolygonToCells(validGeoPolygonHoles, 13)
+	}
+}
+
+func BenchmarkGridDisksUnsafe(b *testing.B) {
+	cells, _ = PolygonToCells(validGeoPolygonHoles, 12)
+
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		disks, _ = GridDisksUnsafe(cells, 10)
 	}
 }

h3.go

@@ -1176,18 +1176,14 @@ func intPow(n, m int) int {
 }
 
 func cellsFromC(chs []C.H3Index, prune, refit bool) []Cell {
-	// OPT: This could be more efficient if we unsafely cast the C array to a
-	// []H3Index.
-	out := make([]Cell, 0, len(chs))
-
-	for i := range chs {
-		if prune && chs[i] <= 0 {
+	in := unsafe.Slice((*Cell)(unsafe.Pointer(&chs[0])), len(chs))
+	out := in[:0]
+	for i := range in {
+		if prune && in[i] <= 0 {
 			continue
 		}
-
-		out = append(out, Cell(chs[i]))
+		out = append(out, in[i])
 	}
-
 	if refit {
 		// Some algorithms require a maximum sized array, but only use a subset
 		// of the memory.  refit sizes the slice to the last non-empty element.
@@ -1197,7 +1193,6 @@ func cellsFromC(chs []C.H3Index, prune, refit bool) []Cell {
 			}
 		}
 	}
-
 	return out
 }
 
@@ -1216,14 +1211,7 @@ func edgesFromC(chs []C.H3Index) []DirectedEdge {
 }
 
 func cellsToC(chs []Cell) []C.H3Index {
-	// OPT: This could be more efficient if we unsafely cast the array to a
-	// []C.H3Index.
-	out := make([]C.H3Index, len(chs))
-	for i := range chs {
-		out[i] = C.H3Index(chs[i])
-	}
-
-	return out
+	return unsafe.Slice((*C.H3Index)(unsafe.Pointer(&chs[0])), len(chs))
 }
 
 func intsFromC(chs []C.int) []int {