pre-allocate arrays

ids/short_set.go

@@ -57,15 +57,23 @@ func (ids *ShortSet) Remove(idList ...ShortID) {
 // Clear empties this set
 func (ids *ShortSet) Clear() { *ids = nil }
 
-// CappedList returns a list of length at most [size]. Size should be >= 0
+// CappedList returns a list of length at most [size].
+// Size should be >= 0. If size < 0, returns empty list.
 func (ids ShortSet) CappedList(size int) []ShortID {
-	idList := make([]ShortID, size)[:0]
+	if size < 0 {
+		return make([]ShortID, 0, 0)
+	}
+	if l := ids.Len(); l < size {
+		size = l
+	}
+	i := 0
+	idList := make([]ShortID, size)
 	for id := range ids {
-		if size <= 0 {
+		if i >= size {
 			break
 		}
-		size--
-		idList = append(idList, NewShortID(id))
+		idList[i] = NewShortID(id)
+		i++
 	}
 	return idList
 }

snow/validators/set.go

@@ -71,9 +71,10 @@ func (s *set) Set(vdrs []Validator) {
 }
 
 func (s *set) set(vdrs []Validator) {
-	s.vdrMap = make(map[[20]byte]int, len(vdrs))
-	s.vdrSlice = s.vdrSlice[:0]
-	s.sampler.Weights = s.sampler.Weights[:0]
+	lenVdrs := len(vdrs)
+	s.vdrMap = make(map[[20]byte]int, lenVdrs)
+	s.vdrSlice = make([]Validator, 0, lenVdrs)
+	s.sampler.Weights = make([]uint64, 0, lenVdrs)
 
 	for _, vdr := range vdrs {
 		s.add(vdr)

vms/platformvm/vm.go

@@ -18,6 +18,7 @@ import (
 	"github.com/ava-labs/gecko/snow/consensus/snowman"
 	"github.com/ava-labs/gecko/snow/engine/common"
 	"github.com/ava-labs/gecko/snow/validators"
+	"github.com/ava-labs/gecko/utils/codec"
 	"github.com/ava-labs/gecko/utils/crypto"
 	"github.com/ava-labs/gecko/utils/formatting"
 	"github.com/ava-labs/gecko/utils/logging"
@@ -26,7 +27,6 @@ import (
 	"github.com/ava-labs/gecko/utils/units"
 	"github.com/ava-labs/gecko/utils/wrappers"
 	"github.com/ava-labs/gecko/vms/components/ava"
-	"github.com/ava-labs/gecko/utils/codec"
 	"github.com/ava-labs/gecko/vms/components/core"
 	"github.com/ava-labs/gecko/vms/secp256k1fx"
 )
@@ -808,9 +808,11 @@ func (vm *VM) getValidators(validatorEvents *EventHeap) []validators.Validator {
 		validator.Wght = weight
 	}
 
-	vdrList := make([]validators.Validator, len(vdrMap))[:0]
+	vdrList := make([]validators.Validator, len(vdrMap), len(vdrMap))
+	i := 0
 	for _, validator := range vdrMap {
-		vdrList = append(vdrList, validator)
+		vdrList[i] = validator
+		i++
 	}
 	return vdrList
 }