eerhardt commented on a change in pull request #9356: URL: https://github.com/apache/arrow/pull/9356#discussion_r580436711
########## File path: csharp/src/Apache.Arrow/DecimalUtility.cs ########## @@ -0,0 +1,188 @@ +// 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. + +using System; +using System.Linq; +using System.Numerics; +using System.Runtime.InteropServices; + +namespace Apache.Arrow +{ + /// <summary> + /// This is semi-optimised best attempt at converting to / from decimal and the buffers + /// </summary> + public static class DecimalUtility + { + private static readonly byte[] _minusOne = { 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255 }; + private static readonly BigInteger _maxDecimal = new BigInteger(decimal.MaxValue); + private static readonly BigInteger _minDecimal = new BigInteger(decimal.MinValue); + private static readonly ulong[] s_powersOfTen = + { + 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 10000000000, 100000000000, + 1000000000000, 10000000000000, 100000000000000, 1000000000000000, 10000000000000000, 100000000000000000, + 1000000000000000000, 10000000000000000000 + }; + private static int PowersOfTenLength => s_powersOfTen.Length - 1; + + + public static decimal GetDecimal(in ArrowBuffer valueBuffer, int index, int scale, int byteWidth, + bool isUnsigned = false) + { + int startIndex = index * byteWidth; + ReadOnlySpan<byte> value = valueBuffer.Span.Slice(startIndex, byteWidth); + BigInteger integerValue; + +#if NETCOREAPP + integerValue = new BigInteger(value); +#else + integerValue = new BigInteger(value.ToArray()); +#endif + + if (integerValue > _maxDecimal || integerValue < _minDecimal) + { + BigInteger scaleBy = BigInteger.Pow(10, scale); + BigInteger integerPart = BigInteger.DivRem(integerValue, scaleBy, out BigInteger fractionalPart); + if (integerPart > _maxDecimal || integerPart < _minDecimal) // decimal overflow, not much we can do here - C# needs a BigDecimal + { + throw new OverflowException("Value: " + integerPart + " too big or too small to be represented as a decimal"); + } + return (decimal)integerPart + DivideByScale(fractionalPart, scale); + } + else + { + return DivideByScale(integerValue, scale); + } + } + + private static decimal DivideByScale(BigInteger integerValue, int scale) + { + decimal result = (decimal)integerValue; // this cast is safe here + int drop = scale; + while (drop > PowersOfTenLength) + { + result /= s_powersOfTen[PowersOfTenLength]; + drop -= PowersOfTenLength; + } + + result /= s_powersOfTen[drop]; + return result; + } + + public static byte[] GetBytes(BigInteger integerValue, int byteWidth) + { + byte[] integerBytes = integerValue.ToByteArray(); + if (integerBytes.Length > byteWidth) + { + throw new OverflowException("Decimal size greater than " + byteWidth + " bytes: " + integerBytes.Length); + } + + if (integerBytes.Length == byteWidth) + return integerBytes; + + byte[] result = new byte[byteWidth]; + if (integerValue.Sign == -1) + { + Buffer.BlockCopy(integerBytes, 0, result, 0, integerBytes.Length); + Buffer.BlockCopy(_minusOne, 0, result, integerBytes.Length, byteWidth - integerBytes.Length); + } else Review comment: (nit) the `else` should be on a new line. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
