Fix #38 - support rust_decimal.

Author: finnbear

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 = "1.36.0", default-features = false, optional = true }
 serde = { version = "1.0", default-features = false, features = [ "alloc" ], optional = true }
 
 [dev-dependencies]
@@ -37,8 +38,8 @@ zstd = "0.13.0"
 
 [features]
 derive = [ "dep:bitcode_derive" ]
-std = [ "serde?/std", "glam?/std", "arrayvec?/std" ]
-default = [ "derive", "std" ]
+std = [ "serde?/std", "glam?/std", "arrayvec?/std", "rust_decimal?/std" ]
+default = [ "derive", "std", "rust_decimal" ]
 
 [package.metadata.docs.rs]
 features = [ "derive", "serde", "std" ]
@@ -48,4 +49,4 @@ features = [ "derive", "serde", "std" ]
 #lto = true
 
 [lints.rust]
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(fuzzing)'] }
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(fuzzing)'] }

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
@@ -22,4 +23,4 @@ members = ["."]
 name = "fuzz"
 path = "fuzz_targets/fuzz.rs"
 test = false
-doc = false
+doc = false

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/derive/mod.rs

@@ -5,7 +5,7 @@ use alloc::vec::Vec;
 use core::num::NonZeroUsize;
 
 mod array;
-mod convert;
+pub(crate) mod convert;
 mod duration;
 mod empty;
 mod impls;

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 +1,84 @@
+use crate::{
+    convert::{self, 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 {
+        Self::from_parts(
+            value.0,
+            value.1,
+            value.2,
+            value.3.negative(),
+            value.3.scale(),
+        )
+    }
+}
+
+impl Encode for Decimal {
+    type Encoder = convert::ConvertIntoEncoder<DecimalConversion>;
+}
+impl<'a> Decode<'a> for Decimal {
+    type Decoder = convert::ConvertFromDecoder<'a, 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>;
+}

src/serde/de.rs

@@ -119,19 +119,19 @@ macro_rules! specify {
                 #[cold]
                 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::$variant(Default::default());
                     decoder.populate(input, length)
                 }
                 cold(&mut *$self.decoder, &mut *$self.input)?;
             }
         }
         let SerdeDecoder::$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
     }};
 }