HaoYang670 commented on code in PR #1914:
URL: https://github.com/apache/arrow-rs/pull/1914#discussion_r903671741
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arrow/src/util/decimal.rs:
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@@ -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.
Review Comment:
> DecimalArray and DecimalArray already do value validation. So I skip
validation here.
Why do we need the truncation if we can always make sure that the `value`
can be stored within the precision?
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