From: Scott Worley <scottworley@scottworley.com>
Date: Thu, 23 May 2019 21:37:46 +0000 (-0700)
Subject: Handle the fully-deductible case
X-Git-Tag: v1.0~13
X-Git-Url: http://git.scottworley.com/inverse-tax/commitdiff_plain/49188cbe174f6f0559037bb2f6e51300dac90a85?hp=82b7a49862ffba0bcd9e6b5500b4ed2e901444e8

Handle the fully-deductible case
---

diff --git a/tax.js b/tax.js
index 7f32f74..d9bd34c 100644
--- a/tax.js
+++ b/tax.js
@@ -53,8 +53,6 @@ function merge_tax_tables(t1, t2) {
 }
 
 function invert(table) {
-  if (table.length == 0) return x => x;
-
   // Here we solve
   //   net = m * gross + b
   // for gross:
@@ -90,5 +88,6 @@ function invert(table) {
         return (net - b) / m;
       }
     }
+    return net;
   };
 }
diff --git a/tax.test.js b/tax.test.js
index 14c48c0..125cc20 100644
--- a/tax.test.js
+++ b/tax.test.js
@@ -57,5 +57,6 @@ test("invert", () => {
   assert.strictEqual(invert([                  ])(10), 10);
   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
+  assert.strictEqual(invert([[10, Infinity, .1]])( 9),  9);
   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
 });