Add support for the bignum system library

Cargo.toml

@@ -14,3 +14,4 @@ wee_alloc = "0.4.4"
 default = [ "std" ]
 std = []
 debug = []
+bignum = []

src/bignum.rs

@@ -0,0 +1,39 @@
+//! The bignum system library.
+
+use super::*;
+
+pub mod native {
+    extern "C" {
+        pub fn bignum_mul256(a: *const u32, b: *const u32, ret: *mut u32);
+        pub fn bignum_umulmod256(a: *const u32, b: *const u32, modulo: *const u32, ret: *mut u32);
+    }
+}
+
+pub fn mul256(a: &Uint256, b: &Uint256) -> Uint256 {
+    let mut ret = Uint256::default();
+
+    unsafe {
+        native::bignum_mul256(
+            a.bytes.as_ptr() as *const u32,
+            b.bytes.as_ptr() as *const u32,
+            ret.bytes.as_mut_ptr() as *const u32,
+        )
+    }
+
+    ret
+}
+
+pub fn umulmod256(a: &Uint256, b: &Uint256, modulo: &Uint256) -> Uint256 {
+    let mut ret = Uint256::default();
+
+    unsafe {
+        native::bignum_mul256(
+            a.bytes.as_ptr() as *const u32,
+            b.bytes.as_ptr() as *const u32,
+            modulo.bytes.as_ptr() as *const u32,
+            ret.bytes.as_mut_ptr() as *const u32,
+        )
+    }
+
+    ret
+}

src/lib.rs

@@ -31,6 +31,9 @@ mod utils;
 #[cfg(feature = "debug")]
 pub mod debug;
 
+#[cfg(feature = "bignum")]
+pub mod bignum;
+
 #[cfg(not(feature = "std"))]
 pub mod convert;