From 36e9edd654f8e0166a74f174cafcdb426795a33e Mon Sep 17 00:00:00 2001
From: Preston Van Loon <preston@prysmaticlabs.com>
Date: Wed, 19 May 2021 12:11:48 -0400
Subject: [PATCH] Minor changes from hf1 branch (#8906)

* Copy new slot helpers from hf1 branch

* Make HandleEth1DataSlice public for altair
---
 beacon-chain/core/helpers/BUILD.bazel         |  1 +
 beacon-chain/core/helpers/slot_epoch.go       |  8 +++++
 beacon-chain/core/helpers/slot_epoch_test.go  | 36 +++++++++++++++++++
 .../state/stateV0/field_trie_helpers.go       |  5 +--
 beacon-chain/state/stateV0/helpers_test.go    |  3 +-
 5 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/beacon-chain/core/helpers/BUILD.bazel b/beacon-chain/core/helpers/BUILD.bazel
index c0714ae89a..45ba92a96b 100644
--- a/beacon-chain/core/helpers/BUILD.bazel
+++ b/beacon-chain/core/helpers/BUILD.bazel
@@ -27,6 +27,7 @@ go_library(
         "//shared/keystore:__pkg__",
         "//shared/p2putils:__pkg__",
         "//shared/testutil:__pkg__",
+        "//shared/testutil/altair:__pkg__",
         "//slasher:__subpackages__",
         "//spectest:__subpackages__",
         "//tools:__subpackages__",
diff --git a/beacon-chain/core/helpers/slot_epoch.go b/beacon-chain/core/helpers/slot_epoch.go
index b6374105aa..088b6dec0d 100644
--- a/beacon-chain/core/helpers/slot_epoch.go
+++ b/beacon-chain/core/helpers/slot_epoch.go
@@ -193,3 +193,11 @@ func VotingPeriodStartTime(genesis uint64, slot types.Slot) uint64 {
 	startTime := uint64((slot - slot.ModSlot(slots)).Mul(params.BeaconConfig().SecondsPerSlot))
 	return genesis + startTime
 }
+
+// PrevSlot returns previous slot, with an exception in slot 0 to prevent underflow.
+func PrevSlot(slot types.Slot) types.Slot {
+	if slot > 0 {
+		return slot.Sub(1)
+	}
+	return 0
+}
diff --git a/beacon-chain/core/helpers/slot_epoch_test.go b/beacon-chain/core/helpers/slot_epoch_test.go
index 2c539e3570..8963116e78 100644
--- a/beacon-chain/core/helpers/slot_epoch_test.go
+++ b/beacon-chain/core/helpers/slot_epoch_test.go
@@ -345,3 +345,39 @@ func TestValidateSlotClock_HandlesBadSlot(t *testing.T) {
 	assert.ErrorContains(t, "which exceeds max allowed value relative to the local clock", ValidateSlotClock(types.Slot(2*MaxSlotBuffer+1), uint64(genTime)), "no error from bad slot")
 	assert.ErrorContains(t, "which exceeds max allowed value relative to the local clock", ValidateSlotClock(1<<63, uint64(genTime)), "no error from bad slot")
 }
+
+func TestPrevSlot(t *testing.T) {
+	tests := []struct {
+		name string
+		slot types.Slot
+		want types.Slot
+	}{
+		{
+			name: "no underflow",
+			slot: 0,
+			want: 0,
+		},
+		{
+			name: "slot 1",
+			slot: 1,
+			want: 0,
+		},
+		{
+			name: "slot 2",
+			slot: 2,
+			want: 1,
+		},
+		{
+			name: "max",
+			slot: 1<<64 - 1,
+			want: 1<<64 - 1 - 1,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := PrevSlot(tt.slot); got != tt.want {
+				t.Errorf("PrevSlot() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/beacon-chain/state/stateV0/field_trie_helpers.go b/beacon-chain/state/stateV0/field_trie_helpers.go
index 0999c3af06..c64326602c 100644
--- a/beacon-chain/state/stateV0/field_trie_helpers.go
+++ b/beacon-chain/state/stateV0/field_trie_helpers.go
@@ -44,7 +44,7 @@ func fieldConverters(field fieldIndex, indices []uint64, elements interface{}, c
 			return nil, errors.Errorf("Wanted type of %v but got %v",
 				reflect.TypeOf([]*ethpb.Eth1Data{}).Name(), reflect.TypeOf(elements).Name())
 		}
-		return handleEth1DataSlice(val, indices, convertAll)
+		return HandleEth1DataSlice(val, indices, convertAll)
 	case validators:
 		val, ok := elements.([]*ethpb.Validator)
 		if !ok {
@@ -64,7 +64,8 @@ func fieldConverters(field fieldIndex, indices []uint64, elements interface{}, c
 	}
 }
 
-func handleEth1DataSlice(val []*ethpb.Eth1Data, indices []uint64, convertAll bool) ([][32]byte, error) {
+// HandleEth1DataSlice processes a list of eth1data and indices into the appropriate roots.
+func HandleEth1DataSlice(val []*ethpb.Eth1Data, indices []uint64, convertAll bool) ([][32]byte, error) {
 	length := len(indices)
 	if convertAll {
 		length = len(val)
diff --git a/beacon-chain/state/stateV0/helpers_test.go b/beacon-chain/state/stateV0/helpers_test.go
index ce8181cd1c..2faf46fb2b 100644
--- a/beacon-chain/state/stateV0/helpers_test.go
+++ b/beacon-chain/state/stateV0/helpers_test.go
@@ -18,6 +18,7 @@ func Test_handlePendingAttestation_OutOfRange(t *testing.T) {
 func Test_handleEth1DataSlice_OutOfRange(t *testing.T) {
 	items := make([]*ethpb.Eth1Data, 1)
 	indices := []uint64{3}
-	_, err := handleEth1DataSlice(items, indices, false)
+	_, err := HandleEth1DataSlice(items, indices, false)
 	assert.ErrorContains(t, "index 3 greater than number of items in eth1 data slice 1", err)
+
 }