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[SR-13997] Parsing out of range Floats returns different results on macOS v Linux #56392

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spevans opened this issue Dec 27, 2020 · 7 comments
Closed

[SR-13997] Parsing out of range Floats returns different results on macOS v Linux #56392

spevans opened this issue Dec 27, 2020 · 7 comments
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@tbkka
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella

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@spevans
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spevans commented Dec 27, 2020

Previous ID SR-13997
Radar None
Original Reporter @spevans
Type Bug
Status Closed
Resolution Done
Environment

macOS 11.1 Xcode 12.3

Linux Ubuntu18.04

swift-DEVELOPMENT-SNAPSHOT-2020-12-23-a-ubuntu18.04

Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug
Assignee @tbkka
Priority Medium

md5: 739f49d3d89dfd42734adfb82130b36d

Issue Description:

When parsing a number too big to fit in a floating point type, macOS returns nil and Linux returns -inf/inf. Unfortunately the documentation is a little sparse on the expected result.

$ cat float.swift
print("Float32 1e100000", Float32("1e100000") as Any)
print("Float64 1e100000", Float64("1e100000") as Any)
print("Float80 1e100000", Float80("1e100000") as Any)

print("Float32 -1e100000", Float32("-1e100000") as Any)
print("Float64 -1e100000", Float64("-1e100000") as Any)
print("Float80 -1e100000", Float80("-1e100000") as Any)

macOS

$ swift float.swift 
Float32 1e100000 nil
Float64 1e100000 nil
Float80 1e100000 nil
Float32 -1e100000 nil
Float64 -1e100000 nil
Float80 -1e100000 nil

Linux

$ ~/swift-DEVELOPMENT-SNAPSHOT-2020-12-23-a-ubuntu18.04/usr/bin/swift float.swift 
Float32 1e100000 Optional(inf)
Float64 1e100000 Optional(inf)
Float80 1e100000 Optional(inf)
Float32 -1e100000 Optional(-inf)
Float64 -1e100000 Optional(-inf)
Float80 -1e100000 Optional(-inf)

Note however that strtod et al return the same results on macOS and Linux

$ cat double.c
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int main(int argc, char *argv[]) {

  if (argc < 2) { return 1; }
  char *endptr = NULL;
  char *number = argv[1];
  char *number_end = number + strlen(number);

  errno = 0; 
  double d = strtod(number, &endptr);
  printf("result: %f, errno: %d  pointers equal? %d *endptr = %d\n",
         d, errno, endptr == number_end, *endptr);

  return 0;
}

macOS

$ ./double 1e100000
result: inf, errno: 34  pointers equal? 1 *endptr = 0

Linux

./double 1e100000
result: inf, errno: 34  pointers equal? 1 *endptr = 0

I couldn't find anywhere in the stdlib where the errno 34 (ERANGE) was being handled to convert the result to nil on macOS.
@spevans
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spevans commented Dec 27, 2020

cc @stephentyrone

@spevans
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spevans commented Dec 27, 2020

As an extra datapoint, with {{Float16 }}there is the following odd behaviour between 1e38 and 1e39 on macOS

print(Float16("1e5"))
print(Float16("1e38"))
print(Float16("1e39"))
print(Float16("1e100"))

Xcode playgrounds:

Optional(inf)
Optional(inf)
nil
nil

Linux:

Optional(inf)
Optional(inf)
Optional(inf)
Optional(inf)

@stephentyrone
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CC @tbkka

@tbkka
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tbkka commented Dec 30, 2020

This should be fixed by #34339

Can you repeat your experiments with a recent snapshot from main?

@tbkka
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tbkka commented Dec 30, 2020

Ah. I see that you're using a recent snapshot for your Linux test (which has PR #34339) and a version of macOS that does not yet have that fix. That would explain the discrepancy you're seeing.

@tbkka
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tbkka commented Dec 30, 2020

Resolve by PR #34339

@spevans
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spevans commented Dec 30, 2020

Confirmed works ok with latest macOS snapshot. Thanks

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella
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@stephentyrone @spevans @tbkka