From 3067c3585d36f0b7c87ac21edb047b340e31f219 Mon Sep 17 00:00:00 2001
From: Jan-Paul Bultmann
 <74891396+somethingelseentirely@users.noreply.github.com>
Date: Wed, 23 Jul 2025 18:05:50 +0200
Subject: [PATCH] Add from_bit constructor to BitVectorBuilder

---
 CHANGELOG.md          |  1 +
 src/bit_vector/mod.rs | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 54111dc..101dd5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@
 - Replaced the old `BitVector` with the generic `BitVector<I>` and renamed the
   mutable variant to `RawBitVector`.
 - Extended `BitVectorBuilder` with `push_bits` and `set_bit` APIs.
+- Added `from_bit` constructor on `BitVectorBuilder` for repeating a single bit.
 - `DacsByte` now stores level data as zero-copy `View<[u8]>` values.
 - Added `get_bits` methods to `BitVectorData` and `BitVector`.
 - Added `scripts/devtest.sh` and `scripts/preflight.sh` for testing and
diff --git a/src/bit_vector/mod.rs b/src/bit_vector/mod.rs
index 82b3278..b105b71 100644
--- a/src/bit_vector/mod.rs
+++ b/src/bit_vector/mod.rs
@@ -138,6 +138,22 @@ impl BitVectorBuilder {
         Self::default()
     }
 
+    /// Creates a builder that stores `len` copies of `bit`.
+    pub fn from_bit(bit: bool, len: usize) -> Self {
+        if len == 0 {
+            return Self::default();
+        }
+        let word = if bit { usize::MAX } else { 0 };
+        let num_words = (len + WORD_LEN - 1) / WORD_LEN;
+        let mut words = vec![word; num_words];
+        let shift = len % WORD_LEN;
+        if shift != 0 {
+            let mask = (1 << shift) - 1;
+            *words.last_mut().unwrap() &= mask;
+        }
+        Self { words, len }
+    }
+
     /// Pushes a single bit.
     pub fn push_bit(&mut self, bit: bool) {
         let pos_in_word = self.len % WORD_LEN;
@@ -590,6 +606,14 @@ mod tests {
         assert_eq!(bv.data.get_bits(61, 7).unwrap(), 0b0111110);
     }
 
+    #[test]
+    fn builder_from_bit() {
+        let builder = BitVectorBuilder::from_bit(true, 5);
+        let bv: BitVector<NoIndex> = builder.freeze::<NoIndex>();
+        assert_eq!(bv.len(), 5);
+        assert_eq!(bv.num_ones(), 5);
+    }
+
     #[test]
     fn iter_collects() {
         let data = BitVectorData::from_bits([true, false, true]);