Format decimal numbers with BigDecimal instead of Float

lib/cldr/format/decimal.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "bigdecimal"
+
 module Cldr
   module Format
     class Decimal
@@ -15,7 +17,7 @@ def initialize(format, symbols = {})
       end
 
       def apply(number, options = {})
-        number = Float(number)
+        number = BigDecimal(number) unless number.is_a?(::Numeric)
         format = number.abs == number ? positive : negative
         format.apply(number, options)
       rescue TypeError, ArgumentError

lib/cldr/format/decimal/number.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "bigdecimal"
+
 module Cldr
   module Format
     class Decimal
@@ -33,12 +35,13 @@ def parse_format(format, symbols = {})
         def parse_number(number, options = {})
           precision = options[:precision] || fraction_format.precision
           number = round_to(number, precision)
-          number.abs.to_s.split(".")
+          number.abs.to_s("F").split(".")
         end
 
+        # BigDecimal keeps full precision, avoids Float scientific notation, and
+        # rounds half-even (ties to even) as CLDR / UTS #35 mandates.
         def round_to(number, precision)
-          factor = 10**precision
-          (number * factor).round.to_f / factor
+          BigDecimal(number.to_r, 0).round(precision, half: :even)
         end
       end
     end

test/format/currency_test.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require File.expand_path(File.join(File.dirname(__FILE__) + "/../test_helper"))
+
+class TestCldrCurrencyFormat < Test::Unit::TestCase
+  test "interpolates the currency symbol" do
+    assert_equal "$123.45", Cldr::Format::Currency.new("¤0.00").apply(123.45, currency: "$")
+  end
+
+  test "rounds half-even like the decimal formatter" do
+    assert_equal "$0.12", Cldr::Format::Currency.new("¤0.00").apply(0.125, currency: "$")
+    assert_equal "$2", Cldr::Format::Currency.new("¤0").apply(2.5, currency: "$")
+  end
+
+  test "formats a large amount without scientific notation" do
+    assert_equal "$12,345,678,901,234,567,890", Cldr::Format::Currency.new("¤#,##0").apply(12345678901234567890, currency: "$")
+  end
+end

test/format/decimal/number_test.rb

@@ -74,4 +74,34 @@ class TestCldrDecimalNumberFormat < Test::Unit::TestCase
   test "cldr example 00000.0000 => 01234,5670" do
     assert_equal "01234,5670", Cldr::Format::Decimal::Number.new("00000.0000", decimal: ",", group: " ").apply(1234.567)
   end
+
+  # CLDR / UTS #35 rounds half-even; expected values cross-checked against ICU and Babel 2.17.
+  test "rounds exact halves to even at precision 2" do
+    number = Cldr::Format::Decimal::Number.new("0.00")
+    assert_equal "0.12", number.apply(0.125)
+    assert_equal "0.62", number.apply(0.625)
+    assert_equal "0.38", number.apply(0.375)
+    assert_equal "0.88", number.apply(0.875)
+    assert_equal "2.12", number.apply(2.125)
+  end
+
+  test "rounds exact halves to even at precision 0" do
+    number = Cldr::Format::Decimal::Number.new("0")
+    assert_equal "0", number.apply(0.5)
+    assert_equal "2", number.apply(1.5)
+    assert_equal "2", number.apply(2.5)
+    assert_equal "4", number.apply(3.5)
+    assert_equal "4", number.apply(4.5)
+  end
+
+  test "formats large integers without scientific notation" do
+    number = Cldr::Format::Decimal::Number.new("#,##0")
+    assert_equal "1,000,000,000,000,000", number.apply(10**15)
+    assert_equal "10,000,000,000,000,000", number.apply(10**16)
+    assert_equal "12,345,678,901,234,567,890", number.apply(12345678901234567890)
+  end
+
+  test "keeps full precision for integers above 2**53" do
+    assert_equal "9,007,199,254,740,993", Cldr::Format::Decimal::Number.new("#,##0").apply(2**53 + 1)
+  end
 end

test/format/decimal_test.rb

@@ -18,4 +18,18 @@ class TestCldrDecimalFormat < Test::Unit::TestCase
   test "positive/negative patterns, negative number" do
     assert_equal "-123", Cldr::Format::Decimal.new("#;-#").apply(-123)
   end
+
+  test "rounds half-even through the public formatter" do
+    assert_equal "2", Cldr::Format::Decimal.new("0").apply(2.5)
+    assert_equal "-2", Cldr::Format::Decimal.new("0").apply(-2.5)
+    assert_equal "0.12", Cldr::Format::Decimal.new("0.00").apply(0.125)
+  end
+
+  test "formats a large integer without precision loss" do
+    assert_equal "12,345,678,901,234,567,890", Cldr::Format::Decimal.new("#,##0").apply(12345678901234567890)
+  end
+
+  test "leaves a non-numeric argument untouched" do
+    assert_equal "abc", Cldr::Format::Decimal.new("#").apply("abc")
+  end
 end

test/format/percent_test.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require File.expand_path(File.join(File.dirname(__FILE__) + "/../test_helper"))
+
+class TestCldrPercentFormat < Test::Unit::TestCase
+  test "interpolates the percent sign" do
+    assert_equal "12.34 %", Cldr::Format::Percent.new("0.00 %").apply(12.34)
+  end
+
+  test "rounds half-even like the decimal formatter" do
+    assert_equal "0.12 %", Cldr::Format::Percent.new("0.00 %").apply(0.125)
+    assert_equal "2 %", Cldr::Format::Percent.new("0 %").apply(2.5)
+  end
+end