1 files changed, 92 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
new file mode 100644
index 0000000000..c42354fc83
--- /dev/null
+++ b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
@@ -0,0 +1,92 @@
+module ActiveSupport
+  module NumberHelper
+    class NumberToRoundedConverter < NumberConverter # :nodoc:
+      self.namespace      = :precision
+      self.validate_float = true
+
+      def convert
+        precision = options.delete :precision
+        significant = options.delete :significant
+
+        case number
+        when Float, String
+          @number = BigDecimal(number.to_s)
+        when Rational
+          if significant
+            @number = BigDecimal(number, digit_count(number.to_i) + precision)
+          else
+            @number = BigDecimal(number, precision)
+          end
+        else
+          @number = number.to_d
+        end
+
+        if significant && precision > 0
+          digits, rounded_number = digits_and_rounded_number(precision)
+          precision -= digits
+          precision = 0 if precision < 0 # don't let it be negative
+        else
+          rounded_number = number.round(precision)
+          rounded_number = rounded_number.to_i if precision == 0
+          rounded_number = rounded_number.abs if rounded_number.zero? # prevent showing negative zeros
+        end
+
+        formatted_string =
+          case rounded_number
+          when BigDecimal
+            s = rounded_number.to_s('F') + '0'*precision
+            a, b = s.split('.', 2)
+            a + '.' + b[0, precision]
+          else
+            "%01.#{precision}f" % rounded_number
+          end
+
+        delimited_number = NumberToDelimitedConverter.convert(formatted_string, options)
+        format_number(delimited_number)
+      end
+
+      private
+
+        def digits_and_rounded_number(precision)
+          if zero?
+            [1, 0]
+          else
+            digits = digit_count(number)
+            multiplier = 10 ** (digits - precision)
+            rounded_number = calculate_rounded_number(multiplier)
+            digits = digit_count(rounded_number) # After rounding, the number of digits may have changed
+            [digits, rounded_number]
+          end
+        end
+
+        def calculate_rounded_number(multiplier)
+          (number / BigDecimal.new(multiplier.to_f.to_s)).round * multiplier
+        end
+
+        def digit_count(number)
+          (Math.log10(absolute_number(number)) + 1).floor
+        end
+
+        def strip_insignificant_zeros
+          options[:strip_insignificant_zeros]
+        end
+
+        def format_number(number)
+          if strip_insignificant_zeros
+            escaped_separator = Regexp.escape(options[:separator])
+            number.sub(/(#{escaped_separator})(\d*[1-9])?0+\z/, '\1\2').sub(/#{escaped_separator}\z/, '')
+          else
+            number
+          end
+        end
+
+        def absolute_number(number)
+          number.respond_to?(:abs) ? number.abs : number.to_d.abs
+        end
+
+        def zero?
+          number.respond_to?(:zero?) ? number.zero? : number.to_d.zero?
+        end
+    end
+  end
+end