alamb commented on code in PR #1914:
URL: https://github.com/apache/arrow-rs/pull/1914#discussion_r903732256
##########
arrow/src/util/decimal.rs:
##########
@@ -17,109 +17,201 @@
//! Decimal related utils
-use std::cmp::Ordering;
+use crate::error::{ArrowError, Result};
+use num::bigint::BigInt;
+use std::cmp::{min, Ordering};
+
+pub trait BasicDecimal: PartialOrd + Ord + PartialEq + Eq {
+ /// The bit-width of the internal representation.
+ const BIT_WIDTH: usize;
+
+ /// Tries to create a decimal value from precision, scale and bytes.
+ /// If the length of bytes isn't same as the bit width of this decimal,
+ /// returning an error. The bytes should be stored in little-endian order.
+ ///
+ /// Safety:
+ /// This method doesn't validate if the decimal value represented by the
bytes
+ /// can be fitted into the specified precision.
+ fn try_new_from_bytes(precision: usize, scale: usize, bytes: &[u8]) ->
Result<Self>
+ where
+ Self: Sized,
+ {
+ if precision < scale {
+ return Err(ArrowError::InvalidArgumentError(format!(
+ "Precision {} is less than scale {}",
+ precision, scale
+ )));
+ }
+
+ if bytes.len() == Self::BIT_WIDTH / 8 {
+ Ok(Self::new(precision, scale, bytes))
+ } else {
+ Err(ArrowError::InvalidArgumentError(format!(
+ "Input to Decimal{} must be {} bytes",
+ Self::BIT_WIDTH,
+ Self::BIT_WIDTH / 8
+ )))
+ }
+ }
+
+ /// Creates a decimal value from precision, scale, and bytes.
+ ///
+ /// Safety:
+ /// This method doesn't check if the length of bytes is compatible with
this decimal.
+ /// Use `try_new_from_bytes` for safe constructor.
+ fn new(precision: usize, scale: usize, bytes: &[u8]) -> Self;
+
+ /// Returns the raw bytes of the integer representation of the decimal.
+ fn raw_value(&self) -> &[u8];
+
+ /// Returns the precision of the decimal.
+ fn precision(&self) -> usize;
+
+ /// Returns the scale of the decimal.
+ fn scale(&self) -> usize;
+
+ /// Returns the string representation of the decimal.
+ /// If the string representation cannot be fitted with the precision of
the decimal,
+ /// the string will be truncated.
+ fn as_string(&self) -> String {
Review Comment:
```suggestion
fn to_string(&self) -> String {
```
I think `to` is a more rust idomatic name -- functions with `as_*` names are
typically used for cheap conversions
##########
arrow/src/util/decimal.rs:
##########
@@ -131,10 +223,60 @@ mod tests {
}
#[test]
- fn decimal_128_from_bytes() {
+ fn decimal_invalid_precision_scale() {
let bytes = 100_i128.to_le_bytes();
- let value = Decimal128::new_from_bytes(5, 2, &bytes);
+ let err = Decimal128::try_new_from_bytes(5, 6, &bytes);
+ assert!(err.is_err());
+ }
+
+ #[test]
+ fn decimal_128_from_bytes() {
+ let mut bytes = 100_i128.to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(5, 2, &bytes).unwrap();
assert_eq!(value.as_string(), "1.00");
+
+ bytes = (-1_i128).to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(5, 2, &bytes).unwrap();
+ assert_eq!(value.as_string(), "-0.01");
+
+ bytes = i128::MAX.to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(38, 2, &bytes).unwrap();
+ assert_eq!(value.as_string(),
"170141183460469231731687303715884105.72");
+
+ bytes = i128::MIN.to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(38, 2, &bytes).unwrap();
+ assert_eq!(
+ value.as_string(),
+ "-170141183460469231731687303715884105.72"
+ );
+
+ // Truncated
+ bytes = 12345_i128.to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(3, 2, &bytes).unwrap();
+ assert_eq!(value.as_string(), "1.23");
+
+ bytes = (-12345_i128).to_le_bytes();
+ let value = Decimal128::try_new_from_bytes(3, 2, &bytes).unwrap();
+ assert_eq!(value.as_string(), "-1.23");
+ }
+
+ #[test]
+ fn decimal_256_from_bytes() {
+ let mut bytes = vec![0; 32];
+ bytes[0..16].clone_from_slice(&100_i128.to_le_bytes());
+ let value = Decimal256::try_new_from_bytes(5, 2,
bytes.as_slice()).unwrap();
+ assert_eq!(value.as_string(), "1.00");
+
+ bytes[0..16].clone_from_slice(&i128::MAX.to_le_bytes());
Review Comment:
it would be nice to check at least one value that is larger and one that is
smaller than would fit in `i128`
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