Merge pull request #128 from rrbutani/pow

Add some tests for pow

Author: alexcrichton

src/math/pow.rs

@@ -408,3 +408,227 @@ pub fn pow(x: f64, y: f64) -> f64 {
 
     return s * z;
 }
+
+#[cfg(test)]
+mod tests {
+    extern crate core;
+
+    use self::core::f64::consts::{E, PI};
+    use self::core::f64::{EPSILON, INFINITY, MAX, MIN, MIN_POSITIVE, NAN, NEG_INFINITY};
+    use super::pow;
+
+    const POS_ZERO: &[f64] = &[0.0];
+    const NEG_ZERO: &[f64] = &[-0.0];
+    const POS_ONE: &[f64] = &[1.0];
+    const NEG_ONE: &[f64] = &[-1.0];
+    const POS_FLOATS: &[f64] = &[99.0 / 70.0, E, PI];
+    const NEG_FLOATS: &[f64] = &[-99.0 / 70.0, -E, -PI];
+    const POS_SMALL_FLOATS: &[f64] = &[(1.0 / 2.0), MIN_POSITIVE, EPSILON];
+    const NEG_SMALL_FLOATS: &[f64] = &[-(1.0 / 2.0), -MIN_POSITIVE, -EPSILON];
+    const POS_EVENS: &[f64] = &[2.0, 6.0, 8.0, 10.0, 22.0, 100.0, MAX];
+    const NEG_EVENS: &[f64] = &[MIN, -100.0, -22.0, -10.0, -8.0, -6.0, -2.0];
+    const POS_ODDS: &[f64] = &[3.0, 7.0];
+    const NEG_ODDS: &[f64] = &[-7.0, -3.0];
+    const NANS: &[f64] = &[NAN];
+    const POS_INF: &[f64] = &[INFINITY];
+    const NEG_INF: &[f64] = &[NEG_INFINITY];
+
+    const ALL: &[&[f64]] = &[
+        POS_ZERO,
+        NEG_ZERO,
+        NANS,
+        NEG_SMALL_FLOATS,
+        POS_SMALL_FLOATS,
+        NEG_FLOATS,
+        POS_FLOATS,
+        NEG_EVENS,
+        POS_EVENS,
+        NEG_ODDS,
+        POS_ODDS,
+        NEG_INF,
+        POS_INF,
+        NEG_ONE,
+        POS_ONE,
+    ];
+    const POS: &[&[f64]] = &[POS_ZERO, POS_ODDS, POS_ONE, POS_FLOATS, POS_EVENS, POS_INF];
+    const NEG: &[&[f64]] = &[NEG_ZERO, NEG_ODDS, NEG_ONE, NEG_FLOATS, NEG_EVENS, NEG_INF];
+
+    fn pow_test(base: f64, exponent: f64, expected: f64) {
+        let res = pow(base, exponent);
+        assert!(
+            if expected.is_nan() {
+                res.is_nan()
+            } else {
+                pow(base, exponent) == expected
+            },
+            "{} ** {} was {} instead of {}",
+            base,
+            exponent,
+            res,
+            expected
+        );
+    }
+
+    fn test_sets_as_base(sets: &[&[f64]], exponent: f64, expected: f64) {
+        sets.iter()
+            .for_each(|s| s.iter().for_each(|val| pow_test(*val, exponent, expected)));
+    }
+
+    fn test_sets_as_exponent(base: f64, sets: &[&[f64]], expected: f64) {
+        sets.iter()
+            .for_each(|s| s.iter().for_each(|val| pow_test(base, *val, expected)));
+    }
+
+    fn test_sets(sets: &[&[f64]], computed: &Fn(f64) -> f64, expected: &Fn(f64) -> f64) {
+        sets.iter().for_each(|s| {
+            s.iter().for_each(|val| {
+                let exp = expected(*val);
+                let res = computed(*val);
+
+                assert!(
+                    if exp.is_nan() {
+                        res.is_nan()
+                    } else {
+                        exp == res
+                    },
+                    "test for {} was {} instead of {}",
+                    val,
+                    res,
+                    exp
+                );
+            })
+        });
+    }
+
+    #[test]
+    fn zero_as_exponent() {
+        test_sets_as_base(ALL, 0.0, 1.0);
+        test_sets_as_base(ALL, -0.0, 1.0);
+    }
+
+    #[test]
+    fn one_as_base() {
+        test_sets_as_exponent(1.0, ALL, 1.0);
+    }
+
+    #[test]
+    fn nan_inputs() {
+        // NAN as the base:
+        // (NAN ^ anything *but 0* should be NAN)
+        test_sets_as_exponent(NAN, &ALL[2..], NAN);
+
+        // NAN as the exponent:
+        // (anything *but 1* ^ NAN should be NAN)
+        test_sets_as_base(&ALL[..(ALL.len() - 2)], NAN, NAN);
+    }
+
+    #[test]
+    fn infinity_as_base() {
+        // Positive Infinity as the base:
+        // (+Infinity ^ positive anything but 0 and NAN should be +Infinity)
+        test_sets_as_exponent(INFINITY, &POS[1..], INFINITY);
+
+        // (+Infinity ^ negative anything except 0 and NAN should be 0.0)
+        test_sets_as_exponent(INFINITY, &NEG[1..], 0.0);
+
+        // Negative Infinity as the base:
+        // (-Infinity ^ positive odd ints should be -Infinity)
+        test_sets_as_exponent(NEG_INFINITY, &[POS_ODDS], NEG_INFINITY);
+
+        // (-Infinity ^ anything but odd ints should be == -0 ^ (-anything))
+        // We can lump in pos/neg odd ints here because they don't seem to
+        // cause panics (div by zero) in release mode (I think).
+        test_sets(ALL, &|v: f64| pow(NEG_INFINITY, v), &|v: f64| pow(-0.0, -v));
+    }
+
+    #[test]
+    fn infinity_as_exponent() {
+        // Positive/Negative base greater than 1:
+        // (pos/neg > 1 ^ Infinity should be Infinity - note this excludes NAN as the base)
+        test_sets_as_base(&ALL[5..(ALL.len() - 2)], INFINITY, INFINITY);
+
+        // (pos/neg > 1 ^ -Infinity should be 0.0)
+        test_sets_as_base(&ALL[5..ALL.len() - 2], NEG_INFINITY, 0.0);
+
+        // Positive/Negative base less than 1:
+        let base_below_one = &[POS_ZERO, NEG_ZERO, NEG_SMALL_FLOATS, POS_SMALL_FLOATS];
+
+        // (pos/neg < 1 ^ Infinity should be 0.0 - this also excludes NAN as the base)
+        test_sets_as_base(base_below_one, INFINITY, 0.0);
+
+        // (pos/neg < 1 ^ -Infinity should be Infinity)
+        test_sets_as_base(base_below_one, NEG_INFINITY, INFINITY);
+
+        // Positive/Negative 1 as the base:
+        // (pos/neg 1 ^ Infinity should be 1)
+        test_sets_as_base(&[NEG_ONE, POS_ONE], INFINITY, 1.0);
+
+        // (pos/neg 1 ^ -Infinity should be 1)
+        test_sets_as_base(&[NEG_ONE, POS_ONE], NEG_INFINITY, 1.0);
+    }
+
+    #[test]
+    fn zero_as_base() {
+        // Positive Zero as the base:
+        // (+0 ^ anything positive but 0 and NAN should be +0)
+        test_sets_as_exponent(0.0, &POS[1..], 0.0);
+
+        // (+0 ^ anything negative but 0 and NAN should be Infinity)
+        // (this should panic because we're dividing by zero)
+        test_sets_as_exponent(0.0, &NEG[1..], INFINITY);
+
+        // Negative Zero as the base:
+        // (-0 ^ anything positive but 0, NAN, and odd ints should be +0)
+        test_sets_as_exponent(-0.0, &POS[3..], 0.0);
+
+        // (-0 ^ anything negative but 0, NAN, and odd ints should be Infinity)
+        // (should panic because of divide by zero)
+        test_sets_as_exponent(-0.0, &NEG[3..], INFINITY);
+
+        // (-0 ^ positive odd ints should be -0)
+        test_sets_as_exponent(-0.0, &[POS_ODDS], -0.0);
+
+        // (-0 ^ negative odd ints should be -Infinity)
+        // (should panic because of divide by zero)
+        test_sets_as_exponent(-0.0, &[NEG_ODDS], NEG_INFINITY);
+    }
+
+    #[test]
+    fn special_cases() {
+        // One as the exponent:
+        // (anything ^ 1 should be anything - i.e. the base)
+        test_sets(ALL, &|v: f64| pow(v, 1.0), &|v: f64| v);
+
+        // Negative One as the exponent:
+        // (anything ^ -1 should be 1/anything)
+        test_sets(ALL, &|v: f64| pow(v, -1.0), &|v: f64| 1.0 / v);
+
+        // Factoring -1 out:
+        // (negative anything ^ integer should be (-1 ^ integer) * (positive anything ^ integer))
+        &[POS_ZERO, NEG_ZERO, POS_ONE, NEG_ONE, POS_EVENS, NEG_EVENS]
+            .iter()
+            .for_each(|int_set| {
+                int_set.iter().for_each(|int| {
+                    test_sets(ALL, &|v: f64| pow(-v, *int), &|v: f64| {
+                        pow(-1.0, *int) * pow(v, *int)
+                    });
+                })
+            });
+
+        // Negative base (imaginary results):
+        // (-anything except 0 and Infinity ^ non-integer should be NAN)
+        &NEG[1..(NEG.len() - 1)].iter().for_each(|set| {
+            set.iter().for_each(|val| {
+                test_sets(&ALL[3..7], &|v: f64| pow(*val, v), &|_| NAN);
+            })
+        });
+    }
+
+    #[test]
+    fn normal_cases() {
+        assert_eq!(pow(2.0, 20.0), (1 << 20) as f64);
+        assert_eq!(pow(-1.0, 9.0), -1.0);
+        assert!(pow(-1.0, 2.2).is_nan());
+        assert!(pow(-1.0, -1.14).is_nan());
+    }
+}