feat: add lerp function (#86)

benchmarks/number/lerp.bench.ts

@@ -0,0 +1,8 @@
+import * as _ from 'radashi'
+import { bench } from 'vitest'
+
+describe('lerp', () => {
+  bench('with valid input', () => {
+    _.lerp(0, 10, 0.5)
+  })
+})

docs/number/lerp.mdx

@@ -0,0 +1,22 @@
+---
+title: lerp
+description: Smoothly transitions between two values based on a factor
+---
+
+## Basic usage
+
+The `lerp` function is used to linearly interpolate between two numbers based on a specified amount. This function is particularly useful in animations, graphics, and games for smooth transitions.
+
+```ts
+import * as _ from 'radashi'
+
+_.lerp(0, 10, 0.5) // => 5
+_.lerp(5, 15, 0.2) // => 7
+_.lerp(-10, 10, 0.75) // => 5
+```
+
+## Etymology
+
+The name `lerp` is short for "linear interpolation". It's a term from computer graphics that means "interpolate linearly between two values".
+
+For more information, check out the [Wikipedia article](https://en.wikipedia.org/wiki/Linear_interpolation) on linear interpolation.

src/mod.ts

@@ -55,6 +55,7 @@ export * from './curry/proxied.ts'
 export * from './curry/throttle.ts'
 
 export * from './number/inRange.ts'
+export * from './number/lerp.ts'
 export * from './number/round.ts'
 export * from './number/toFloat.ts'
 export * from './number/toInt.ts'

src/number/lerp.ts

@@ -0,0 +1,12 @@
+/**
+ * Linearly interpolates between two numbers.
+ *
+ * ```
+ * lerp(0, 10, 0.5) // => 5
+ * lerp(5, 15, 0.2) // => 7
+ * lerp(-10, 10, 0.75) // => 5
+ * ```
+ */
+export function lerp(from: number, to: number, amount: number): number {
+  return from + (to - from) * amount
+}

tests/number/lerp.test.ts

@@ -0,0 +1,22 @@
+import * as _ from 'radashi'
+
+describe('lerp', () => {
+  test('linearly interpolate between two numbers', () => {
+    expect(_.lerp(0, 10, 0.5)).toBe(5)
+    expect(_.lerp(5, 15, 0.2)).toBe(7)
+    expect(_.lerp(-10, 10, 0.75)).toBe(5)
+  })
+  test('edge cases', () => {
+    expect(_.lerp(0, 10, 0)).toBe(0)
+    expect(_.lerp(0, 10, 1)).toBe(10)
+    expect(_.lerp(5, 5, 0.5)).toBe(5)
+  })
+  test('negative numbers', () => {
+    expect(_.lerp(-5, 5, 0.5)).toBe(0)
+    expect(_.lerp(-10, -5, 0.5)).toBe(-7.5)
+  })
+  test('decimal results', () => {
+    expect(_.lerp(0, 1, 0.3)).toBeCloseTo(0.3, 5)
+    expect(_.lerp(1, 2, 0.75)).toBeCloseTo(1.75, 5)
+  })
+})