feat(starknet_os): integrate to_bytes and serialize_blob

Author: dorimedini-starkware

Cargo.lock

@@ -98,6 +98,7 @@ blockifier = { path = "crates/blockifier", version = "0.0.0" }
 blockifier_test_utils = { path = "crates/blockifier_test_utils", version = "0.0.0" }
 byteorder = "1.4.3"
 bytes = "1"
+c-kzg = "1.0.3"
 cached = "0.44.0"
 cairo-felt = "0.9.1"
 cairo-lang-casm = "2.10.0"

Cargo.toml

@@ -18,6 +18,7 @@ testing = ["blockifier/testing"]
 
 [dependencies]
 blockifier.workspace = true
+c-kzg.workspace = true
 cairo-lang-starknet-classes.workspace = true
 cairo-vm = { workspace = true, features = ["extensive_hints"] }
 indexmap.workspace = true

crates/starknet_os/Cargo.toml

@@ -1,23 +1,46 @@
 use std::num::ParseIntError;
 
 use blockifier::utils::usize_from_u32;
+use c_kzg::BYTES_PER_FIELD_ELEMENT;
 use num_bigint::BigInt;
 use num_traits::One;
 
 #[allow(dead_code)]
 pub(crate) const BLS_PRIME: &str =
     "52435875175126190479447740508185965837690552500527637822603658699938581184513";
+const FIELD_ELEMENTS_PER_BLOB: usize = 4096;
 
 #[derive(Debug, thiserror::Error)]
 pub enum FftError {
     #[error("Group is missing last element.")]
     GroupMissingLastElement,
     #[error(transparent)]
     InvalidBinaryToUsize(ParseIntError),
+    #[error("Blob size must be {FIELD_ELEMENTS_PER_BLOB}, got {0}.")]
+    InvalidBlobSize(usize),
     #[error("Invalid coefficients length (must be a power of two): {0}.")]
     InvalidCoeffsLength(usize),
 }
 
+fn to_bytes(x: &BigInt, length: usize) -> Vec<u8> {
+    let mut bytes = x.to_bytes_be().1;
+    let padding = length.saturating_sub(bytes.len());
+    if padding > 0 {
+        let mut padded_bytes = std::iter::repeat(0u8).take(padding).collect::<Vec<u8>>();
+        padded_bytes.extend(bytes);
+        bytes = padded_bytes;
+    }
+    bytes
+}
+
+#[allow(dead_code)]
+fn serialize_blob(blob: &[BigInt]) -> Result<Vec<u8>, FftError> {
+    if blob.len() != FIELD_ELEMENTS_PER_BLOB {
+        return Err(FftError::InvalidBlobSize(blob.len()));
+    }
+    Ok(blob.iter().flat_map(|x| to_bytes(x, BYTES_PER_FIELD_ELEMENT)).collect())
+}
+
 /// Performs the recursive Fast Fourier Transform (FFT) on the input coefficient vector `coeffs`
 /// using the provided group elements `group` and modulus `prime`.
 ///