fixup! Add Number#humanize

src/number.cr

@@ -230,7 +230,7 @@ struct Number
   end
 
   # Default SI prefixes ordered by magnitude.
-  SI_PREFIXES = {nil, 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y', nil, 'y', 'z', 'a', 'f', 'p', 'n', 'µ', 'm'}
+  SI_PREFIXES = { {'y', 'z', 'a', 'f', 'p', 'n', 'µ', 'm'}, {nil, 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y'} }
 
   # SI prefixes used by `#humanize`. Equal to `SI_PREFIXES` but prepends the
   # prefix with a space charater.
@@ -244,10 +244,10 @@ struct Number
   # ```
   # Number.si_prefix(3) # => 'k'
   # ```
-  def self.si_prefix(magnitude : Int) : Char?
-    max = SI_PREFIXES.size / 2
-    index = (magnitude / 3).clamp(-max..max)
-    SI_PREFIXES[index]
+  def self.si_prefix(magnitude : Int, prefixes = SI_PREFIXES) : Char?
+    index = (magnitude / 3)
+    prefixes = prefixes[magnitude < 0 ? 0 : 1]
+    prefixes[index.clamp((-prefixes.size + 1)..(prefixes.size - 1))]
   end
 
   # :nodoc:
@@ -285,9 +285,7 @@ struct Number
   def humanize(io : IO, precision = 3, separator = '.', delimiter = ',', *, base = 10 ** 3, significant = true, prefixes : Indexable = SI_PREFIXES) : Nil
     humanize(io, precision, separator, delimiter, base: base, significant: significant) do |magnitude, _|
       magnitude = Number.prefix_index(magnitude)
-      max = prefixes.size / 2
-      index = (magnitude / 3).clamp(-max..max)
-      {magnitude, prefixes[index]}
+      {magnitude, Number.si_prefix(magnitude, prefixes)}
     end
   end