From 81c729b83ee2b00e8f11acd2c9db6ae9aec4c0af Mon Sep 17 00:00:00 2001
From: dapplion <35266934+dapplion@users.noreply.github.com>
Date: Tue, 11 Jul 2023 22:22:37 +0200
Subject: [PATCH] Add limit churn feature

---
 specs/_features/limit_churn/beacon_chain.md | 55 +++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 specs/_features/limit_churn/beacon_chain.md

diff --git a/specs/_features/limit_churn/beacon_chain.md b/specs/_features/limit_churn/beacon_chain.md
new file mode 100644
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+Limit churn -- The Beacon Chain
+
+## Table of contents
+
+<!-- TOC -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+- [Introduction](#introduction)
+- [Preset](#preset)
+  - [Time parameters](#time-parameters)
+- [Helper functions](#helper-functions)
+  - [Predicates](#predicates)
+    - [`is_reusable_validator`](#is_reusable_validator)
+- [Beacon chain state transition function](#beacon-chain-state-transition-function)
+  - [Block processing](#block-processing)
+    - [Modified `get_index_for_new_validator`](#modified-get_index_for_new_validator)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+## Introduction
+
+This is the beacon chain specification to limit the max churn value, motivated to limit the validator active set growth rate.
+
+*Note:* This specification is built upon [Capella](../../capella/beacon_chain.md) and is under active development.
+
+## Configuration
+
+### Validator cycle
+
+| Name | Value |
+| - | - |
+| `MAX_PER_EPOCH_CHURN_LIMIT` | `uint64(12)` (= 12) |
+
+## Helper functions
+
+### Beacon state accessors
+
+#### modified `get_validator_churn_limit`
+
+```python
+def get_validator_churn_limit(state: BeaconState) -> uint64:
+    """
+    Return the validator churn limit for the current epoch.
+    """
+    active_validator_indices = get_active_validator_indices(state, get_current_epoch(state))
+    return min(
+      MAX_PER_EPOCH_CHURN_LIMIT,
+      max(
+        MIN_PER_EPOCH_CHURN_LIMIT,
+        uint64(len(active_validator_indices)) // CHURN_LIMIT_QUOTIENT
+      )
+    )
+```