feat: Add signum (TheAlgorithms#419)

Author: SpiderMath

Diff for: src/math/mod.rs

@@ -31,6 +31,7 @@ mod prime_numbers;
 mod quadratic_residue;
 mod random;
 mod sieve_of_eratosthenes;
+mod signum;
 mod simpson_integration;
 mod square_root;
 mod trial_division;
@@ -76,6 +77,7 @@ pub use self::prime_numbers::prime_numbers;
 pub use self::quadratic_residue::cipolla;
 pub use self::random::PCG32;
 pub use self::sieve_of_eratosthenes::sieve_of_eratosthenes;
+pub use self::signum::signum;
 pub use self::simpson_integration::simpson_integration;
 pub use self::square_root::{fast_inv_sqrt, square_root};
 pub use self::trial_division::trial_division;

Diff for: src/math/signum.rs

@@ -0,0 +1,36 @@
+/// Signum function is a mathematical function that extracts
+/// the sign of a real number. It is also known as the sign function,
+/// and it is an odd piecewise function.
+/// If a number is negative, i.e. it is less than zero, then sgn(x) = -1
+/// If a number is zero, then sgn(0) = 0
+/// If a number is positive, i.e. it is greater than zero, then sgn(x) = 1
+
+pub fn signum(number: f64) -> i8 {
+    if number == 0.0 {
+        return 0;
+    } else if number > 0.0 {
+        return 1;
+    }
+
+    -1
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn positive_integer() {
+        assert_eq!(signum(15.0), 1);
+    }
+
+    #[test]
+    fn negative_integer() {
+        assert_eq!(signum(-30.0), -1);
+    }
+
+    #[test]
+    fn zero() {
+        assert_eq!(signum(0.0), 0);
+    }
+}