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[SR-2626] String to Double conversion fails on "snan" input #45231

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gribozavr opened this issue Sep 13, 2016 · 2 comments
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[SR-2626] String to Double conversion fails on "snan" input #45231

gribozavr opened this issue Sep 13, 2016 · 2 comments
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@hartbit
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. good first issue Good for newcomers standard library Area: Standard library umbrella

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@gribozavr
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Previous ID SR-2626
Radar rdar://problem/26720376
Original Reporter @gribozavr
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug, StarterBug
Assignee @hartbit
Priority Medium

md5: ba2c6f38b18ec9c711fa49aecc0453e6

Issue Description:

The string -> floating-point intializer doesn’t allow you to create signaling NaN values. In the following code, y == nil, but should have the same value as x:

let x = Double(nan: 0, signaling: true) // OK
let y = Double("snan") // nil

This relates to section 5.12.1 of IEEE 754:

Conversion of an external character sequence “snan” (regardless of case) with an optional preceding sign, to a supported format should either produce a signaling NaN or else produce a quiet NaN and signal the invalid operation exception.
@swift-ci
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Comment by W S (JIRA)

The issue seems to be with strtof_l/strtod_l/swift_strtold_l not handling "snan" while they do handle everything else ("nan", "3.5", etc...)
Perhaps "snan" can be intercepted at _swift_stdlib_strtoX_clocale_impl (there's 2, a separate one for windows, and Android seems to just call strtof_l/strtod_l/swift_strtold_l directly).
https://github.com/apple/swift/blob/master/stdlib/public/stubs/Stubs.cpp

So I was curious about when snan should signal:
could it signal just from parsing+assigning (the 'nan' would pass into a FP register)?
Is it supposed to be SIGFPE or something else? (If something else, how is it caught/recognized?)

@stephentyrone
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"snan" should produce a signaling NaN value. On some platform ABIs (i386, basically) the act of loading/storing that value may result in a signal and the value being converted to a quiet NaN. That's OK. On other platforms, it will signal invalid when it is first used in arithmetic (that's OK too!)

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@hartbit hartbit

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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. good first issue Good for newcomers standard library Area: Standard library umbrella
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