Add write_bytes_only feature

Cargo.toml

@@ -27,6 +27,11 @@ logging = ["deku_derive/logging", "log"]
 const_generics = []
 ## Enable container.read_cache by default when a `Container` is created
 read_cache = []
+## Disable writing bits, adding performance to writing bytes
+##
+## This is especially important in order to inline writer::write_bytes(..) and DekuWriter::to_writer(..)
+## whenever possible
+write_bytes_only = []
 
 [dependencies]
 deku_derive = { version = "^0.16.0", path = "deku-derive", default-features = false}

src/impls/primitive.rs

@@ -647,7 +647,7 @@ macro_rules! ImplDekuWrite {
 
         // Only have `endian`, return all input
         impl DekuWrite<Endian> for $typ {
-            #[inline(always)]
+            #[inline]
             fn write(
                 &self,
                 output: &mut BitVec<u8, Msb0>,
@@ -663,7 +663,7 @@ macro_rules! ImplDekuWrite {
         }
 
         impl DekuWriter<Endian> for $typ {
-            #[inline(always)]
+            #[inline]
             fn to_writer<W: Write>(
                 &self,
                 writer: &mut Writer<W>,

src/writer.rs

@@ -56,17 +56,25 @@ impl<W: Write> Writer<W> {
     pub fn write_bytes(&mut self, buf: &[u8]) -> Result<(), DekuError> {
         #[cfg(feature = "logging")]
         log::trace!("writing {} bytes", buf.len());
-        if !self.leftover.is_empty() {
-            #[cfg(feature = "logging")]
-            log::trace!("leftover exists");
-            // TODO: we could check here and only send the required bits to finish the byte?
-            // (instead of sending the entire thing)
-            self.write_bits(&mut BitVec::from_slice(buf))?;
-        } else {
+
+        if cfg!(feature = "write_bytes_only") {
             if let Err(_) = self.inner.write_all(buf) {
                 return Err(DekuError::WriteError);
             }
             self.bits_written = buf.len() * 8;
+        } else {
+            if self.leftover.is_empty() {
+                if let Err(_) = self.inner.write_all(buf) {
+                    return Err(DekuError::WriteError);
+                }
+                self.bits_written = buf.len() * 8;
+            } else {
+                #[cfg(feature = "logging")]
+                log::trace!("leftover exists");
+                // TODO: we could check here and only send the required bits to finish the byte?
+                // (instead of sending the entire thing)
+                self.write_bits(&mut BitVec::from_slice(buf))?;
+            }
         }
 
         Ok(())