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GH-48703: [Ruby] Add support for reading decimal256 array #48704

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Merged
kou merged 1 commit into from
Jan 2, 2026
Merged

GH-48703: [Ruby] Add support for reading decimal256 array #48704

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39 changes: 28 additions & 11 deletions ruby/red-arrow-format/lib/arrow-format/array.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -309,40 +309,57 @@ def to_a
end

class DecimalArray < FixedSizeBinaryArray
end

class Decimal128Array < DecimalArray
def to_a
byte_width = @type.byte_width
buffer_types = [:u64, :s64] # TODO: big endian support
buffer_types = [:u64] * (byte_width / 8 - 1) + [:s64]
values = 0.step(@size * byte_width - 1, byte_width).collect do |offset|
@values_buffer.get_values(buffer_types, offset)
end
apply_validity(values).collect do |value|
if value.nil?
nil
else
low, high = value
BigDecimal(format_value(low, high))
BigDecimal(format_value(value))
end
end
end

private
def format_value(low, high)
def format_value(components)
highest = components.last
width = @type.precision
width += 1 if high < 0
value = (high << 64) + low
string = value.to_s.ljust(width, "0")
width += 1 if highest < 0
value = 0
components.reverse_each do |component|
value = (value << 64) + component
end
string = value.to_s
if @type.scale < 0
string << ("0" * [email protected])
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@hiroyuki-sato hiroyuki-sato Jan 2, 2026 •
edited
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(This part is the out of scope in this PR). It seems storange.

"0" * -4
ArgumentError: negative argument (ArgumentError)
from (pry):3:in 'String#*'

scale: -3 and value 123 formats to 123000?

string << ("0" * @type.scale)

?

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@kou kou Jan 2, 2026

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Yes. 123 + scale: -3 is 123000.

BTW, why did you try "0" * -4? In this context, @type.scale is negative. So "0" * --4 should be tried for the case.

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@hiroyuki-sato hiroyuki-sato Jan 2, 2026

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Thank you for your comment. It was misunderstanding.

elsif @type.scale > 0
string[[email protected], 0] = "."
n_digits = string.bytesize
n_digits -= 1 if value < 0
if n_digits < @type.scale
prefix = "0." + ("0" * (@type.scale - n_digits - 1))
if value < 0
string[1, 0] = prefix
else
string[0, 0] = prefix
end
else
string[[email protected], 0] = "."
end
end
string
end
end

class Decimal128Array < DecimalArray
end

class Decimal256Array < DecimalArray
end

class VariableSizeListArray < Array
def initialize(type, size, validity_buffer, offsets_buffer, child)
super(type, size, validity_buffer)
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2 changes: 2 additions & 0 deletions ruby/red-arrow-format/lib/arrow-format/readable.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,8 @@ def read_field(fb_field)
case fb_type.bit_width
when 128
type = Decimal128Type.new(fb_type.precision, fb_type.scale)
when 256
type = Decimal256Type.new(fb_type.precision, fb_type.scale)
end
end
Field.new(fb_field.name, type, fb_field.nullable?)
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14 changes: 14 additions & 0 deletions ruby/red-arrow-format/lib/arrow-format/type.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -522,6 +522,20 @@ def build_array(size, validity_buffer, values_buffer)
end
end

class Decimal256Type < DecimalType
def initialize(precision, scale)
super(32, precision, scale)
end

def name
"Decimal256"
end

def build_array(size, validity_buffer, values_buffer)
Decimal256Array.new(self, size, validity_buffer, values_buffer)
end
end

class VariableSizeListType < Type
attr_reader :child
def initialize(child)
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52 changes: 47 additions & 5 deletions ruby/red-arrow-format/test/test-reader.rb
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Expand Up @@ -676,19 +676,61 @@ def test_read

sub_test_case("Decimal128") do
def build_array
@positive = "12345678901234567890123456789012345.678"
@negative = "-12345678901234567890123456789012345.67"
@positive_small = "1.200"
@positive_large = ("1234567890" * 3) + "12345.678"
@negative_small = "-1.200"
@negative_large = "-" + ("1234567890" * 3) + "12345.678"
Arrow::Decimal128Array.new({precision: 38, scale: 3},
[@positive, nil, @negative])
[
@positive_large,
@positive_small,
nil,
@negative_small,
@negative_large,
])
end

def test_read
assert_equal([
{
"value" => [
BigDecimal(@positive),
BigDecimal(@positive_large),
BigDecimal(@positive_small),
nil,
BigDecimal(@negative),
BigDecimal(@negative_small),
BigDecimal(@negative_large),
],
},
],
read)
end
end

sub_test_case("Decimal256") do
def build_array
@positive_small = "1.200"
@positive_large = ("1234567890" * 7) + "123.456"
@negative_small = "-1.200"
@negative_large = "-" + ("1234567890" * 7) + "123.456"
Arrow::Decimal256Array.new({precision: 76, scale: 3},
[
@positive_large,
@positive_small,
nil,
@negative_small,
@negative_large,
])
end

def test_read
assert_equal([
{
"value" => [
BigDecimal(@positive_large),
BigDecimal(@positive_small),
nil,
BigDecimal(@negative_small),
BigDecimal(@negative_large),
],
},
],
Expand Down
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