implement bitfield for enum with a width

If we know the width of an enum type, we don't need 'power of 2' number
of variants.

BUG=None
TEST=cargo test

Change-Id: I8148b28f86bb8e4fd4f67d8a6382fc713dad1439
Reviewed-on: https://chromium-review.googlesource.com/1530455
Commit-Ready: Jingkui Wang <jkwang@google.com>
Tested-by: Jingkui Wang <jkwang@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/bit_field/tests/test_enum.rs b/bit_field/tests/test_enum.rs
index d926d9c..8746b06 100644
--- a/bit_field/tests/test_enum.rs
+++ b/bit_field/tests/test_enum.rs
@@ -12,10 +12,21 @@ enum TwoBits {
 }
 
 #[bitfield]
+#[bits = 3]
+#[derive(Debug, PartialEq)]
+enum ThreeBits {
+    Zero = 0b00,
+    One = 0b01,
+    Two = 0b10,
+    Three = 0b111,
+}
+
+#[bitfield]
 struct Struct {
     prefix: BitField1,
     two_bits: TwoBits,
-    suffix: BitField5,
+    three_bits: ThreeBits,
+    suffix: BitField2,
 }
 
 #[test]
@@ -30,5 +41,10 @@ fn test_enum() {
 
     s.set(0, 8, 0b_1010_1010);
     //                   ^^ TwoBits
+    //               ^^_^ Three Bits.
     assert_eq!(s.get_two_bits(), TwoBits::One);
+    assert_eq!(s.get_three_bits().unwrap_err().raw_val(), 0b101);
+
+    s.set_three_bits(ThreeBits::Two);
+    assert_eq!(s.get(0, 8), 0b_1001_0010);
 }