---

yaml
---
r: 144946
b: refs/heads/try2
c: 54368af
h: refs/heads/master
v: v3

Author: dcrewi

[refs]

@@ -5,7 +5,7 @@ refs/heads/snap-stage3: 78a7676898d9f80ab540c6df5d4c9ce35bb50463
 refs/heads/try: 519addf6277dbafccbb4159db4b710c37eaa2ec5
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
-refs/heads/try2: 43399529343bff6fc4ee5643b1f8f642b151ffff
+refs/heads/try2: 54368afc03054937e7f5a3b7a9b8cf9c8e85d962
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/try2/src/libextra/num/bigint.rs

@@ -526,7 +526,7 @@ trait RandBigUInt {
     fn gen_biguint(&mut self, bit_size: uint) -> BigUint;
 }
 
-impl<R: RngUtil> RandBigUInt for R {
+impl<R: Rng> RandBigUInt for R {
     /// Generate a random BigUint of the given bit size.
     fn gen_biguint(&mut self, bit_size: uint) -> BigUint {
         let (digits, rem) = bit_size.div_rem(&BigDigit::bits);
@@ -1078,13 +1078,27 @@ trait RandBigInt {
     fn gen_bigint(&mut self, bit_size: uint) -> BigInt;
 }
 
-impl<R: RngUtil> RandBigInt for R {
+impl<R: Rng> RandBigInt for R {
     /// Generate a random BigUint of the given bit size.
     fn gen_bigint(&mut self, bit_size: uint) -> BigInt {
+        // Generate a random BigUint...
         let biguint = self.gen_biguint(bit_size);
-        let sign = if biguint.is_zero() { Zero }
-            else if self.gen() { Plus }
-            else { Minus };
+        // ...and then randomly assign it a Sign...
+        let sign = if biguint.is_zero() {
+            // ...except that if the BigUint is zero, we need to try
+            // again with probability 0.5. This is because otherwise,
+            // the probability of generating a zero BigInt would be
+            // double that of any other number.
+            if self.gen() {
+                return self.gen_bigint(bit_size);
+            } else {
+                Zero
+            }
+        } else if self.gen() {
+            Plus
+        } else {
+            Minus
+        };
         return BigInt::from_biguint(sign, biguint);
     }
 }
@@ -1620,7 +1634,8 @@ mod biguint_tests {
     #[test]
     fn test_rand() {
         let mut rng = task_rng();
-        let n: BigUint = rng.gen_biguint(137);
+        let _n: BigUint = rng.gen_biguint(137);
+        assert!(rng.gen_biguint(0).is_zero());
     }
 }
 
@@ -2056,7 +2071,7 @@ mod bigint_tests {
     #[test]
     fn test_rand() {
         let mut rng = task_rng();
-        let n: BigInt = rng.gen_bigint(137);
+        let _n: BigInt = rng.gen_bigint(137);
         assert!(rng.gen_bigint(0).is_zero());
     }
 }