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[rails.git] / lib / short_link.rb

diff --git a/lib/short_link.rb b/lib/short_link.rb
index afcf1ef37f5462a0b83b4cc3d85a283a24e0dc7d..43d64041e6b7a765114f36ea4b7e302dd3ac392a 100644 (file)
--- a/lib/short_link.rb
+++ b/lib/short_link.rb
@@ -5,14 +5,13 @@
 # Each character encodes 3 bits of x and 3 of y, so there are extra characters
 # tacked on the end to make the zoom levels "work".
 module ShortLink
-
   # array of 64 chars to encode 6 bits. this is almost like base64 encoding, but
-  # the symbolic chars are different, as base64's + and / aren't very 
+  # the symbolic chars are different, as base64's + and / aren't very
   # URL-friendly.
-  ARRAY = ('A'..'Z').to_a + ('a'..'z').to_a + ('0'..'9').to_a + ['_','@']
+  ARRAY = ("A".."Z").to_a + ("a".."z").to_a + ("0".."9").to_a + ["_", "~"]
 
   ##
-  # Given a string encoding a location, returns the [lon, lat, z] tuple of that 
+  # Given a string encoding a location, returns the [lon, lat, z] tuple of that
   # location.
   def self.decode(str)
     x = 0
@@ -20,14 +19,24 @@ module ShortLink
     z = 0
     z_offset = 0
 
+    # keep support for old shortlinks which use the @ character, now
+    # replaced by the ~ character because twitter is horribly broken
+    # and we can't have that.
+    str.tr!("@", "~")
+
     str.each_char do |c|
       t = ARRAY.index c
       if t.nil?
         z_offset -= 1
       else
         3.times do
-          x <<= 1; x = x | 1 unless (t & 32).zero?; t <<= 1
-          y <<= 1; y = y | 1 unless (t & 32).zero?; t <<= 1
+          x <<= 1
+          x |= 1 unless (t & 32).zero?
+          t <<= 1
+
+          y <<= 1
+          y |= 1 unless (t & 32).zero?
+          t <<= 1
         end
         z += 3
       end
@@ -37,33 +46,33 @@ module ShortLink
     y <<= (32 - z)
 
     # project the parameters back to their coordinate ranges.
-    [(x * 360.0 / 2**32) - 180.0, 
-     (y * 180.0 / 2**32) - 90.0, 
+    [(x * 360.0 / 2**32) - 180.0,
+     (y * 180.0 / 2**32) - 90.0,
      z - 8 - (z_offset % 3)]
   end
 
   ##
   # given a location and zoom, return a short string representing it.
   def self.encode(lon, lat, z)
-    code = interleave_bits(((lon + 180.0) * 2**32 / 360.0).to_i, 
-                           ((lat +  90.0) * 2**32 / 180.0).to_i)
+    code = interleave_bits(((lon + 180.0) * 2**32 / 360.0).to_i,
+                           ((lat + 90.0) * 2**32 / 180.0).to_i)
     str = ""
     # add eight to the zoom level, which approximates an accuracy of
     # one pixel in a tile.
-    ((z + 8)/3.0).ceil.times do |i|
+    ((z + 8) / 3.0).ceil.times do |i|
       digit = (code >> (58 - 6 * i)) & 0x3f
       str << ARRAY[digit]
     end
     # append characters onto the end of the string to represent
     # partial zoom levels (characters themselves have a granularity
     # of 3 zoom levels).
-    ((z + 8) % 3).times { str << "=" }
-    
-    return str
+    ((z + 8) % 3).times { str << "-" }
+
+    str
   end
 
   private
-  
+
   ##
   # interleaves the bits of two 32-bit numbers. the result is known
   # as a Morton code.
@@ -75,5 +84,4 @@ module ShortLink
     end
     c
   end
-
 end