pitrou commented on code in PR #36073: URL: https://github.com/apache/arrow/pull/36073#discussion_r1392808624
########## cpp/src/arrow/util/float16.h: ########## @@ -0,0 +1,207 @@ +// 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. + +#pragma once + +#include <array> +#include <cstdint> +#include <cstring> +#include <iosfwd> +#include <limits> +#include <type_traits> + +#include "arrow/util/endian.h" +#include "arrow/util/macros.h" +#include "arrow/util/ubsan.h" +#include "arrow/util/visibility.h" + +namespace arrow { +namespace util { + +/// \brief Class representing an IEEE half-precision float, encoded as a `uint16_t` +/// +/// The exact format is as follows (from LSB to MSB): +/// - bits 0-10: mantissa +/// - bits 10-15: exponent +/// - bit 15: sign +/// +class ARROW_EXPORT Float16 { + public: + Float16() = default; + explicit Float16(float f) : Float16(FromFloat(f)) {} + explicit Float16(double d) : Float16(FromDouble(d)) {} + template <typename T, + typename std::enable_if_t<std::is_convertible_v<T, double>>* = NULLPTR> + explicit Float16(T v) : Float16(static_cast<double>(v)) {} + + /// \brief Create a `Float16` from its exact binary representation + constexpr static Float16 FromBits(uint16_t bits) { return Float16{bits, bool{}}; } + /// \brief Create a `Float16` from a 32-bit float (may lose precision) + static Float16 FromFloat(float f); + /// \brief Create a `Float16` from a 64-bit float (may lose precision) + static Float16 FromDouble(double d); + + /// \brief Read a `Float16` from memory in native-endian byte order + static Float16 FromBytes(const uint8_t* src) { + return FromBits(SafeLoadAs<uint16_t>(src)); + } + + /// \brief Read a `Float16` from memory in little-endian byte order + static Float16 FromLittleEndian(const uint8_t* src) { + return FromBits(::arrow::bit_util::FromLittleEndian(SafeLoadAs<uint16_t>(src))); + } + + /// \brief Read a `Float16` from memory in big-endian byte order + static Float16 FromBigEndian(const uint8_t* src) { + return FromBits(::arrow::bit_util::FromBigEndian(SafeLoadAs<uint16_t>(src))); + } + + /// \brief Return the value's binary representation as a `uint16_t` + constexpr uint16_t bits() const { return bits_; } + + /// \brief Return true if the value is negative (sign bit is set) + constexpr bool signbit() const { return (bits_ & 0x8000) != 0; } + + /// \brief Return true if the value is NaN + constexpr bool is_nan() const { return (bits_ & 0x7fff) > 0x7c00; } + /// \brief Return true if the value is positive/negative infinity + constexpr bool is_infinity() const { return (bits_ & 0x7fff) == 0x7c00; } + /// \brief Return true if the value is finite and not NaN + constexpr bool is_finite() const { return (bits_ & 0x7c00) != 0x7c00; } + /// \brief Return true if the value is positive/negative zero + constexpr bool is_zero() const { return (bits_ & 0x7fff) == 0; } + + /// \brief Convert to a 32-bit float + float ToFloat() const; + /// \brief Convert to a 64-bit float + double ToDouble() const; + + explicit operator float() const { return ToFloat(); } + explicit operator double() const { return ToDouble(); } + + /// \brief Copy the value's bytes in native-endian byte order + void ToBytes(uint8_t* dest) const { std::memcpy(dest, &bits_, sizeof(bits_)); } + /// \brief Return the value's bytes in native-endian byte order + constexpr std::array<uint8_t, 2> ToBytes() const { +#if ARROW_LITTLE_ENDIAN + return ToLittleEndian(); +#else + return ToBigEndian(); +#endif + } + + /// \brief Copy the value's bytes in little-endian byte order + void ToLittleEndian(uint8_t* dest) const { + FromBits(::arrow::bit_util::ToLittleEndian(bits_)).ToBytes(dest); Review Comment: This implementation is weird, why call `FromBits` here? ```suggestion const auto bytes = ToLittleEndian(); std::memcpy(dest, bytes.data(), bytes.size()); ``` -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
