added flip_sign

README.md

@@ -24,6 +24,7 @@ The following functions are supported:
 - [divide](#divide)
 - [exp](#exp)
 - [factorial](#factorial)
+- [flip_sign](#flip-sign)
 - [floor](#floor)
 - [hypotenuse](#hypotenuse)
 - [max](#max)
@@ -169,6 +170,21 @@ factorial("10");
 "3628800"
 ```
 
+### flip_sign
+```js
+import flip_sign from "preciso/flip_sign.js";
+
+flip_sign(10);
+-10
+
+flip_sign(-99)
+99
+
+// zero has no sign change
+flip_sign(0)
+0
+```
+
 ### floor
 ```js
 import floor from "preciso/floor.js";

flip_sign.js

@@ -0,0 +1,22 @@
+"use strict";
+
+const absolute = require("./absolute.js");
+const clean = require("./clean.js");
+const sign = require("./sign.js");
+
+function flip_sign(n) {
+  n = clean(n);
+  const s = sign(n);
+  if (s === "") {
+    return n;
+  } else if (s === "-") {
+    return absolute(n);
+  } else if (s === "+") {
+    return "-" + n;
+  }
+
+  return sum;
+}
+
+module.exports = flip_sign;
+module.exports.default = flip_sign;

preciso.d.ts

@@ -10,6 +10,7 @@ export function cube(
 export function cube_root(radicand: string, options?: { imaginary?: boolean; max_decimal_digits?: number }): string;
 export function divide(dividend: string, divisor: string, options?: { max_decimal_digits: number; ellipsis: boolean }): string;
 export function factorial(n: string): string;
+export function flip_sign(n: string): string;
 export function floor(n: string): string;
 
 // you can also pass in max(a, b, c, d) but I'm not sure how to type that

preciso.js

@@ -19,6 +19,7 @@ const eulers_number = require("./eulers_number.js");
 const exp = require("./exp.js");
 const expand = require("./expand.js");
 const factorial = require("./factorial.js");
+const flip_sign = require("./flip_sign.js");
 const floor = require("./floor.js");
 const fraction = require("./fraction.js");
 // const gregory_leibniz = require("./gregory_leibniz.js");
@@ -81,6 +82,7 @@ const module_exports = {
   exp,
   expand,
   factorial,
+  flip_sign,
   floor,
   fraction,
   // gregory_leibniz,

test.js

@@ -21,6 +21,7 @@ const {
   eulers_number,
   exp,
   factorial,
+  flip_sign,
   fraction,
   floor,
   // gregory_leibniz,