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AK: Add framework for a unified floating point to string conversion
Currently, the floating point to string conversion is implemented several times across the codebase. This commit provides a pretty low-level function to unify all of such conversions. It converts the given double to a fixed point decimal satisfying a few correctness criteria.
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fdc53a5995
Notes:
sideshowbarker
2024-07-17 17:38:29 +09:00
Author: https://github.com/DanShaders Commit: https://github.com/SerenityOS/serenity/commit/fdc53a5995 Pull-request: https://github.com/SerenityOS/serenity/pull/15796 Reviewed-by: https://github.com/ADKaster Reviewed-by: https://github.com/BertalanD Reviewed-by: https://github.com/Hendiadyoin1 Reviewed-by: https://github.com/davidot ✅ Reviewed-by: https://github.com/linusg
@ -16,6 +16,7 @@ set(AK_SOURCES
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StackInfo.cpp
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String.cpp
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StringBuilder.cpp
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StringFloatingPointConversions.cpp
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StringImpl.cpp
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StringUtils.cpp
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StringView.cpp
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1124
AK/StringFloatingPointConversions.cpp
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1124
AK/StringFloatingPointConversions.cpp
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File diff suppressed because it is too large
Load Diff
43
AK/StringFloatingPointConversions.h
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43
AK/StringFloatingPointConversions.h
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@ -0,0 +1,43 @@
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/*
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* Copyright (c) 2022, Dan Klishch <danilklishch@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#ifdef KERNEL
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# error This file should not be included in the KERNEL, as doubles should not appear in the \
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kernel code, although the conversion currently does not use any floating point \
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computations.
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#endif
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#include <AK/Concepts.h>
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#include <AK/Types.h>
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namespace AK {
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struct FloatingPointExponentialForm {
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bool sign;
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u64 fraction;
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i32 exponent;
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};
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/// This function finds the representation of `value' in the form of
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/// `(-1) ^ sign * fraction * 10 ^ exponent', such that (applying in the order of enumeration):
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///
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/// 1. sign is either 0 or 1, fraction is a non-negative number, exponent is an integer.
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/// 2. For +0, it is {.sign = 0, .fraction = 0, .exponent = 0},
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/// for -0, is {.sign = 1, .fraction = 0, .exponent = 0},
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/// for +inf, -inf, and NaN is undefined.
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/// 3. `(-1) ^ sign * fraction * 10 ^ exponent', computed with an infinite precision, rounds to
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/// `value' in the half to even mode.
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/// 4. len(str(fraction)) is minimal.
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/// 5. `abs((-1) ^ sign * fraction * 10 ^ exponent - value)' is minimal.
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/// 6. fraction is even.
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template<FloatingPoint T>
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FloatingPointExponentialForm convert_floating_point_to_decimal_exponential_form(T value);
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}
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using AK::convert_floating_point_to_decimal_exponential_form;
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@ -62,6 +62,7 @@ set(AK_TEST_SOURCES
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TestStack.cpp
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TestStdLibExtras.cpp
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TestString.cpp
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TestStringFloatingPointConversions.cpp
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TestStringUtils.cpp
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TestStringView.cpp
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TestTime.cpp
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74
Tests/AK/TestStringFloatingPointConversions.cpp
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74
Tests/AK/TestStringFloatingPointConversions.cpp
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@ -0,0 +1,74 @@
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/*
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* Copyright (c) 2022, Dan Klishch <danilklishch@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/BitCast.h>
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#include <AK/StringFloatingPointConversions.h>
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#include <LibTest/TestCase.h>
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static bool operator!=(AK::FloatingPointExponentialForm a, AK::FloatingPointExponentialForm b)
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{
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return a.sign != b.sign || a.exponent != b.exponent || a.fraction != b.fraction;
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}
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template<>
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struct AK::Formatter<AK::FloatingPointExponentialForm> : Formatter<FormatString> {
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ErrorOr<void> format(FormatBuilder& builder, AK::FloatingPointExponentialForm value)
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{
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return Formatter<FormatString>::format(builder, "(s={} f={} e={})"sv, value.sign, value.fraction, value.exponent);
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}
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};
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#define DOES_CONVERT_DOUBLE_TO(value, sign, fraction, exponent) \
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do { \
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EXPECT_EQ( \
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convert_floating_point_to_decimal_exponential_form(static_cast<double>(value)), \
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(AK::FloatingPointExponentialForm { sign, fraction, exponent })); \
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} while (false)
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// Tests here only check basic cases. While writing, I mostly relied on the benchmarks and
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// stress tests, which can be found at https://github.com/DanShaders/serenity-arithmetic-benchmark/blob/master/StringFloatingPointConversions.cpp .
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TEST_CASE(double_conversion)
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{
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DOES_CONVERT_DOUBLE_TO(0, 0, 0, 0);
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DOES_CONVERT_DOUBLE_TO(-0., 1, 0, 0);
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DOES_CONVERT_DOUBLE_TO(1, 0, 1, 0);
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DOES_CONVERT_DOUBLE_TO(-1, 1, 1, 0);
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DOES_CONVERT_DOUBLE_TO(.1, 0, 1, -1);
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DOES_CONVERT_DOUBLE_TO(.2, 0, 2, -1);
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DOES_CONVERT_DOUBLE_TO(.3, 0, 3, -1);
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DOES_CONVERT_DOUBLE_TO(.12345, 0, 12345, -5);
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DOES_CONVERT_DOUBLE_TO(.0012345, 0, 12345, -7);
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DOES_CONVERT_DOUBLE_TO(.1 + .2, 0, 30000000000000004, -17);
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DOES_CONVERT_DOUBLE_TO(17976931348623157e292, 0, 17976931348623157, 292);
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DOES_CONVERT_DOUBLE_TO(-17976931348623157e292, 1, 17976931348623157, 292);
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DOES_CONVERT_DOUBLE_TO(22250738585072014e-324, 0, 22250738585072014, -324);
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DOES_CONVERT_DOUBLE_TO(-22250738585072014e-324, 1, 22250738585072014, -324);
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DOES_CONVERT_DOUBLE_TO(bit_cast<double>(0xc3c04222300db8acULL), 1, 23430728857074627, 2);
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}
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#define DOES_CONVERT_FLOAT_TO(value, sign, fraction, exponent) \
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do { \
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EXPECT_EQ( \
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convert_floating_point_to_decimal_exponential_form(static_cast<float>(value)), \
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(AK::FloatingPointExponentialForm { sign, fraction, exponent })); \
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} while (false)
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TEST_CASE(float_conversion)
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{
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DOES_CONVERT_FLOAT_TO(0, 0, 0, 0);
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DOES_CONVERT_FLOAT_TO(-0., 1, 0, 0);
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DOES_CONVERT_FLOAT_TO(1, 0, 1, 0);
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DOES_CONVERT_FLOAT_TO(-1, 1, 1, 0);
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DOES_CONVERT_FLOAT_TO(.1, 0, 1, -1);
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DOES_CONVERT_FLOAT_TO(.2, 0, 2, -1);
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DOES_CONVERT_FLOAT_TO(.3, 0, 3, -1);
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DOES_CONVERT_FLOAT_TO(0.025, 0, 25, -3);
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DOES_CONVERT_FLOAT_TO(34028235e31, 0, 34028235, 31);
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DOES_CONVERT_FLOAT_TO(-34028235e31, 1, 34028235, 31);
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DOES_CONVERT_FLOAT_TO(11754944e-45, 0, 11754944, -45);
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DOES_CONVERT_FLOAT_TO(-11754944e-45, 1, 11754944, -45);
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}
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