Merge pull request #30 from arkpar/bitscan

Implemented trailing_zeros and leading_zeros

Cargo.toml

@@ -4,7 +4,7 @@ homepage = "http://parity.io"
 repository = "https://github.com/ethcore/bigint"
 license = "MIT/Apache-2.0"
 name = "bigint"
-version = "4.1.2"
+version = "4.1.3"
 authors = ["Parity Technologies <admin@parity.io>"]
 build = "build.rs"
 

src/uint.rs

@@ -622,6 +622,36 @@ macro_rules! construct_uint {
 				arr[index / 64] & (1 << (index % 64)) != 0
 			}
 
+			/// Returns the number of leading zeros in the binary representation of self.
+			pub fn leading_zeros(&self) -> u32 {
+				let mut r = 0;
+				for i in 0..$n_words {
+					let w = self.0[$n_words - i - 1];
+					if w == 0 {
+						r += 64;
+					} else {
+						r += w.leading_zeros();
+						break;
+					}
+				}
+				r
+			}
+
+			/// Returns the number of leading zeros in the binary representation of self.
+			pub fn trailing_zeros(&self) -> u32 {
+				let mut r = 0;
+				for i in 0..$n_words {
+					let w = self.0[i];
+					if w == 0 {
+						r += 64;
+					} else {
+						r += w.trailing_zeros();
+						break;
+					}
+				}
+				r
+			}
+
 			/// Return specific byte.
 			///
 			/// # Panics
@@ -2484,4 +2514,20 @@ mod tests {
 
 		assert_eq!(U256::from(1), number);
 	}
+
+	#[test]
+	fn leading_zeros() {
+		assert_eq!(U256::from("000000000000000000000001adbdd6bd6ff027485484b97f8a6a4c7129756dd1").leading_zeros(), 95);
+		assert_eq!(U256::from("f00000000000000000000001adbdd6bd6ff027485484b97f8a6a4c7129756dd1").leading_zeros(), 0);
+		assert_eq!(U256::from("0000000000000000000000000000000000000000000000000000000000000001").leading_zeros(), 255);
+		assert_eq!(U256::from("0000000000000000000000000000000000000000000000000000000000000000").leading_zeros(), 256);
+	}
+
+	#[test]
+	fn trailing_zeros() {
+		assert_eq!(U256::from("1adbdd6bd6ff027485484b97f8a6a4c7129756dd100000000000000000000000").trailing_zeros(), 92);
+		assert_eq!(U256::from("1adbdd6bd6ff027485484b97f8a6a4c7129756dd10000000000000000000000f").trailing_zeros(), 0);
+		assert_eq!(U256::from("8000000000000000000000000000000000000000000000000000000000000000").trailing_zeros(), 255);
+		assert_eq!(U256::from("0000000000000000000000000000000000000000000000000000000000000000").trailing_zeros(), 256);
+	}
  }