tustvold commented on code in PR #3139:
URL: https://github.com/apache/arrow-rs/pull/3139#discussion_r1028299154
##########
arrow-cast/src/cast.rs:
##########
@@ -1955,12 +1956,26 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1:
usize, const BYTE_WIDTH2: usi
// For example, input_scale is 4 and output_scale is 3;
// Original value is 11234_i128, and will be cast to 1123_i128.
let div = 10_i128.pow((input_scale - output_scale) as u32);
+ let half = div / 2;
+ let neg_half = half.neg();
if BYTE_WIDTH1 == 16 {
let array =
array.as_any().downcast_ref::<Decimal128Array>().unwrap();
if BYTE_WIDTH2 == 16 {
- let iter = array
- .iter()
- .map(|v| v.and_then(|v| v.div_checked(div).ok()));
+ // rounding the result
+ let iter = array.iter().map(|v| {
+ v.map(|v| {
+ // the div must be gt_eq 10, we don't need to check
the overflow for the `div`/`mod` operation
+ let d = v / div;
+ let r = v % div;
Review Comment:
```suggestion
let d = v.wrapping_div(div);
let r = v.wrapping_rem(div);
```
##########
arrow-cast/src/cast.rs:
##########
@@ -1955,12 +1956,26 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1:
usize, const BYTE_WIDTH2: usi
// For example, input_scale is 4 and output_scale is 3;
// Original value is 11234_i128, and will be cast to 1123_i128.
let div = 10_i128.pow((input_scale - output_scale) as u32);
+ let half = div / 2;
+ let neg_half = half.neg();
Review Comment:
```suggestion
let neg_half = half.wrapping_neg();
```
As we've divided by 2 this can't overflow
##########
arrow-cast/src/cast.rs:
##########
@@ -1955,12 +1956,26 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1:
usize, const BYTE_WIDTH2: usi
// For example, input_scale is 4 and output_scale is 3;
// Original value is 11234_i128, and will be cast to 1123_i128.
let div = 10_i128.pow((input_scale - output_scale) as u32);
+ let half = div / 2;
+ let neg_half = half.neg();
if BYTE_WIDTH1 == 16 {
let array =
array.as_any().downcast_ref::<Decimal128Array>().unwrap();
if BYTE_WIDTH2 == 16 {
- let iter = array
- .iter()
- .map(|v| v.and_then(|v| v.div_checked(div).ok()));
+ // rounding the result
+ let iter = array.iter().map(|v| {
+ v.map(|v| {
+ // the div must be gt_eq 10, we don't need to check
the overflow for the `div`/`mod` operation
+ let d = v / div;
+ let r = v % div;
+ if v >= 0 && r >= half {
+ d + 1
Review Comment:
```suggestion
d.wrapping_add(1)
```
##########
arrow-cast/src/cast.rs:
##########
@@ -1955,12 +1956,26 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1:
usize, const BYTE_WIDTH2: usi
// For example, input_scale is 4 and output_scale is 3;
// Original value is 11234_i128, and will be cast to 1123_i128.
let div = 10_i128.pow((input_scale - output_scale) as u32);
+ let half = div / 2;
+ let neg_half = half.neg();
if BYTE_WIDTH1 == 16 {
let array =
array.as_any().downcast_ref::<Decimal128Array>().unwrap();
if BYTE_WIDTH2 == 16 {
- let iter = array
- .iter()
- .map(|v| v.and_then(|v| v.div_checked(div).ok()));
+ // rounding the result
+ let iter = array.iter().map(|v| {
+ v.map(|v| {
+ // the div must be gt_eq 10, we don't need to check
the overflow for the `div`/`mod` operation
+ let d = v / div;
+ let r = v % div;
+ if v >= 0 && r >= half {
+ d + 1
+ } else if v < 0 && r <= neg_half {
+ d - 1
Review Comment:
```suggestion
d.wrapping_sub(1)
```
##########
arrow-cast/src/cast.rs:
##########
@@ -1981,9 +2006,23 @@ fn cast_decimal_to_decimal_safe<const BYTE_WIDTH1:
usize, const BYTE_WIDTH2: usi
} else {
let array =
array.as_any().downcast_ref::<Decimal256Array>().unwrap();
let div = i256::from_i128(div);
+ let half = div / i256::from_i128(2);
+ // TODO: it's better to implement the neg
+ let neg_half = half * i256::from_i128(-1);
Review Comment:
```suggestion
let neg_half = half.wrapping_neg();
```
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