Support decimal negative scale

arrow-array/src/array/primitive_array.rs

@@ -1002,7 +1002,7 @@ impl<T: DecimalType + ArrowPrimitiveType> PrimitiveArray<T> {
     pub fn with_precision_and_scale(
         self,
         precision: u8,
-        scale: u8,
+        scale: i8,
     ) -> Result<Self, ArrowError>
     where
         Self: Sized,
@@ -1023,7 +1023,7 @@ impl<T: DecimalType + ArrowPrimitiveType> PrimitiveArray<T> {
     fn validate_precision_scale(
         &self,
         precision: u8,
-        scale: u8,
+        scale: i8,
     ) -> Result<(), ArrowError> {
         if precision > T::MAX_PRECISION {
             return Err(ArrowError::InvalidArgumentError(format!(
@@ -1039,7 +1039,14 @@ impl<T: DecimalType + ArrowPrimitiveType> PrimitiveArray<T> {
                 Decimal128Type::MAX_SCALE
             )));
         }
-        if scale > precision {
+        if scale < -T::MAX_SCALE {
+            return Err(ArrowError::InvalidArgumentError(format!(
+                "scale {} is smaller than min {}",
+                scale,
+                -Decimal128Type::MAX_SCALE
+            )));
+        }
+        if scale > 0 && scale as u8 > precision {
             return Err(ArrowError::InvalidArgumentError(format!(
                 "scale {} is greater than precision {}",
                 scale, precision
@@ -1095,7 +1102,7 @@ impl<T: DecimalType + ArrowPrimitiveType> PrimitiveArray<T> {
     }
 
     /// Returns the decimal scale of this array
-    pub fn scale(&self) -> u8 {
+    pub fn scale(&self) -> i8 {
         match T::BYTE_LENGTH {
             16 => {
                 if let DataType::Decimal128(_, s) = self.data().data_type() {

arrow-array/src/types.rs

@@ -491,15 +491,15 @@ pub trait DecimalType:
 {
     const BYTE_LENGTH: usize;
     const MAX_PRECISION: u8;
-    const MAX_SCALE: u8;
-    const TYPE_CONSTRUCTOR: fn(u8, u8) -> DataType;
+    const MAX_SCALE: i8;
+    const TYPE_CONSTRUCTOR: fn(u8, i8) -> DataType;
     const DEFAULT_TYPE: DataType;
 
     /// "Decimal128" or "Decimal256", for use in error messages
     const PREFIX: &'static str;
 
     /// Formats the decimal value with the provided precision and scale
-    fn format_decimal(value: Self::Native, precision: u8, scale: u8) -> String;
+    fn format_decimal(value: Self::Native, precision: u8, scale: i8) -> String;
 
     /// Validates that `value` contains no more than `precision` decimal digits
     fn validate_decimal_precision(
@@ -515,14 +515,14 @@ pub struct Decimal128Type {}
 impl DecimalType for Decimal128Type {
     const BYTE_LENGTH: usize = 16;
     const MAX_PRECISION: u8 = DECIMAL128_MAX_PRECISION;
-    const MAX_SCALE: u8 = DECIMAL128_MAX_SCALE;
-    const TYPE_CONSTRUCTOR: fn(u8, u8) -> DataType = DataType::Decimal128;
+    const MAX_SCALE: i8 = DECIMAL128_MAX_SCALE;
+    const TYPE_CONSTRUCTOR: fn(u8, i8) -> DataType = DataType::Decimal128;
     const DEFAULT_TYPE: DataType =
         DataType::Decimal128(DECIMAL128_MAX_PRECISION, DECIMAL_DEFAULT_SCALE);
     const PREFIX: &'static str = "Decimal128";
 
-    fn format_decimal(value: Self::Native, precision: u8, scale: u8) -> String {
-        format_decimal_str(&value.to_string(), precision as usize, scale as usize)
+    fn format_decimal(value: Self::Native, precision: u8, scale: i8) -> String {
+        format_decimal_str(&value.to_string(), precision as usize, scale)
     }
 
     fn validate_decimal_precision(num: i128, precision: u8) -> Result<(), ArrowError> {
@@ -543,14 +543,14 @@ pub struct Decimal256Type {}
 impl DecimalType for Decimal256Type {
     const BYTE_LENGTH: usize = 32;
     const MAX_PRECISION: u8 = DECIMAL256_MAX_PRECISION;
-    const MAX_SCALE: u8 = DECIMAL256_MAX_SCALE;
-    const TYPE_CONSTRUCTOR: fn(u8, u8) -> DataType = DataType::Decimal256;
+    const MAX_SCALE: i8 = DECIMAL256_MAX_SCALE;
+    const TYPE_CONSTRUCTOR: fn(u8, i8) -> DataType = DataType::Decimal256;
     const DEFAULT_TYPE: DataType =
         DataType::Decimal256(DECIMAL256_MAX_PRECISION, DECIMAL_DEFAULT_SCALE);
     const PREFIX: &'static str = "Decimal256";
 
-    fn format_decimal(value: Self::Native, precision: u8, scale: u8) -> String {
-        format_decimal_str(&value.to_string(), precision as usize, scale as usize)
+    fn format_decimal(value: Self::Native, precision: u8, scale: i8) -> String {
+        format_decimal_str(&value.to_string(), precision as usize, scale)
     }
 
     fn validate_decimal_precision(num: i256, precision: u8) -> Result<(), ArrowError> {
@@ -564,7 +564,7 @@ impl ArrowPrimitiveType for Decimal256Type {
     const DATA_TYPE: DataType = <Self as DecimalType>::DEFAULT_TYPE;
 }
 
-fn format_decimal_str(value_str: &str, precision: usize, scale: usize) -> String {
+fn format_decimal_str(value_str: &str, precision: usize, scale: i8) -> String {
     let (sign, rest) = match value_str.strip_prefix('-') {
         Some(stripped) => ("-", stripped),
         None => ("", value_str),
@@ -574,13 +574,16 @@ fn format_decimal_str(value_str: &str, precision: usize, scale: usize) -> String
 
     if scale == 0 {
         value_str.to_string()
-    } else if rest.len() > scale {
+    } else if scale < 0 {
+        let padding = value_str.len() + scale.unsigned_abs() as usize;
+        format!("{:0<width$}", value_str, width = padding)
+    } else if rest.len() > scale as usize {
         // Decimal separator is in the middle of the string
-        let (whole, decimal) = value_str.split_at(value_str.len() - scale);
+        let (whole, decimal) = value_str.split_at(value_str.len() - scale as usize);
         format!("{}.{}", whole, decimal)
     } else {
         // String has to be padded
-        format!("{}0.{:0>width$}", sign, rest, width = scale)
+        format!("{}0.{:0>width$}", sign, rest, width = scale as usize)
     }
 }
 

arrow-cast/src/cast.rs

@@ -319,7 +319,7 @@ fn cast_integer_to_decimal<
 >(
     array: &PrimitiveArray<T>,
     precision: u8,
-    scale: u8,
+    scale: i8,
     base: M,
     cast_options: &CastOptions,
 ) -> Result<ArrayRef, ArrowError>
@@ -352,7 +352,7 @@ where
 fn cast_floating_point_to_decimal128<T: ArrowPrimitiveType>(
     array: &PrimitiveArray<T>,
     precision: u8,
-    scale: u8,
+    scale: i8,
     cast_options: &CastOptions,
 ) -> Result<ArrayRef, ArrowError>
 where
@@ -391,7 +391,7 @@ where
 fn cast_floating_point_to_decimal256<T: ArrowPrimitiveType>(
     array: &PrimitiveArray<T>,
     precision: u8,
-    scale: u8,
+    scale: i8,
     cast_options: &CastOptions,
 ) -> Result<ArrayRef, ArrowError>
 where
@@ -437,7 +437,7 @@ fn cast_reinterpret_arrays<
 fn cast_decimal_to_integer<D, T>(
     array: &ArrayRef,
     base: D::Native,
-    scale: u8,
+    scale: i8,
     cast_options: &CastOptions,
 ) -> Result<ArrayRef, ArrowError>
 where
@@ -1921,9 +1921,9 @@ fn cast_decimal_to_decimal_with_option<
     const BYTE_WIDTH2: usize,
 >(
     array: &ArrayRef,
-    input_scale: &u8,
+    input_scale: &i8,
     output_precision: &u8,
-    output_scale: &u8,
+    output_scale: &i8,
     cast_options: &CastOptions,
 ) -> Result<ArrayRef, ArrowError> {
     if cast_options.safe {
@@ -1947,9 +1947,9 @@ fn cast_decimal_to_decimal_with_option<
 /// the array values when cast failures happen.
 fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1: usize, const BYTE_WIDTH2: usize>(
     array: &ArrayRef,
-    input_scale: &u8,
+    input_scale: &i8,
     output_precision: &u8,
-    output_scale: &u8,
+    output_scale: &i8,
 ) -> Result<ArrayRef, ArrowError> {
     if input_scale > output_scale {
         // For example, input_scale is 4 and output_scale is 3;
@@ -2062,9 +2062,9 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1: usize, const BYTE_WIDTH2: usi
 /// cast failure happens.
 fn cast_decimal_to_decimal<const BYTE_WIDTH1: usize, const BYTE_WIDTH2: usize>(
     array: &ArrayRef,
-    input_scale: &u8,
+    input_scale: &i8,
     output_precision: &u8,
-    output_scale: &u8,
+    output_scale: &i8,
 ) -> Result<ArrayRef, ArrowError> {
     if input_scale > output_scale {
         // For example, input_scale is 4 and output_scale is 3;
@@ -3540,7 +3540,7 @@ mod tests {
     fn create_decimal_array(
         array: Vec<Option<i128>>,
         precision: u8,
-        scale: u8,
+        scale: i8,
     ) -> Result<Decimal128Array, ArrowError> {
         array
             .into_iter()
@@ -3551,7 +3551,7 @@ mod tests {
     fn create_decimal256_array(
         array: Vec<Option<i256>>,
         precision: u8,
-        scale: u8,
+        scale: i8,
     ) -> Result<Decimal256Array, ArrowError> {
         array
             .into_iter()
@@ -7206,4 +7206,32 @@ mod tests {
             err
         );
     }
+
+    #[test]
+    fn test_cast_decimal128_to_decimal128_negative_scale() {
+        let input_type = DataType::Decimal128(20, 0);
+        let output_type = DataType::Decimal128(20, -1);
+        assert!(can_cast_types(&input_type, &output_type));
+        let array = vec![Some(1123456), Some(2123456), Some(3123456), None];
+        let input_decimal_array = create_decimal_array(array, 20, 0).unwrap();
+        let array = Arc::new(input_decimal_array) as ArrayRef;
+        generate_cast_test_case!(
+            &array,
+            Decimal128Array,
+            &output_type,
+            vec![
+                Some(112345_i128),
+                Some(212345_i128),
+                Some(312345_i128),
+                None
+            ]
+        );
+
+        let casted_array = cast(&array, &output_type).unwrap();
+        let decimal_arr = as_primitive_array::<Decimal128Type>(&casted_array);
+
+        assert_eq!("1123450", decimal_arr.value_as_string(0));
+        assert_eq!("2123450", decimal_arr.value_as_string(1));
+        assert_eq!("3123450", decimal_arr.value_as_string(2));
+    }
 }

arrow-csv/src/reader.rs

@@ -721,7 +721,7 @@ fn build_decimal_array(
     rows: &[StringRecord],
     col_idx: usize,
     precision: u8,
-    scale: u8,
+    scale: i8,
 ) -> Result<ArrayRef, ArrowError> {
     let mut decimal_builder = Decimal128Builder::with_capacity(rows.len());
     for row in rows {
@@ -762,13 +762,13 @@ fn build_decimal_array(
 fn parse_decimal_with_parameter(
     s: &str,
     precision: u8,
-    scale: u8,
+    scale: i8,
 ) -> Result<i128, ArrowError> {
     if PARSE_DECIMAL_RE.is_match(s) {
         let mut offset = s.len();
         let len = s.len();
         let mut base = 1;
-        let scale_usize = usize::from(scale);
+        let scale_usize = usize::from(scale as u8);
 
         // handle the value after the '.' and meet the scale
         let delimiter_position = s.find('.');

arrow-data/src/decimal.rs

@@ -728,17 +728,17 @@ pub const MIN_DECIMAL_FOR_EACH_PRECISION: [i128; 38] = [
 pub const DECIMAL128_MAX_PRECISION: u8 = 38;
 
 /// The maximum scale for [arrow_schema::DataType::Decimal128] values
-pub const DECIMAL128_MAX_SCALE: u8 = 38;
+pub const DECIMAL128_MAX_SCALE: i8 = 38;
 
 /// The maximum precision for [arrow_schema::DataType::Decimal256] values
 pub const DECIMAL256_MAX_PRECISION: u8 = 76;
 
 /// The maximum scale for [arrow_schema::DataType::Decimal256] values
-pub const DECIMAL256_MAX_SCALE: u8 = 76;
+pub const DECIMAL256_MAX_SCALE: i8 = 76;
 
 /// The default scale for [arrow_schema::DataType::Decimal128] and
 /// [arrow_schema::DataType::Decimal256] values
-pub const DECIMAL_DEFAULT_SCALE: u8 = 10;
+pub const DECIMAL_DEFAULT_SCALE: i8 = 10;
 
 /// Validates that the specified `i128` value can be properly
 /// interpreted as a Decimal number with precision `precision`

arrow-schema/src/datatype.rs

@@ -190,14 +190,14 @@ pub enum DataType {
     /// * scale is the number of digits past the decimal
     ///
     /// For example the number 123.45 has precision 5 and scale 2.
-    Decimal128(u8, u8),
+    Decimal128(u8, i8),
     /// Exact 256-bit width decimal value with precision and scale
     ///
     /// * precision is the total number of digits
     /// * scale is the number of digits past the decimal
     ///
     /// For example the number 123.45 has precision 5 and scale 2.
-    Decimal256(u8, u8),
+    Decimal256(u8, i8),
     /// A Map is a logical nested type that is represented as
     ///
     /// `List<entries: Struct<key: K, value: V>>`

arrow-select/src/take.rs

@@ -914,7 +914,7 @@ mod tests {
         options: Option<TakeOptions>,
         expected_data: Vec<Option<i128>>,
         precision: &u8,
-        scale: &u8,
+        scale: &i8,
     ) -> Result<(), ArrowError> {
         let output = data
             .into_iter()
@@ -1032,7 +1032,7 @@ mod tests {
     fn test_take_decimal128_non_null_indices() {
         let index = UInt32Array::from(vec![0, 5, 3, 1, 4, 2]);
         let precision: u8 = 10;
-        let scale: u8 = 5;
+        let scale: i8 = 5;
         test_take_decimal_arrays(
             vec![None, Some(3), Some(5), Some(2), Some(3), None],
             &index,
@@ -1048,7 +1048,7 @@ mod tests {
     fn test_take_decimal128() {
         let index = UInt32Array::from(vec![Some(3), None, Some(1), Some(3), Some(2)]);
         let precision: u8 = 10;
-        let scale: u8 = 5;
+        let scale: i8 = 5;
         test_take_decimal_arrays(
             vec![Some(0), Some(1), Some(2), Some(3), Some(4)],
             &index,

arrow/tests/array_transform.rs

@@ -31,7 +31,7 @@ use std::sync::Arc;
 fn create_decimal_array(
     array: Vec<Option<i128>>,
     precision: u8,
-    scale: u8,
+    scale: i8,
 ) -> Decimal128Array {
     array
         .into_iter()