schubfach

Author: leung-ming

native/spark-expr/src/conversion_funcs/cast.rs

@@ -15,6 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use crate::conversion_funcs::schubfach;
 use crate::timezone;
 use crate::utils::array_with_timezone;
 use crate::{EvalMode, SparkError, SparkResult};
@@ -49,6 +50,7 @@ use num::{
     ToPrimitive,
 };
 use regex::Regex;
+use std::num::Saturating;
 use std::str::FromStr;
 use std::{
     any::Any,
@@ -1278,17 +1280,29 @@ where
     let input = array.as_any().downcast_ref::<PrimitiveArray<T>>().unwrap();
     let mut cast_array = PrimitiveArray::<Decimal128Type>::builder(input.len());
 
-    let mul = 10_f64.powi(scale as i32);
-
     for i in 0..input.len() {
         if input.is_null(i) {
             cast_array.append_null();
         } else {
             let input_value = input.value(i).as_();
-            let value = (input_value * mul).round().to_i128();
+            let value = schubfach::to_decimal(input_value);
 
             match value {
-                Some(v) => {
+                Some((significand, exponent)) => {
+                    let mut v = if input_value < 0. {
+                        -significand
+                    } else {
+                        significand
+                    } as i128;
+
+                    let k = exponent + scale as i32;
+                    if k > 0 {
+                        v = v.saturating_mul(Saturating(10_i128).pow(k as u32).0);
+                    } else if k < 0 {
+                        let dk = Saturating(10_i128).pow((-k) as u32).0;
+                        let (div, rem) = if dk < v { v.div_rem(&dk) } else { (0, v) };
+                        v = if rem * 2 >= dk { div + 1 } else { div };
+                    }
                     if Decimal128Type::validate_decimal_precision(v, precision).is_err() {
                         if eval_mode == EvalMode::Ansi {
                             return Err(SparkError::NumericValueOutOfRange {

native/spark-expr/src/conversion_funcs/mod.rs

@@ -16,3 +16,5 @@
 // under the License.
 
 pub mod cast;
+
+mod schubfach;