Fix #38 - support rust_decimal.

Cargo.toml

@@ -18,6 +18,7 @@ arrayvec = { version = "0.7", default-features = false, optional = true }
 bitcode_derive = { version = "0.6.3", path = "./bitcode_derive", optional = true }
 bytemuck = { version = "1.14", features = [ "min_const_generics", "must_cast" ] }
 glam = { version = ">=0.21", default-features = false, optional = true }
+rust_decimal = { version = "1.36", default-features = false, optional = true }
 serde = { version = "1.0", default-features = false, features = [ "alloc" ], optional = true }
 
 [dev-dependencies]
@@ -37,7 +38,7 @@ zstd = "0.13.0"
 
 [features]
 derive = [ "dep:bitcode_derive" ]
-std = [ "serde?/std", "glam?/std", "arrayvec?/std" ]
+std = [ "serde?/std", "glam?/std", "arrayvec?/std", "rust_decimal?/std" ]
 default = [ "derive", "std" ]
 
 [package.metadata.docs.rs]

fuzz/Cargo.toml

@@ -10,8 +10,9 @@ cargo-fuzz = true
 
 [dependencies]
 arrayvec = { version = "0.7", features = ["serde"] }
-bitcode = { path = "..", features = [ "arrayvec", "serde" ] }
+bitcode = { path = "..", features = [ "arrayvec", "serde", "rust_decimal" ] }
 libfuzzer-sys = "0.4"
+rust_decimal = "1.36.0"
 serde = { version ="1.0", features = [ "derive" ] }
 
 # Prevent this from interfering with workspaces

fuzz/fuzz_targets/fuzz.rs

@@ -9,6 +9,7 @@ use std::collections::{BTreeMap, HashMap};
 use std::fmt::Debug;
 use std::num::NonZeroU32;
 use std::time::Duration;
+use rust_decimal::Decimal;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddrV4, SocketAddr, SocketAddrV6};
 
 #[inline(never)]
@@ -209,6 +210,7 @@ fuzz_target!(|data: &[u8]| {
         ArrayString<70>,
         ArrayVec<u8, 5>,
         ArrayVec<u8, 70>,
+        Decimal,
         Duration,
         Ipv4Addr,
         Ipv6Addr,

src/ext/mod.rs

@@ -3,6 +3,8 @@ mod arrayvec;
 #[cfg(feature = "glam")]
 #[rustfmt::skip] // Makes impl_struct! calls way longer.
 mod glam;
+#[cfg(feature = "rust_decimal")]
+mod rust_decimal;
 
 #[allow(unused)]
 macro_rules! impl_struct {

src/ext/rust_decimal.rs

@@ -0,0 +1,109 @@
+use crate::{
+    convert::{self, impl_convert, ConvertFrom},
+    Decode, Encode,
+};
+use bytemuck::CheckedBitPattern;
+use rust_decimal::Decimal;
+type DecimalConversion = (u32, u32, u32, Flags);
+
+impl ConvertFrom<&Decimal> for DecimalConversion {
+    fn convert_from(value: &Decimal) -> Self {
+        let unpacked = value.unpack();
+        (
+            unpacked.lo,
+            unpacked.mid,
+            unpacked.hi,
+            Flags::new(unpacked.scale, unpacked.negative),
+        )
+    }
+}
+
+impl ConvertFrom<DecimalConversion> for Decimal {
+    fn convert_from(value: DecimalConversion) -> Self {
+        let scale = value.3.scale();
+        // Should make Decimal::from_parts faster, once it can be inlined,
+        // since it can skip division.
+        // Safety: impl CheckedBitPattern for Flags guarantees this.
+        unsafe {
+            if scale > 28 {
+                core::hint::unreachable_unchecked();
+            }
+        }
+        let mut ret = Self::from_parts(value.0, value.1, value.2, false, scale);
+        ret.set_sign_negative(value.3.negative());
+        ret
+    }
+}
+
+impl_convert!(Decimal, DecimalConversion);
+
+impl ConvertFrom<&Flags> for u8 {
+    fn convert_from(flags: &Flags) -> Self {
+        flags.0
+    }
+}
+
+impl Encode for Flags {
+    type Encoder = convert::ConvertIntoEncoder<u8>;
+}
+
+/// A u8 guaranteed to satisfy (flags >> 1) <= 28. Prevents Decimal::from_parts from misbehaving.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Flags(u8);
+
+impl Flags {
+    #[inline(always)]
+    fn new(scale: u32, negative: bool) -> Self {
+        Self((scale as u8) << 1 | negative as u8)
+    }
+
+    #[inline(always)]
+    fn scale(&self) -> u32 {
+        (self.0 >> 1) as u32
+    }
+
+    #[inline(always)]
+    fn negative(&self) -> bool {
+        self.0 & 1 == 1
+    }
+}
+
+// Safety: u8 and Flags have the same layout since Flags is #[repr(transparent)].
+unsafe impl CheckedBitPattern for Flags {
+    type Bits = u8;
+    #[inline(always)]
+    fn is_valid_bit_pattern(bits: &Self::Bits) -> bool {
+        (*bits >> 1) <= 28
+    }
+}
+
+impl<'a> Decode<'a> for Flags {
+    type Decoder = crate::int::CheckedIntDecoder<'a, Flags, u8>;
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{decode, encode};
+    use rust_decimal::Decimal;
+    use std::str::FromStr;
+
+    #[test]
+    fn rust_decimal() {
+        let vs = [
+            Decimal::from(0),
+            Decimal::from_f64_retain(-0f64).unwrap(),
+            Decimal::from(-1),
+            Decimal::from(1) / Decimal::from(2),
+            Decimal::from(1),
+            Decimal::from(999999999999999999u64),
+            Decimal::from_str("3.100").unwrap(),
+        ];
+        for v in vs {
+            let d = decode::<Decimal>(&encode(&v)).unwrap();
+            assert_eq!(d, v);
+            assert_eq!(d.is_sign_negative(), v.is_sign_negative());
+            assert_eq!(d.scale(), v.scale());
+        }
+    }
+}

src/serde/de.rs

@@ -120,8 +120,8 @@ macro_rules! specify {
                 #[rustfmt::skip]
                 fn cold<'de>(decoder: &mut SerdeDecoder<'de>, input: &mut &'de [u8]) -> Result<()> {
                     let &mut SerdeDecoder::Unspecified { length } = decoder else {
-                        type_changed!()
-                    };
+                            type_changed!()
+                        };
                     *decoder = SerdeDecoder::$variant(Default::default());
                     decoder.populate(input, length)
                 }
@@ -130,10 +130,10 @@ macro_rules! specify {
         }
         #[rustfmt::skip]
         let SerdeDecoder::$variant(d) = &mut *$self.decoder else {
-            // Safety: `cold` gets called when decoder isn't the correct decoder. `cold` either
-            // errors or sets lazy to the correct decoder.
-            unsafe { core::hint::unreachable_unchecked() };
-        };
+                // Safety: `cold` gets called when decoder isn't the correct decoder. `cold` either
+                // errors or sets lazy to the correct decoder.
+                unsafe { core::hint::unreachable_unchecked() };
+            };
         d
     }};
 }