Floating-point parsing and formatting improvements in .net core 3.0 .net blog v lab electricity


The primary goals of this work were to ensure correctness and standards compliance with IEEE 754-2008. For those unfamiliar with the standard, it defines the underlying format, base operations, and behaviors for binary floating-point types such as System.Single ( float) and System.Double ( double). The majority of modern processors and programming languages support some version of this standard, so it is important to ensure it is implemented correctly. The standard does not impact the integer types, such as System.Int32 ( int), nor does it impact the other floating-point types, such as System.Decimal ( decimal). Initial Work

We started with gas in oil parsing changes, as part of the .NET Core 2.1 release. Initially, this was just an attempt to fix a perf difference between Windows and Unix and was done by @mazong1123 in dotnet/coreclr#12894, which implements the Dragon4 algorithm. @mazong1123 also made a follow up PR which improved perf even more by implementing the Grisu3 algorithm in dotnet/coreclr#14646. However, in reviewing the code we determined that existing infrastructure had a number of issues that prevented us from always doing the right thing and that it would require significantly more work to make correct. Porting to C#

The first step in fixing austin electricity outage these underlying infrastructure issues was porting the code from native to managed. We did this work in dotnet/coreclr#19999 and dotnet/coreclr#20080. The result was we made the code more portable, allowed it to be shared with the other frameworks/runtimes (such as Mono and CoreRT), made it possible to easily debug the code with the .NET Debugger, and made it available through SourceLink. Making the parser IEEE compliant

To elaborate, every floating-point value requires between 1 and X significant digits (i.e. all digits that are not leading or trailing zeros) in order to roundtrip the value (that is, in order for double.Parse(value.ToString()) to return exactly value). This is at most 17 digits for double and at most 9 digits for float. However, this only applies to strings that are first formatted from an existing floating-point value. When parsing from an arbitrary string, you may have to instead consider up to Y digits to ensure that you produce the “nearest” representable value. This is 768 digits for double a level physics electricity equations and 113 digits for float. We have tests validating such strings parse correctly in RealParserTestsBase.netcoreapp.cs and dotnet/corefx#35701. More details on this can be found on Rick Regan’s Exploring Binary blog.

An example of such a string would be for double.Epsilon (which is the smallest value that is greater than zero). The shortest roundtrippable string for this value is only 5e-324, but the exact string (i.e. the string that contains all significant digits available in the underlying value) for this value is exactly 1074 digits long, which is comprised of 323 leading zeros and 751 significant digits. You then need one additional digit zyklon b gas effects to ensure that the string is rounded in the correct direction (should it be exactly double.Epsilon or the smallest value that is greater than double.Epsilon).

• ToString(), ToString(G), and ToString(R) will now return the shortest roundtrippable string. This ensures that users end up with something that just works by default. An example of where it was problematic was Math.PI.ToString() where the string that was previously being returned (for ToString() and ToString(G)) was 3.14159265358979; instead, it should have returned 3.1415926535897931. The previous result, when parsed, returned a value which was internally off by 7 ULP (units in last place) from the actual value of Math.PI. This meant that it was very easy for users to get into a scenario where they would accidentally lose some precision on a floating-point value when the needed to serialize/deserialize it.

• For the G format specifier that takes a precision (e.g. G3), the precision specifier electricity in the 1920s is now always respected. For double with precisions less than 15 (inclusive) and for float with precisions less than 6 (inclusive) this means you get the same string as before. For precisions greater than that, you will get up to that many significant digits, provided those digits are available (i.e. (1.0).ToString(G17) will still return 1 since the exact string only has one significant digit; but Math.PI.ToString(G20) will now return 3.141592653589793116, since the exact string contains at least 20 significant digits).

• For the C, E, F, N, and P format specifiers the changes are similar. The difference is that these format specifiers treat the precision as the number of digits after the decimal point, in contrast to G which treats it as the number of significant digits. The previous implementation had a bug where, for strings that contained more than 15 significant digits, it would actually fill in the remaining digits with zero, regardless of whether they appeared before or after the decimal gas pain relief point. As an example, (1844674407370955.25).ToString(F4)would previously return 1844674407370960.0000. The exact string, however, actually contains enough information to fill all the integral digits. With the changes made we instead fill out the available integral digits while still respecting the request for the 4 digits after the decimal point and instead return 1844674407370955.2500.

When picking up .NET Core 3.0, it is expected that you may encounter some of the differences described in this post in your application or library code. The general recommendation is that the e85 gasoline code be updated to handle these changes. However, this may not be possible in all cases and a workaround may be required. Focused testing for floating-point specific code is recommended.

For differences in parsing, there is no mechanism to fallback to the old behavior. There were already differences across various operating systems (i.e. Linux, Windows, macOS, etc) and architectures (i.e. x86, x64, ARM, ARM64, etc). The new logic makes all of these consistent and ensures that the result returned is consistent with the corresponding language literal.

• For the remaining format-specifiers that take a precision ( C, E, F, N, and P), there is no mechanism to fallback to the old behavior. The previous behavior would clamp precisions greater than 14 (exclusive) to be 17 for E and 15 for the others. However, this only impacted the significant digits that would be displayed, the remaining digits (even if available) would be filled in as zero.