From 4bda9625fca300cc79fa4b25a07666fb163e88a2 Mon Sep 17 00:00:00 2001
From: Chris Faulhaber <chris@codealchemy.org>
Date: Fri, 30 Oct 2015 22:54:59 -0400
Subject: [PATCH] Add weather forecast algorithm.

---
 research/weather.md | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 research/weather.md

diff --git a/research/weather.md b/research/weather.md
new file mode 100644
index 000000000..490607e2f
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+++ b/research/weather.md
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+The current weather of a zone is based on the current unix epoch, and a zone weather table (WeatherRate).
+A forecast target integer is first calculated.  This value to the frequency of the zone's weather.
+When the number is less than the cumulative rate at which a weather pattern occurs, that weather will appear in the zone.
+For example, in Gridania it's raining 20% of the time, and foggy 10%. It rains when the number is < 20, and foggy when it's >= 20 and < 30, and so on.
+
+````js
+calculateForecastTarget: function(lDate) { 
+    // Thanks to Rogueadyn's SaintCoinach library for this calculation.
+    // lDate is the current local time.
+
+    var unixSeconds = parseInt(lDate.getTime() / 1000);
+    // Get Eorzea hour for weather start
+    var bell = unixSeconds / 175;
+
+    // Do the magic 'cause for calculations 16:00 is 0, 00:00 is 8 and 08:00 is 16
+    var increment = (bell + 8 - (bell % 8)) % 24;
+
+    // Take Eorzea days since unix epoch
+    var totalDays = unixSeconds / 4200;
+    totalDays = (totalDays << 32) >>> 0; // Convert to uint
+
+    // 0x64 = 100
+    var calcBase = totalDays * 100 + increment;
+
+    // 0xB = 11
+    var step1 = (calcBase << 11) ^ calcBase;
+    var step2 = (step1 >>> 8) ^ step1;
+
+    // 0x64 = 100
+    return step2 % 100;
+}
+````
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