Function syscall_secp256r1_decompress_impl 

pub fn syscall_secp256r1_decompress_impl(
    x_bytes_le: [u8; 32],
    sign_bit: u32,
) -> Result<[u8; 64], ExitCode>

Secp256r1 point decompression.

Input format

• x_bytes_le: x-coordinate as 32 bytes in little-endian
• sign_bit: 0 or 1, indicates which y to recover

Output

Affine point [y || x] in little-endian (64 bytes total, y first).

Validation

Returns ExitCode::MalformedBuiltinParams if:

• sign_bit > 1
• x-coordinate doesn’t correspond to a valid curve point