Merge pull request #436 from LNP-BP/feat-u256u8

Big integers (Uint*) from byte slice array with `from_be_bytes`

fuzz/fuzz_targets/uint128_fuzz.rs

@@ -1,5 +1,6 @@
 extern crate bitcoin;
 use std::str::FromStr;
+use std::convert::Into;
 
 fn do_test(data: &[u8]) {
     macro_rules! read_ints {
@@ -11,6 +12,12 @@ fn do_test(data: &[u8]) {
             }
             // Note BE:
             let uint128 = bitcoin::util::uint::Uint128::from(&[native as u64, (native >> 8*8) as u64][..]);
+
+            // Checking two conversion methods against each other
+            let mut slice = [0u8; 16];
+            slice.copy_from_slice(&data[$start..$start + 16]);
+            assert_eq!(uint128, bitcoin::util::uint::Uint128::from_be_bytes(slice));
+
             (native, uint128)
         } }
     }

src/util/endian.rs

@@ -52,6 +52,7 @@ macro_rules! define_le_to_array {
 }
 
 define_slice_to_be!(slice_to_u32_be, u32);
+define_slice_to_be!(slice_to_u64_be, u64);
 define_be_to_array!(u32_to_array_be, u32, 4);
 define_slice_to_le!(slice_to_u16_le, u16);
 define_slice_to_le!(slice_to_u32_le, u32);
@@ -105,6 +106,7 @@ mod tests {
     #[test]
     fn endianness_test() {
         assert_eq!(slice_to_u32_be(&[0xde, 0xad, 0xbe, 0xef]), 0xdeadbeef);
+        assert_eq!(slice_to_u64_be(&[0xde, 0xad, 0xbe, 0xef, 0x1b, 0xad, 0xca, 0xfe]), 0xdeadbeef1badcafe);
         assert_eq!(u32_to_array_be(0xdeadbeef), [0xde, 0xad, 0xbe, 0xef]);
 
         assert_eq!(slice_to_u16_le(&[0xad, 0xde]), 0xdead);

src/util/uint.rs

@@ -73,6 +73,7 @@ macro_rules! construct_uint {
             }
 
             /// Create an object from a given unsigned 64-bit integer
+            #[inline]
             pub fn from_u64(init: u64) -> Option<$name> {
                 let mut ret = [0; $n_words];
                 ret[0] = init;
@@ -80,11 +81,24 @@ macro_rules! construct_uint {
             }
 
             /// Create an object from a given signed 64-bit integer
+            #[inline]
             pub fn from_i64(init: i64) -> Option<$name> {
                 assert!(init >= 0);
                 $name::from_u64(init as u64)
             }
 
+            /// Creates big integer value from a byte slice array using
+            /// big-endian encoding
+            pub fn from_be_bytes(bytes: [u8; $n_words * 8]) -> $name {
+                use super::endian::slice_to_u64_be;
+                let mut slice = [0u64; $n_words];
+                slice.iter_mut()
+                    .rev()
+                    .zip(bytes.chunks(8))
+                    .for_each(|(word, bytes)| *word = slice_to_u64_be(bytes));
+                $name(slice)
+            }
+
             // divmod like operation, returns (quotient, remainder)
             #[inline]
             fn div_rem(self, other: Self) -> (Self, Self) {
@@ -409,7 +423,7 @@ impl Uint256 {
 #[cfg(test)]
 mod tests {
     use consensus::{deserialize, serialize};
-    use util::uint::Uint256;
+    use util::uint::{Uint256, Uint128};
     use util::BitArray;
 
     #[test]
@@ -467,6 +481,16 @@ mod tests {
         assert!(small <= small);
     }
 
+    #[test]
+    pub fn uint_from_be_bytes() {
+        assert_eq!(Uint128::from_be_bytes([0x1b, 0xad, 0xca, 0xfe, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xaf, 0xba, 0xbe, 0x2b, 0xed, 0xfe, 0xed]),
+                   Uint128([0xdeafbabe2bedfeed, 0x1badcafedeadbeef]));
+
+        assert_eq!(Uint256::from_be_bytes([0x1b, 0xad, 0xca, 0xfe, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xaf, 0xba, 0xbe, 0x2b, 0xed, 0xfe, 0xed,
+                                           0xba, 0xad, 0xf0, 0x0d, 0xde, 0xfa, 0xce, 0xda, 0x11, 0xfe, 0xd2, 0xba, 0xd1, 0xc0, 0xff, 0xe0]),
+                   Uint256([0x11fed2bad1c0ffe0, 0xbaadf00ddefaceda, 0xdeafbabe2bedfeed, 0x1badcafedeadbeef]));
+    }
+
     #[test]
     pub fn uint256_arithmetic_test() {
         let init = Uint256::from_u64(0xDEADBEEFDEADBEEF).unwrap();