Merge pull request #13 from Rudxain/abs_ratio

add abs-ratio

wiki/Absolute_ratio.md

@@ -0,0 +1,37 @@
+# Absolute ratio
+Defined as the [quotient](https://en.wikipedia.org/wiki/Quotient) between the maximum and minimum [absolute-values](https://en.wikipedia.org/wiki/Absolute_value) of both input arguments.
+
+## Applications
+It can be used to guarantee that integer division is always greater than 0, which "preserves" the information of the operands.
+
+## Implementation
+[PFP](https://en.wikipedia.org/wiki/Pure_functional_programming)-style code in both Python and TypeScript, respectively:
+```py
+from typing import Final, Callable
+# there's `TypeVar` but `//` forces us to `def` 2 APIs
+
+fabs_ratio: Final[Callable[[float, float], float]] = lambda x, y, /: (
+	lambda x, y: max(x, y) / min(x, y)
+)(abs(x), abs(y))
+
+iabs_ratio: Final[Callable[[int, int], int]] = lambda x, y, /: (
+	lambda x, y: max(x, y) // min(x, y)
+)(abs(x), abs(y))
+```
+```ts
+type numeric = number | bigint
+
+const
+	max = <T extends numeric,>(x: T, y: T) =>
+		x < y ? y : x,
+	min = <T extends numeric,>(x: T, y: T) =>
+		x > y ? y : x,
+	abs = <T extends numeric,>(x: T) =>
+		x < 0 ? -x as T : x
+
+const abs_ratio = <T extends numeric,>(x: T, y: T) =>
+	(max(abs(x), abs(y)) / min(abs(x), abs(y))) as T
+```
+
+## See also
+[Rust `lib`](https://github.com/Rudxain/abs_ratio/blob/main/src/lib.rs)