✨ feat: Add sign function.

src/compare/sign.js

@@ -0,0 +1,7 @@
+/**
+ * Computes the sign of the input number.
+ *
+ * @param {number} v - The number to compute the sign of.
+ * @return {number} -1 if v < 0, 1 if v > 0, 0 otherwise.
+ */
+export const sign = (v) => (v < 0 ? -1 : v > 0 ? 1 : 0);

src/index.js

@@ -30,6 +30,7 @@ export {shu} from './arithmetic/shu.js';
 export {sub} from './arithmetic/sub.js';
 export {decreasing} from './compare/decreasing.js';
 export {increasing} from './compare/increasing.js';
+export {sign} from './compare/sign.js';
 export {$0} from './constants/$0.js';
 export {$1} from './constants/$1.js';
 export {$2} from './constants/$2.js';

test/src/compare/sign.js

@@ -0,0 +1,29 @@
+import test from 'ava';
+
+import {sign} from '../../../src/index.js';
+
+const macro = (t, input, output) => {
+	t.is(sign(input), output);
+};
+
+macro.title = (title, input, output) => title ?? `sign(${input}) = ${output}`;
+
+test(macro, 0, 0);
+
+test(macro, -1, -1);
+test(macro, 1, 1);
+
+test(macro, -999, -1);
+test(macro, 999, 1);
+
+test(macro, Number.MIN_SAFE_INTEGER, -1);
+test(macro, Number.MAX_SAFE_INTEGER, 1);
+
+test(macro, Number.NEGATIVE_INFINITY, -1);
+test(macro, Number.POSITIVE_INFINITY, 1);
+
+test(macro, Number.MIN_VALUE, 1);
+test(macro, Number.MAX_VALUE, 1);
+
+test(macro, Number.EPSILON, 1);
+test(macro, Number.NaN, 0);