From d9344ccd68dbe21eb5af6d0575b5b84b9f8513aa Mon Sep 17 00:00:00 2001
From: Joe Wreschnig <joe.wreschnig@gmail.com>
Date: Mon, 19 May 2014 03:40:40 +0200
Subject: [PATCH] Have numericLerp work in fixed point based on the longest
 operand. Restrict the set of strings considered numbers to those JS
 reasonable can treat as numbers.

---
 demo.html            |  2 +-
 string-lerp.js       | 10 +++++-----
 tests/string-lerp.js |  6 ++++++
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/demo.html b/demo.html
index 81941dc..de1902d 100644
--- a/demo.html
+++ b/demo.html
@@ -17,7 +17,7 @@
           ["Do you like green eggs and ham?", "I do not like them, Sam-I-am."],
           ["apple core", "core dump"],
           ["rgb(255, 0, 0)", "rgb(0, 128, 255)"],
-          ["1.5 + 1.5 = 3.0", "3 + 7 = 10"],
+          ["1.50 + 1.50 = 3.0", "3 + 7 = 10"],
           ["ZALGO̸", "ZA̢LG͜O"],
           ["", "Typing, one letter at a time."],
           ["( ﾉﾟ▽ﾟ)ﾉ", "( ╯︵╰)"]
diff --git a/string-lerp.js b/string-lerp.js
index 607abc1..46a55bf 100644
--- a/string-lerp.js
+++ b/string-lerp.js
@@ -154,7 +154,7 @@
         return patch(partial, target);
     }
 
-    var NUMBERS = /(-?\d+(?:\.\d+)?)/g;
+    var NUMBERS = /(-?\d{1,20}(?:\.\d{1,20})?)/g;
 
     function areNumericTwins(source, target) {
         /** Check if a and b differ only in numerals */
@@ -184,7 +184,6 @@
             numerals gives undefined results.
         */
 
-        // TODO: Try to preserve precision of the original numbers.
         var sourceParts = source.split(NUMBERS);
         var targetParts = target.split(NUMBERS);
         var destParts = targetParts;
@@ -194,9 +193,10 @@
             var part = nlerp(+sourcePart, +targetPart, amount);
             var sourcePoint = sourcePart.indexOf(".");
             var targetPoint = targetPart.indexOf(".");
-            if (sourcePoint === -1 && targetPoint === -1)
-                part = Math.round(part);
-            targetParts[i] = part.toString();
+            var point = Math.max(
+                sourcePoint >= 0 ? (sourcePart.length - 1) - sourcePoint : 0,
+                targetPoint >= 0 ? (targetPart.length - 1) - targetPoint : 0);
+            targetParts[i] = part.toFixed(point);
         }
         return targetParts.join("");
     }
diff --git a/tests/string-lerp.js b/tests/string-lerp.js
index 0a68921..2eccba6 100644
--- a/tests/string-lerp.js
+++ b/tests/string-lerp.js
@@ -157,6 +157,12 @@ JS.Test.describe('numeric lerp', function () { with (this) {
         assertEqual("12.3", lerp("0.0", "100.0", 0.123));
     }});
 
+    it("thinks about precision", function () { with (this) {
+        assertEqual("12.30", lerp("0", "100.00", 0.123));
+        assertEqual("12.30", lerp("0.00", "100", 0.123));
+        assertEqual("12.300", lerp("0.000", "100.000", 0.123));
+    }});
+
     it("computes parameters outside [0, 1]", function () { with (this) {
         assertEqual("Giving 110%", lerp("Giving 0%", "Giving 100%", 1.1));
     }});
-- 
2.20.1