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)]
}
}
+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
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);
+ }
}