Add attribute docs

src/attributes.rs

@@ -33,6 +33,7 @@ enum DekuEnum {
 | Attribute | Scope | Description
 |-----------|------------------|------------
 | [endian](#endian) | top-level, field | Set the endianness
+| [bit_order](#bit_order) | top-level, field | Set the field representing the order in which to read the bits
 | [magic](#magic) | top-level | A magic value that must be present at the start of this struct/enum
 | [assert](#assert) | field | Assert a condition
 | [assert_eq](#assert_eq) | field | Assert equals on the field
@@ -141,6 +142,92 @@ assert_eq!(
 let value: Vec<u8> = value.try_into().unwrap();
 assert_eq!(&*data, value);
 ```
+# bit_order
+
+Specify the field or containers bit order. By default all bits are read in `Msb0` (Most significant bit) order.
+
+### Top-Level Example
+```rust
+# use deku::prelude::*;
+# use std::convert::{TryInto, TryFrom};
+# #[derive(Debug, DekuRead, DekuWrite, PartialEq)]
+#[deku(bit_order = "lsb")]
+pub struct SquashfsV3 {
+    #[deku(bits = "4")]
+    inode_type: u32,
+    #[deku(bits = "12")]
+    mode: u32,
+    #[deku(bits = "8")]
+    uid: u32,
+    #[deku(bits = "8")]
+    guid: u32,
+    mtime: u32,
+    inode_number: u32,
+}
+
+let data: &[u8] = &[
+    0x31, 0x12, 0x04, 0x05, 0x06, 0x00, 0x00, 0x00, 0x07, 0x00, 0x00, 0x00,
+];
+let header = SquashfsV3::try_from(data).unwrap();
+assert_eq!(
+    SquashfsV3 {
+        inode_type: 0x01,
+        mode: 0x123,
+        uid: 0x4,
+        guid: 0x5,
+        mtime: 0x6,
+        inode_number: 0x7
+    },
+    header,
+);
+```
+
+With endian-ness:
+```rust
+# use deku::prelude::*;
+# use std::convert::{TryInto, TryFrom};
+# #[derive(Debug, DekuRead, DekuWrite, PartialEq)]
+#[deku(endian = "big", bit_order = "lsb")]
+pub struct BigEndian {
+    #[deku(bits = "13")]
+    offset: u16,
+    #[deku(bits = "3")]
+    t: u8,
+}
+
+let data = vec![0x40, 0x40];
+let big_endian = BigEndian::try_from(data.as_ref()).unwrap();
+assert_eq!(
+    more_first,
+    BigEndian {
+        offset: 0x4000,
+        t: 2
+    }
+);
+
+let bytes = big_endian.to_bytes().unwrap();
+assert_eq!(bytes, data);
+````
+
+### Field Example
+```rust
+# use deku::prelude::*;
+# use std::convert::{TryInto, TryFrom};
+# #[derive(Debug, DekuRead, DekuWrite, PartialEq)]
+pub struct LsbField {
+    #[deku(bit_order = "lsb", bits = "13")]
+    offset: u16,
+    #[deku(bit_order = "lsb", bits = "3")]
+    t: u8,
+}
+
+let data = vec![0x40, 0x40];
+let more_first = LsbField::try_from(data.as_ref()).unwrap();
+assert_eq!(more_first, LsbField { offset: 0x40, t: 2 });
+
+let bytes = more_first.to_bytes().unwrap();
+assert_eq!(bytes, data);
+```
 
 # magic
 

src/ctx.rs

@@ -4,12 +4,12 @@
 use core::marker::PhantomData;
 use core::str::FromStr;
 
-/// An Bit Order
+/// Bit numbering
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum Order {
-    /// Big endian
+    /// Most significant bit
     Msb0,
-    /// Little endian
+    /// least significant bit
     Lsb0,
 }
 

tests/bit_order.rs

@@ -229,13 +229,30 @@ pub struct MoreFirst {
 fn test_bit_order_more_first() {
     let data = vec![0x40, 0x40];
     let more_first = MoreFirst::try_from(data.as_ref()).unwrap();
-    //                           bits: 13            3
     assert_eq!(more_first, MoreFirst { offset: 0x40, t: 2 });
 
     let bytes = more_first.to_bytes().unwrap();
     assert_eq_hex!(bytes, data);
 }
 
+#[derive(Debug, DekuRead, DekuWrite, PartialEq)]
+pub struct LsbField {
+    #[deku(bit_order = "lsb", bits = "13")]
+    offset: u16,
+    #[deku(bit_order = "lsb", bits = "3")]
+    t: u8,
+}
+
+#[test]
+fn test_bit_order_lsb_field() {
+    let data = vec![0x40, 0x40];
+    let more_first = LsbField::try_from(data.as_ref()).unwrap();
+    assert_eq!(more_first, LsbField { offset: 0x40, t: 2 });
+
+    let bytes = more_first.to_bytes().unwrap();
+    assert_eq_hex!(bytes, data);
+}
+
 #[test]
 fn test_bit_order_custom_reader_writer() {
     fn reader_lsb<R: std::io::Read>(reader: &mut Reader<R>) -> Result<(u16, u8), DekuError> {
@@ -309,7 +326,6 @@ pub struct MoreFirstBe {
 
 #[test]
 fn test_bit_order_more_first_be() {
-    env_logger::init();
     let data = vec![0x40, 0x40];
     let more_first = MoreFirstBe::try_from(data.as_ref()).unwrap();
     assert_eq!(