---

yaml
---
r: 97244
b: refs/heads/dist-snap
c: a1d3cc5
h: refs/heads/master
v: v3

Author: bors

[refs]

@@ -6,7 +6,7 @@ refs/heads/try: c274a6888410ce3e357e014568b43310ed787d36
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c
-refs/heads/dist-snap: 856222987d08289ef03a06ebf7b59087e226e9e9
+refs/heads/dist-snap: a1d3cc53860b1e2377e489333e1f41dec6132b10
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0

branches/dist-snap/src/libextra/num/rational.rs

@@ -14,7 +14,7 @@
 use std::cmp;
 use std::from_str::FromStr;
 use std::num::{Zero,One,ToStrRadix,FromStrRadix,Round};
-use super::bigint::BigInt;
+use super::bigint::{BigInt, BigUint, Sign, Plus, Minus};
 
 /// Represents the ratio between 2 numbers.
 #[deriving(Clone)]
@@ -107,6 +107,27 @@ impl<T: Clone + Integer + Ord>
     }
 }
 
+impl Ratio<BigInt> {
+    /// Converts a float into a rational number
+    pub fn from_float<T: Float>(f: T) -> Option<BigRational> {
+        if !f.is_finite() {
+            return None;
+        }
+        let (mantissa, exponent, sign) = f.integer_decode();
+        let bigint_sign: Sign = if sign == 1 { Plus } else { Minus };
+        if exponent < 0 {
+            let one: BigInt = One::one();
+            let denom: BigInt = one << ((-exponent) as uint);
+            let numer: BigUint = FromPrimitive::from_u64(mantissa).unwrap();
+            Some(Ratio::new(BigInt::from_biguint(bigint_sign, numer), denom))
+        } else {
+            let mut numer: BigUint = FromPrimitive::from_u64(mantissa).unwrap();
+            numer = numer << (exponent as uint);
+            Some(Ratio::from_integer(BigInt::from_biguint(bigint_sign, numer)))
+        }
+    }
+}
+
 /* Comparisons */
 
 // comparing a/b and c/d is the same as comparing a*d and b*c, so we
@@ -621,4 +642,42 @@ mod test {
             test(s);
         }
     }
+
+    #[test]
+    fn test_from_float() {
+        fn test<T: Float>(given: T, (numer, denom): (&str, &str)) {
+            let ratio: BigRational = Ratio::from_float(given).unwrap();
+            assert_eq!(ratio, Ratio::new(
+                FromStr::from_str(numer).unwrap(),
+                FromStr::from_str(denom).unwrap()));
+        }
+
+        // f32
+        test(3.14159265359f32, ("13176795", "4194304"));
+        test(2f32.pow(&100.), ("1267650600228229401496703205376", "1"));
+        test(-2f32.pow(&100.), ("-1267650600228229401496703205376", "1"));
+        test(1.0 / 2f32.pow(&100.), ("1", "1267650600228229401496703205376"));
+        test(684729.48391f32, ("1369459", "2"));
+        test(-8573.5918555f32, ("-4389679", "512"));
+
+        // f64
+        test(3.14159265359f64, ("3537118876014453", "1125899906842624"));
+        test(2f64.pow(&100.), ("1267650600228229401496703205376", "1"));
+        test(-2f64.pow(&100.), ("-1267650600228229401496703205376", "1"));
+        test(684729.48391f64, ("367611342500051", "536870912"));
+        test(-8573.5918555, ("-4713381968463931", "549755813888"));
+        test(1.0 / 2f64.pow(&100.), ("1", "1267650600228229401496703205376"));
+    }
+
+    #[test]
+    fn test_from_float_fail() {
+        use std::{f32, f64};
+
+        assert_eq!(Ratio::from_float(f32::NAN), None);
+        assert_eq!(Ratio::from_float(f32::INFINITY), None);
+        assert_eq!(Ratio::from_float(f32::NEG_INFINITY), None);
+        assert_eq!(Ratio::from_float(f64::NAN), None);
+        assert_eq!(Ratio::from_float(f64::INFINITY), None);
+        assert_eq!(Ratio::from_float(f64::NEG_INFINITY), None);
+    }
 }