cairo_lang_utils/

bigint.rs

#[cfg(test)]
#[path = "bigint_tests/mod.rs"]
mod test;

#[cfg(all(not(feature = "std"), feature = "serde"))]
use alloc::{format, string::String};

#[cfg(feature = "serde")]
use num_bigint::ToBigInt;
use num_bigint::{BigInt, BigUint};
#[cfg(feature = "serde")]
use num_traits::{Num, Signed};

/// A wrapper for BigUint that serializes as hex.
#[derive(Clone, Default, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize), serde(transparent))]
pub struct BigUintAsHex {
    /// A field element that encodes the signature of the called function.
    #[cfg_attr(
        feature = "serde",
        serde(serialize_with = "serialize_big_uint", deserialize_with = "deserialize_big_uint")
    )]
    pub value: BigUint,
}

#[cfg(feature = "serde")]
fn deserialize_from_str<'a, D>(s: &str) -> Result<BigUint, D::Error>
where
    D: serde::Deserializer<'a>,
{
    match s.strip_prefix("0x") {
        Some(num_no_prefix) => BigUint::from_str_radix(num_no_prefix, 16)
            .map_err(|error| serde::de::Error::custom(format!("{error}"))),
        None => Err(serde::de::Error::custom(format!(
            "{s} does not start with `0x`, which is missing."
        ))),
    }
}

#[cfg(feature = "serde")]
pub fn serialize_big_uint<S>(num: &BigUint, serializer: S) -> Result<S::Ok, S::Error>
where
    S: serde::Serializer,
{
    serializer.serialize_str(&format!("{num:#x}"))
}

#[cfg(feature = "serde")]
pub fn deserialize_big_uint<'a, D>(deserializer: D) -> Result<BigUint, D::Error>
where
    D: serde::Deserializer<'a>,
{
    let s = &<String as serde::Deserialize>::deserialize(deserializer)?;
    deserialize_from_str::<D>(s)
}

// A wrapper for BigInt that serializes as hex.
#[derive(Default, Clone, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize), serde(transparent))]
#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
pub struct BigIntAsHex {
    /// A field element that encodes the signature of the called function.
    #[cfg_attr(
        feature = "serde",
        serde(serialize_with = "serialize_big_int", deserialize_with = "deserialize_big_int")
    )]
    #[cfg_attr(feature = "schemars", schemars(schema_with = "big_int_schema"))]
    pub value: BigInt,
}

// BigInt doesn't implement JsonSchema, so we need to manually define it.
#[cfg(feature = "schemars")]
fn big_int_schema(gen: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
    use schemars::JsonSchema;

    #[allow(dead_code)]
    #[allow(clippy::enum_variant_names)]
    #[derive(JsonSchema)]
    pub enum Sign {
        Minus,
        NoSign,
        Plus,
    }

    #[allow(dead_code)]
    #[derive(JsonSchema)]
    pub struct BigUint {
        data: Vec<u64>, // BigDigit is u64 or u32.
    }

    #[allow(dead_code)]
    #[derive(JsonSchema)]
    struct BigInt {
        sign: Sign,
        data: BigUint,
    }

    gen.subschema_for::<BigInt>()
}

impl<T: Into<BigInt>> From<T> for BigIntAsHex {
    fn from(x: T) -> Self {
        Self { value: x.into() }
    }
}

#[cfg(feature = "serde")]
pub fn serialize_big_int<S>(num: &BigInt, serializer: S) -> Result<S::Ok, S::Error>
where
    S: serde::ser::Serializer,
{
    serializer.serialize_str(&format!(
        "{}{:#x}",
        if num.is_negative() { "-" } else { "" },
        num.magnitude()
    ))
}

#[cfg(feature = "serde")]
pub fn deserialize_big_int<'a, D>(deserializer: D) -> Result<BigInt, D::Error>
where
    D: serde::de::Deserializer<'a>,
{
    use core::ops::Neg;

    let s = &<String as serde::Deserialize>::deserialize(deserializer)?;
    match s.strip_prefix('-') {
        Some(abs_value) => Ok(deserialize_from_str::<D>(abs_value)?.to_bigint().unwrap().neg()),
        None => Ok(deserialize_from_str::<D>(s)?.to_bigint().unwrap()),
    }
}

#[cfg(feature = "parity-scale-codec")]
mod impl_parity_scale_codec {
    #[cfg(not(feature = "std"))]
    use alloc::vec;

    use parity_scale_codec::{Decode, Encode};

    use super::*;

    impl Encode for BigIntAsHex {
        fn size_hint(&self) -> usize {
            // sign + len packed in the same byte, it allows numbers of byte size up to 63 (2**504),
            // data.
            let bits = self.value.bits() as usize;
            core::mem::size_of::<u8>() + bits / 8 + if bits % 8 != 0 { 1 } else { 0 }
        }

        /// /!\ Warning this function panics if the number encoded is too big (>= 2**504)
        fn encode_to<T: parity_scale_codec::Output + ?Sized>(&self, dest: &mut T) {
            let (sign, data) = self.value.to_bytes_le();
            assert!(data.len() <= 63, "Can't encode numbers longer than 63 bytes");
            // Pack sign + number byte size.
            ((match sign {
                num_bigint::Sign::Minus => 0u8,
                num_bigint::Sign::NoSign => 1u8,
                num_bigint::Sign::Plus => 2u8,
            } << 6)
                + data.len() as u8)
                .encode_to(dest);
            dest.write(&data);
        }
    }

    impl Decode for BigIntAsHex {
        fn decode<I: parity_scale_codec::Input>(
            input: &mut I,
        ) -> Result<Self, parity_scale_codec::Error> {
            let sign_and_len = input.read_byte()?;
            let sign = match sign_and_len >> 6 {
                0u8 => num_bigint::Sign::Minus,
                1u8 => num_bigint::Sign::NoSign,
                2u8 => num_bigint::Sign::Plus,
                _ => {
                    return Err(parity_scale_codec::Error::from("Bad sign encoding."));
                }
            };
            let len = sign_and_len & 0b00111111;
            let mut buffer = vec![0; len as usize];
            input.read(&mut buffer)?;
            Ok(Self { value: BigInt::from_bytes_le(sign, buffer.as_slice()) })
        }
    }
}