From a07797c166c3008d7520a046982dbf2fbd4fcec5 Mon Sep 17 00:00:00 2001
From: Christian Decker <decker.christian@gmail.com>
Date: Fri, 15 Apr 2022 14:24:09 +0200
Subject: [PATCH] features: Add function to unset a featurebit

Needed so we can blank optional bits when comparing channel_types.
---
 common/features.c | 11 +++++++++++
 common/features.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/common/features.c b/common/features.c
index 14c0a3914..5040c39ac 100644
--- a/common/features.c
+++ b/common/features.c
@@ -516,6 +516,17 @@ u8 *featurebits_or(const tal_t *ctx, const u8 *f1 TAKES, const u8 *f2 TAKES)
 	return result;
 }
 
+void featurebits_unset(u8 **ptr, size_t bit)
+{
+	size_t len = tal_count(*ptr);
+	if (bit / 8 >= len)
+		return;
+
+	(*ptr)[len - 1 - bit / 8] &= (0 << (bit % 8));
+
+	trim_features(ptr);
+}
+
 bool featurebits_eq(const u8 *f1, const u8 *f2)
 {
 	size_t len = tal_bytelen(f1);
diff --git a/common/features.h b/common/features.h
index 58b57c48f..d5da02fdf 100644
--- a/common/features.h
+++ b/common/features.h
@@ -73,6 +73,8 @@ void set_feature_bit(u8 **ptr, u32 bit);
 
 /* Given two featurebit vectors, combine them by applying a logical OR. */
 u8 *featurebits_or(const tal_t *ctx, const u8 *f1 TAKES, const u8 *f2 TAKES);
+/* Unset a given bit in a featurebits string */
+void featurebits_unset(u8 **ptr, size_t bit);
 
 /* Are these two feature bitsets functionally equal (one may have
  * trailing zeroes)? */