parthchandra commented on code in PR #3619: URL: https://github.com/apache/datafusion-comet/pull/3619#discussion_r2897212225
########## native/spark-expr/src/math_funcs/wide_decimal_binary_expr.rs: ########## @@ -0,0 +1,502 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +//! Fused wide-decimal binary expression for Decimal128 add/sub/mul that may overflow. +//! +//! Instead of building a 4-node expression tree (Cast→BinaryExpr→Cast→Cast), this performs +//! i256 intermediate arithmetic in a single expression, producing only one output array. + +use crate::math_funcs::utils::get_precision_scale; +use crate::EvalMode; +use arrow::array::{Array, ArrayRef, AsArray, Decimal128Array}; +use arrow::datatypes::{i256, DataType, Decimal128Type, Schema}; +use arrow::error::ArrowError; +use arrow::record_batch::RecordBatch; +use datafusion::common::Result; +use datafusion::logical_expr::ColumnarValue; +use datafusion::physical_expr::PhysicalExpr; +use std::fmt::{Display, Formatter}; +use std::hash::Hash; +use std::{any::Any, sync::Arc}; + +/// The arithmetic operation to perform. +#[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)] +pub enum WideDecimalOp { + Add, + Subtract, + Multiply, +} + +impl Display for WideDecimalOp { + fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result { + match self { + WideDecimalOp::Add => write!(f, "+"), + WideDecimalOp::Subtract => write!(f, "-"), + WideDecimalOp::Multiply => write!(f, "*"), + } + } +} + +/// A fused expression that evaluates Decimal128 add/sub/mul using i256 intermediate arithmetic, +/// applies scale adjustment with HALF_UP rounding, checks precision bounds, and outputs +/// a single Decimal128 array. +#[derive(Debug, Eq)] +pub struct WideDecimalBinaryExpr { + left: Arc<dyn PhysicalExpr>, + right: Arc<dyn PhysicalExpr>, + op: WideDecimalOp, + output_precision: u8, + output_scale: i8, + eval_mode: EvalMode, +} + +impl Hash for WideDecimalBinaryExpr { + fn hash<H: std::hash::Hasher>(&self, state: &mut H) { + self.left.hash(state); + self.right.hash(state); + self.op.hash(state); + self.output_precision.hash(state); + self.output_scale.hash(state); + self.eval_mode.hash(state); + } +} + +impl PartialEq for WideDecimalBinaryExpr { + fn eq(&self, other: &Self) -> bool { + self.left.eq(&other.left) + && self.right.eq(&other.right) + && self.op == other.op + && self.output_precision == other.output_precision + && self.output_scale == other.output_scale + && self.eval_mode == other.eval_mode + } +} + +impl WideDecimalBinaryExpr { + pub fn new( + left: Arc<dyn PhysicalExpr>, + right: Arc<dyn PhysicalExpr>, + op: WideDecimalOp, + output_precision: u8, + output_scale: i8, + eval_mode: EvalMode, + ) -> Self { + Self { + left, + right, + op, + output_precision, + output_scale, + eval_mode, + } + } +} + +impl Display for WideDecimalBinaryExpr { + fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result { + write!( + f, + "WideDecimalBinaryExpr [{} {} {}, output: Decimal128({}, {})]", + self.left, self.op, self.right, self.output_precision, self.output_scale + ) + } +} + +/// Compute `value / divisor` with HALF_UP rounding. +#[inline] +fn div_round_half_up(value: i256, divisor: i256) -> i256 { + let (quot, rem) = (value / divisor, value % divisor); + // HALF_UP: if |remainder| * 2 >= |divisor|, round away from zero + let abs_rem_x2 = if rem < i256::ZERO { + rem.wrapping_neg() + } else { + rem + } + .wrapping_mul(i256::from_i128(2)); + let abs_divisor = if divisor < i256::ZERO { + divisor.wrapping_neg() + } else { + divisor + }; + if abs_rem_x2 >= abs_divisor { + if (value < i256::ZERO) != (divisor < i256::ZERO) { + quot.wrapping_sub(i256::ONE) + } else { + quot.wrapping_add(i256::ONE) + } + } else { + quot + } +} + +/// i256 constant for 10. +const I256_TEN: i256 = i256::from_i128(10); + +/// Compute 10^exp as i256. +#[inline] +fn i256_pow10(exp: u32) -> i256 { + let mut result = i256::ONE; + for _ in 0..exp { + result = result.wrapping_mul(I256_TEN); + } + result +} + +/// Maximum i128 value for a given decimal precision (1-indexed). +/// precision p allows values in [-10^p + 1, 10^p - 1]. +#[inline] +fn max_for_precision(precision: u8) -> i256 { + i256_pow10(precision as u32).wrapping_sub(i256::ONE) +} + +impl PhysicalExpr for WideDecimalBinaryExpr { + fn as_any(&self) -> &dyn Any { + self + } + + fn data_type(&self, _input_schema: &Schema) -> Result<DataType> { + Ok(DataType::Decimal128( + self.output_precision, + self.output_scale, + )) + } + + fn nullable(&self, _input_schema: &Schema) -> Result<bool> { + Ok(true) + } + + fn evaluate(&self, batch: &RecordBatch) -> Result<ColumnarValue> { + let left_val = self.left.evaluate(batch)?; + let right_val = self.right.evaluate(batch)?; + + let (left_arr, right_arr): (ArrayRef, ArrayRef) = match (&left_val, &right_val) { + (ColumnarValue::Array(l), ColumnarValue::Array(r)) => (Arc::clone(l), Arc::clone(r)), + (ColumnarValue::Scalar(l), ColumnarValue::Array(r)) => { + (l.to_array_of_size(r.len())?, Arc::clone(r)) + } + (ColumnarValue::Array(l), ColumnarValue::Scalar(r)) => { + (Arc::clone(l), r.to_array_of_size(l.len())?) + } + (ColumnarValue::Scalar(l), ColumnarValue::Scalar(r)) => (l.to_array()?, r.to_array()?), + }; + + let left = left_arr.as_primitive::<Decimal128Type>(); + let right = right_arr.as_primitive::<Decimal128Type>(); + let (_p1, s1) = get_precision_scale(left.data_type()); + let (_p2, s2) = get_precision_scale(right.data_type()); + + let p_out = self.output_precision; + let s_out = self.output_scale; + let op = self.op; + let eval_mode = self.eval_mode; + + let bound = max_for_precision(p_out); + let neg_bound = i256::ZERO.wrapping_sub(bound); + + let result: Decimal128Array = match op { + WideDecimalOp::Add | WideDecimalOp::Subtract => { + let max_scale = std::cmp::max(s1, s2); + let l_scale_up = i256_pow10((max_scale - s1) as u32); + let r_scale_up = i256_pow10((max_scale - s2) as u32); + let need_rescale = s_out < max_scale; + let rescale_divisor = if need_rescale { + i256_pow10((max_scale - s_out) as u32) + } else { + i256::ONE Review Comment: @andygrove did you miss this comment? -- This is an automated message from the Apache Git Service. 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