Add ldexp and frexp functions

Author: brendanzab

src/libcore/num/f32.rs

@@ -10,6 +10,7 @@
 
 //! Operations and constants for `f32`
 
+use libc::c_int;
 use num::{Zero, One, strconv};
 use num::{FPCategory, FPNaN, FPInfinite , FPZero, FPSubnormal, FPNormal};
 use prelude::*;
@@ -672,6 +673,25 @@ impl Float for f32 {
     #[inline(always)]
     fn max_10_exp() -> int { 38 }
 
+    /// Constructs a floating point number by multiplying `x` by 2 raised to the power of `exp`
+    #[inline(always)]
+    fn ldexp(x: f32, exp: int) -> f32 {
+        ldexp(x, exp as c_int)
+    }
+
+    ///
+    /// Breaks the number into a normalized fraction and a base-2 exponent, satisfying:
+    ///
+    /// - `self = x * pow(2, exp)`
+    /// - `0.5 <= abs(x) < 1.0`
+    ///
+    #[inline(always)]
+    fn frexp(&self) -> (f32, int) {
+        let mut exp = 0;
+        let x = frexp(*self, &mut exp);
+        (x, exp as int)
+    }
+
     ///
     /// Returns the exponential of the number, minus `1`, in a way that is accurate
     /// even if the number is close to zero
@@ -1180,4 +1200,44 @@ mod tests {
         assert_eq!(1e-37f32.classify(), FPNormal);
         assert_eq!(1e-38f32.classify(), FPSubnormal);
     }
+
+    #[test]
+    fn test_ldexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: f32 = from_str_hex("1p-123").unwrap();
+        let f2: f32 = from_str_hex("1p-111").unwrap();
+        assert_eq!(Float::ldexp(1f32, -123), f1);
+        assert_eq!(Float::ldexp(1f32, -111), f2);
+
+        assert_eq!(Float::ldexp(0f32, -123), 0f32);
+        assert_eq!(Float::ldexp(-0f32, -123), -0f32);
+        assert_eq!(Float::ldexp(Float::infinity::<f32>(), -123),
+                   Float::infinity::<f32>());
+        assert_eq!(Float::ldexp(Float::neg_infinity::<f32>(), -123),
+                   Float::neg_infinity::<f32>());
+        assert!(Float::ldexp(Float::NaN::<f32>(), -123).is_NaN());
+    }
+
+    #[test]
+    fn test_frexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: f32 = from_str_hex("1p-123").unwrap();
+        let f2: f32 = from_str_hex("1p-111").unwrap();
+        let (x1, exp1) = f1.frexp();
+        let (x2, exp2) = f2.frexp();
+        assert_eq!((x1, exp1), (0.5f32, -122));
+        assert_eq!((x2, exp2), (0.5f32, -110));
+        assert_eq!(Float::ldexp(x1, exp1), f1);
+        assert_eq!(Float::ldexp(x2, exp2), f2);
+
+        assert_eq!(0f32.frexp(), (0f32, 0));
+        assert_eq!((-0f32).frexp(), (-0f32, 0));
+        assert_eq!(match Float::infinity::<f32>().frexp() { (x, _) => x },
+                   Float::infinity::<f32>())
+        assert_eq!(match Float::neg_infinity::<f32>().frexp() { (x, _) => x },
+                   Float::neg_infinity::<f32>())
+        assert!(match Float::NaN::<f32>().frexp() { (x, _) => x.is_NaN() })
+    }
 }

src/libcore/num/f64.rs

@@ -715,6 +715,25 @@ impl Float for f64 {
     #[inline(always)]
     fn max_10_exp() -> int { 308 }
 
+    /// Constructs a floating point number by multiplying `x` by 2 raised to the power of `exp`
+    #[inline(always)]
+    fn ldexp(x: f64, exp: int) -> f64 {
+        ldexp(x, exp as c_int)
+    }
+
+    ///
+    /// Breaks the number into a normalized fraction and a base-2 exponent, satisfying:
+    ///
+    /// - `self = x * pow(2, exp)`
+    /// - `0.5 <= abs(x) < 1.0`
+    ///
+    #[inline(always)]
+    fn frexp(&self) -> (f64, int) {
+        let mut exp = 0;
+        let x = frexp(*self, &mut exp);
+        (x, exp as int)
+    }
+
     ///
     /// Returns the exponential of the number, minus `1`, in a way that is accurate
     /// even if the number is close to zero
@@ -1226,4 +1245,44 @@ mod tests {
         assert_eq!(1e-307f64.classify(), FPNormal);
         assert_eq!(1e-308f64.classify(), FPSubnormal);
     }
+
+    #[test]
+    fn test_ldexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: f64 = from_str_hex("1p-123").unwrap();
+        let f2: f64 = from_str_hex("1p-111").unwrap();
+        assert_eq!(Float::ldexp(1f64, -123), f1);
+        assert_eq!(Float::ldexp(1f64, -111), f2);
+
+        assert_eq!(Float::ldexp(0f64, -123), 0f64);
+        assert_eq!(Float::ldexp(-0f64, -123), -0f64);
+        assert_eq!(Float::ldexp(Float::infinity::<f64>(), -123),
+                   Float::infinity::<f64>());
+        assert_eq!(Float::ldexp(Float::neg_infinity::<f64>(), -123),
+                   Float::neg_infinity::<f64>());
+        assert!(Float::ldexp(Float::NaN::<f64>(), -123).is_NaN());
+    }
+
+    #[test]
+    fn test_frexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: f64 = from_str_hex("1p-123").unwrap();
+        let f2: f64 = from_str_hex("1p-111").unwrap();
+        let (x1, exp1) = f1.frexp();
+        let (x2, exp2) = f2.frexp();
+        assert_eq!((x1, exp1), (0.5f64, -122));
+        assert_eq!((x2, exp2), (0.5f64, -110));
+        assert_eq!(Float::ldexp(x1, exp1), f1);
+        assert_eq!(Float::ldexp(x2, exp2), f2);
+
+        assert_eq!(0f64.frexp(), (0f64, 0));
+        assert_eq!((-0f64).frexp(), (-0f64, 0));
+        assert_eq!(match Float::infinity::<f64>().frexp() { (x, _) => x },
+                   Float::infinity::<f64>())
+        assert_eq!(match Float::neg_infinity::<f64>().frexp() { (x, _) => x },
+                   Float::neg_infinity::<f64>())
+        assert!(match Float::NaN::<f64>().frexp() { (x, _) => x.is_NaN() })
+    }
 }

src/libcore/num/float.rs

@@ -881,6 +881,25 @@ impl Float for float {
     #[inline(always)]
     fn max_10_exp() -> int { Float::max_10_exp::<f64>() }
 
+    /// Constructs a floating point number by multiplying `x` by 2 raised to the power of `exp`
+    #[inline(always)]
+    fn ldexp(x: float, exp: int) -> float {
+        Float::ldexp(x as f64, exp) as float
+    }
+
+    ///
+    /// Breaks the number into a normalized fraction and a base-2 exponent, satisfying:
+    ///
+    /// - `self = x * pow(2, exp)`
+    /// - `0.5 <= abs(x) < 1.0`
+    ///
+    #[inline(always)]
+    fn frexp(&self) -> (float, int) {
+        match (*self as f64).frexp() {
+            (x, exp) => (x as float, exp)
+        }
+    }
+
     ///
     /// Returns the exponential of the number, minus `1`, in a way that is accurate
     /// even if the number is close to zero
@@ -895,7 +914,9 @@ impl Float for float {
     /// than if the operations were performed separately
     ///
     #[inline(always)]
-    fn ln_1p(&self) -> float { (*self as f64).ln_1p() as float }
+    fn ln_1p(&self) -> float {
+        (*self as f64).ln_1p() as float
+    }
 
     ///
     /// Fused multiply-add. Computes `(self * a) + b` with only one rounding error. This
@@ -1174,6 +1195,46 @@ mod tests {
         assert_eq!(1e-308f.classify(), FPSubnormal);
     }
 
+    #[test]
+    fn test_ldexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: float = from_str_hex("1p-123").unwrap();
+        let f2: float = from_str_hex("1p-111").unwrap();
+        assert_eq!(Float::ldexp(1f, -123), f1);
+        assert_eq!(Float::ldexp(1f, -111), f2);
+
+        assert_eq!(Float::ldexp(0f, -123), 0f);
+        assert_eq!(Float::ldexp(-0f, -123), -0f);
+        assert_eq!(Float::ldexp(Float::infinity::<float>(), -123),
+                   Float::infinity::<float>());
+        assert_eq!(Float::ldexp(Float::neg_infinity::<float>(), -123),
+                   Float::neg_infinity::<float>());
+        assert!(Float::ldexp(Float::NaN::<float>(), -123).is_NaN());
+    }
+
+    #[test]
+    fn test_frexp() {
+        // We have to use from_str until base-2 exponents
+        // are supported in floating-point literals
+        let f1: float = from_str_hex("1p-123").unwrap();
+        let f2: float = from_str_hex("1p-111").unwrap();
+        let (x1, exp1) = f1.frexp();
+        let (x2, exp2) = f2.frexp();
+        assert_eq!((x1, exp1), (0.5f, -122));
+        assert_eq!((x2, exp2), (0.5f, -110));
+        assert_eq!(Float::ldexp(x1, exp1), f1);
+        assert_eq!(Float::ldexp(x2, exp2), f2);
+
+        assert_eq!(0f.frexp(), (0f, 0));
+        assert_eq!((-0f).frexp(), (-0f, 0));
+        assert_eq!(match Float::infinity::<float>().frexp() { (x, _) => x },
+                   Float::infinity::<float>())
+        assert_eq!(match Float::neg_infinity::<float>().frexp() { (x, _) => x },
+                   Float::neg_infinity::<float>())
+        assert!(match Float::NaN::<float>().frexp() { (x, _) => x.is_NaN() })
+    }
+
     #[test]
     pub fn test_to_str_exact_do_decimal() {
         let s = to_str_exact(5.0, 4u);

src/libcore/num/num.rs

@@ -284,6 +284,9 @@ pub trait Float: Real
     fn min_10_exp() -> int;
     fn max_10_exp() -> int;
 
+    fn ldexp(x: Self, exp: int) -> Self;
+    fn frexp(&self) -> (Self, int);
+
     fn exp_m1(&self) -> Self;
     fn ln_1p(&self) -> Self;
     fn mul_add(&self, a: Self, b: Self) -> Self;