M31 and CM31 Fields

.github/workflows/cairo-ci.yaml

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+name: Cairo workflow
+on:
+  push:
+    branches:
+      - main
+
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - auto_merge_enabled
+
+  merge_group:
+    types:
+      - checks_requested
+
+jobs:
+  scarb-test:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./stwo_cairo_verifier
+    steps:
+      - uses: actions/checkout@v3
+      - uses: software-mansion/setup-scarb@v1
+        with:
+          scarb-version: "2.6.4"
+      - run: scarb fmt --check
+      - run: scarb test

stwo_cairo_verifier/.gitignore

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+target

stwo_cairo_verifier/Scarb.lock

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+# Code generated by scarb DO NOT EDIT.
+version = 1
+
+[[package]]
+name = "stwo_cairo_verifier"
+version = "0.1.0"

stwo_cairo_verifier/Scarb.toml

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+[package]
+name = "stwo_cairo_verifier"
+version = "0.1.0"
+edition = "2023_11"
+
+# See more keys and their definitions at https://docs.swmansion.com/scarb/docs/reference/manifest.html
+
+[dependencies]

stwo_cairo_verifier/src/fields.cairo

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+pub mod m31;
+pub mod cm31;

stwo_cairo_verifier/src/fields/cm31.cairo

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+use super::m31::{M31, m31};
+
+#[derive(Copy, Drop, Debug, PartialEq, Eq)]
+pub struct CM31 {
+    a: M31,
+    b: M31,
+}
+
+pub impl CM31Add of core::traits::Add<CM31> {
+    fn add(lhs: CM31, rhs: CM31) -> CM31 {
+        CM31 { a: lhs.a + rhs.a, b: lhs.b + rhs.b }
+    }
+}
+pub impl CM31Sub of core::traits::Sub<CM31> {
+    fn sub(lhs: CM31, rhs: CM31) -> CM31 {
+        CM31 { a: lhs.a - rhs.a, b: lhs.b - rhs.b }
+    }
+}
+pub impl CM31Mul of core::traits::Mul<CM31> {
+    fn mul(lhs: CM31, rhs: CM31) -> CM31 {
+        CM31 { a: lhs.a * rhs.a - lhs.b * rhs.b, b: lhs.a * rhs.b + lhs.b * rhs.a }
+    }
+}
+pub impl CM31Zero of core::num::traits::Zero<CM31> {
+    fn zero() -> CM31 {
+        cm31(0, 0)
+    }
+    fn is_zero(self: @CM31) -> bool {
+        (*self).a.is_zero() && (*self).b.is_zero()
+    }
+    fn is_non_zero(self: @CM31) -> bool {
+        (*self).a.is_non_zero() || (*self).b.is_non_zero()
+    }
+}
+pub impl CM31One of core::num::traits::One<CM31> {
+    fn one() -> CM31 {
+        cm31(1, 0)
+    }
+    fn is_one(self: @CM31) -> bool {
+        (*self).a.is_one() && (*self).b.is_zero()
+    }
+    fn is_non_one(self: @CM31) -> bool {
+        (*self).a.is_non_one() || (*self).b.is_non_zero()
+    }
+}
+pub impl M31IntoCM31 of core::traits::Into<M31, CM31> {
+    fn into(self: M31) -> CM31 {
+        CM31 { a: self, b: m31(0) }
+    }
+}
+pub impl CM31Neg of Neg<CM31> {
+    fn neg(a: CM31) -> CM31 {
+        CM31 { a: -a.a, b: -a.b }
+    }
+}
+
+pub fn cm31(a: u32, b: u32) -> CM31 {
+    CM31 { a: m31(a), b: m31(b) }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::{cm31};
+    use super::super::m31::{m31, P};
+
+    #[test]
+    fn test_m31() {
+        let cm0 = cm31(1, 2);
+        let cm1 = cm31(4, 5);
+        let m = m31(8);
+        let cm = cm31(8, 0);
+        let cm0_x_cm1 = cm31(P - 6, 13);
+
+        assert_eq!(cm0 + cm1, cm31(5, 7));
+        assert_eq!(cm1 + m.into(), cm1 + cm);
+        assert_eq!(cm0 * cm1, cm0_x_cm1);
+        assert_eq!(cm1 * m.into(), cm1 * cm);
+        assert_eq!(-cm0, cm31(P - 1, P - 2));
+        assert_eq!(cm0 - cm1, cm31(P - 3, P - 3));
+        assert_eq!(cm1 - m.into(), cm1 - cm);
+    }
+}

stwo_cairo_verifier/src/fields/m31.cairo

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+use core::option::OptionTrait;
+use core::traits::TryInto;
+use core::result::ResultTrait;
+
+pub const P: u32 = 0x7fffffff;
+const P32NZ: NonZero<u32> = 0x7fffffff;
+const P64NZ: NonZero<u64> = 0x7fffffff;
+
+#[derive(Copy, Drop, Debug, PartialEq, Eq)]
+pub struct M31 {
+    inner: u32
+}
+
+#[generate_trait]
+pub impl M31Impl of M31Trait {
+    fn reduce_u32(val: u32) -> M31 {
+        let (_, res) = core::integer::u32_safe_divmod(val, P32NZ);
+        M31 { inner: res.try_into().unwrap() }
+    }
+
+    fn reduce_u64(val: u64) -> M31 {
+        let (_, res) = core::integer::u64_safe_divmod(val, P64NZ);
+        M31 { inner: res.try_into().unwrap() }
+    }
+}
+pub impl M31Add of core::traits::Add<M31> {
+    fn add(lhs: M31, rhs: M31) -> M31 {
+        let res = lhs.inner + rhs.inner;
+        let res = core::integer::u32_overflowing_sub(res, P).unwrap_or(res);
+        M31 { inner: res }
+    }
+}
+pub impl M31Sub of core::traits::Sub<M31> {
+    fn sub(lhs: M31, rhs: M31) -> M31 {
+        match core::integer::u32_overflowing_sub(lhs.inner, rhs.inner) {
+            Result::Ok(res) => M31 { inner: res },
+            Result::Err(res) => M31 { inner: core::integer::u32_wrapping_add(res, P) }
+        }
+    }
+}
+pub impl M31Mul of core::traits::Mul<M31> {
+    fn mul(lhs: M31, rhs: M31) -> M31 {
+        M31Impl::reduce_u64(core::integer::u32_wide_mul(lhs.inner, rhs.inner))
+    }
+}
+pub impl M31Zero of core::num::traits::Zero<M31> {
+    fn zero() -> M31 {
+        M31 { inner: 0 }
+    }
+    fn is_zero(self: @M31) -> bool {
+        *self.inner == 0
+    }
+    fn is_non_zero(self: @M31) -> bool {
+        *self.inner != 0
+    }
+}
+pub impl M31One of core::num::traits::One<M31> {
+    fn one() -> M31 {
+        M31 { inner: 1 }
+    }
+    fn is_one(self: @M31) -> bool {
+        *self.inner == 1
+    }
+    fn is_non_one(self: @M31) -> bool {
+        *self.inner != 1
+    }
+}
+pub impl M31Neg of Neg<M31> {
+    fn neg(a: M31) -> M31 {
+        if a.inner == 0 {
+            M31 { inner: 0 }
+        } else {
+            M31 { inner: P - a.inner }
+        }
+    }
+}
+
+pub fn m31(val: u32) -> M31 {
+    M31Impl::reduce_u32(val)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{m31, P};
+
+    #[test]
+    fn test_m31() {
+        assert_eq!(m31(P), m31(0));
+        assert_eq!(m31(P + 1), m31(1));
+        assert_eq!(m31(1) + m31(2), m31(3));
+        assert_eq!(m31(3) - m31(2), m31(1));
+        assert_eq!(m31(P - 1) + m31(1), m31(0));
+        assert_eq!(m31(0) - m31(1), m31(P - 1));
+        assert_eq!(m31(0) - m31(P - 1), m31(1));
+    }
+}

stwo_cairo_verifier/src/lib.cairo

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+mod fields;
+
+fn main() {}