add reserve_int

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bitbuffer"
-version = "0.9.8"
+version = "0.9.9"
 authors = ["Robin Appelman <robin@icewind.nl>"]
 edition = "2018"
 description = "Reading bit sequences from a byte slice"
@@ -21,4 +21,8 @@ iai = "0.1"
 name = "bench"
 harness = false
 
+[[bench]]
+name = "write"
+harness = false
+
 [workspace]

benches/write.rs

@@ -0,0 +1,15 @@
+use bitbuffer::{BitWriteStream, LittleEndian};
+use iai::black_box;
+
+fn write_int_le() {
+    let mut out = Vec::with_capacity(128);
+    {
+        let mut write = BitWriteStream::new(&mut out, LittleEndian);
+        for i in 0..128 {
+            write.write_sized(&black_box(i), 7).unwrap();
+        }
+    }
+    black_box(out);
+}
+
+iai::main!(write_int_le);

src/writestream.rs

@@ -349,4 +349,19 @@ where
         head.write_sized(&byte_len, length_bit_size)?;
         Ok(())
     }
+
+    /// Reserve the length to write an integer
+    pub fn reserve_int<Err: From<BitError>, F: Fn(&mut BitWriteStream<E>) -> Result<u64, Err>>(
+        &mut self,
+        length_bit_size: usize,
+        body_fn: F,
+    ) -> Result<(), Err> {
+        let (head, tail) = self.buffer.reserve(length_bit_size);
+        let mut head = BitWriteStream { buffer: head };
+        let mut tail = BitWriteStream { buffer: tail };
+
+        let head_int = body_fn(&mut tail)?;
+        head.write_sized(&head_int, length_bit_size)?;
+        Ok(())
+    }
 }