From 1d37b87da4192572b0ff18765db4cf756176a7de Mon Sep 17 00:00:00 2001
From: dignifiedquire <me@dignifiedquire.com>
Date: Thu, 20 Jan 2022 19:03:12 +0100
Subject: [PATCH] feat: add 32bit support

---
 .github/workflows/ci.yml | 13 ++++++------
 src/lib.rs               |  2 --
 src/scalar.rs            | 44 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5beffcb..235989c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,11 +30,6 @@ jobs:
             rust: nightly
             arch: aarch64
 
-          # 64-bit Linux/arm64
-          - target: aarch64-unknown-linux-gnu
-            rust: nightly
-            arch: aarch64
-
     runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
@@ -57,6 +52,8 @@ jobs:
           
           run: |
             $HOME/.cargo/bin/cargo test --release --target ${{ matrix.target }}
+            $HOME/.cargo/bin/cargo test --release --features portable --target ${{ matrix.target }}
+
   # Linux tests
   linux:
     needs: set-msrv
@@ -90,6 +87,7 @@ jobs:
         run: sudo apt-get install -y ocl-icd-opencl-dev
       - run: ${{ matrix.deps }}
       - run: cargo test --target ${{ matrix.target }}
+      - run: cargo test --target ${{ matrix.target }} --features portable
 
   # macOS tests
   macos:
@@ -110,6 +108,7 @@ jobs:
           target: x86_64-apple-darwin
           override: true
       - run: cargo test
+      - run: cargo test --features portable
 
  # Windows tests
   windows:
@@ -117,7 +116,8 @@ jobs:
     strategy:
       matrix:
         include:
-          - target: x86_64-pc-windows-gnu
+          # 64-bit Windows (MSVC)
+          - target: x86_64-pc-windows-msvc
             toolchain: stable
 
     runs-on: windows-latest
@@ -131,6 +131,7 @@ jobs:
           override: true
       - uses: msys2/setup-msys2@v2
       - run: cargo test --target ${{ matrix.target }}
+      - run: cargo test --target ${{ matrix.target }} --features portable
 
   clippy_check:
     runs-on: ubuntu-latest
diff --git a/src/lib.rs b/src/lib.rs
index e6c993a..1c23744 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,8 +8,6 @@
 
 #[cfg(not(target_endian = "little"))]
 compile_error!("blstrs is only supported on little endian architectures");
-#[cfg(not(target_pointer_width = "64"))]
-compile_error!("blstrs is only supported on 64bit architectures");
 
 #[macro_use]
 mod macros;
diff --git a/src/scalar.rs b/src/scalar.rs
index b224675..d5c7141 100644
--- a/src/scalar.rs
+++ b/src/scalar.rs
@@ -41,6 +41,19 @@ const MODULUS: [u64; 4] = [
     0x73ed_a753_299d_7d48,
 ];
 
+/// The modulus as u32 limbs.
+#[cfg(not(target_pointer_width = "64"))]
+const MODULUS_LIMBS_32: [u32; 8] = [
+    0x0000_0001,
+    0xffff_ffff,
+    0xfffe_5bfe,
+    0x53bd_a402,
+    0x09a1_d805,
+    0x3339_d808,
+    0x299d_7d48,
+    0x73ed_a753,
+];
+
 // Little-endian non-Montgomery form not reduced mod p.
 const MODULUS_REPR: [u8; 32] = [
     0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x5b, 0xfe, 0xff, 0x02, 0xa4, 0xbd, 0x53,
@@ -465,10 +478,17 @@ impl PrimeField for Scalar {
     }
 }
 
+#[cfg(not(target_pointer_width = "64"))]
+type ReprBits = [u32; 8];
+
+#[cfg(target_pointer_width = "64")]
+type ReprBits = [u64; 4];
+
 impl PrimeFieldBits for Scalar {
     // Representation in non-Montgomery form.
-    type ReprBits = [u64; 4];
+    type ReprBits = ReprBits;
 
+    #[cfg(target_pointer_width = "64")]
     fn to_le_bits(&self) -> FieldBits<Self::ReprBits> {
         let mut limbs = [0u64; 4];
         unsafe { blst_uint64_from_fr(limbs.as_mut_ptr(), &self.0) };
@@ -476,7 +496,29 @@ impl PrimeFieldBits for Scalar {
         FieldBits::new(limbs)
     }
 
+    #[cfg(not(target_pointer_width = "64"))]
+    fn to_le_bits(&self) -> FieldBits<Self::ReprBits> {
+        let bytes = self.to_bytes_le();
+        let limbs = [
+            u32::from_le_bytes(bytes[0..4].try_into().unwrap()),
+            u32::from_le_bytes(bytes[4..8].try_into().unwrap()),
+            u32::from_le_bytes(bytes[8..12].try_into().unwrap()),
+            u32::from_le_bytes(bytes[12..16].try_into().unwrap()),
+            u32::from_le_bytes(bytes[16..20].try_into().unwrap()),
+            u32::from_le_bytes(bytes[20..24].try_into().unwrap()),
+            u32::from_le_bytes(bytes[24..28].try_into().unwrap()),
+            u32::from_le_bytes(bytes[28..32].try_into().unwrap()),
+        ];
+        FieldBits::new(limbs)
+    }
+
     fn char_le_bits() -> FieldBits<Self::ReprBits> {
+        #[cfg(not(target_pointer_width = "64"))]
+        {
+            FieldBits::new(MODULUS_LIMBS_32)
+        }
+
+        #[cfg(target_pointer_width = "64")]
         FieldBits::new(MODULUS)
     }
 }