Real.fromString on negative inf/infinity returns positive infinity #362

Version

110.99.8 (Latest)

Operating System

• Any
• Linux
• macOS
• Windows
• Other Unix

OS Version

Sequoia 15.5

Processor

• Any
• Arm (using Rosetta)
• PowerPC
• Sparc
• x86 (32-bit)
• x86-64 (64-bit)
• Other

System Component

Basis Library

Severity

Minor

Description

Real.fromString "-inf" returns SOME inf, i.e., positive infinity. It appears to only be a problem with inf/infinity parsing (e.g., in the the -nan case we get a negative sign bit).

Transcript

Testing a few combinations of [~-](inf|infinity); all of these return positive inf.

Standard ML of New Jersey [Version 110.99.8; 64-bit; April 25, 2025]
- 
- fun test x = Real.== (Real.posInf, valOf (Real.fromString x));
val test = fn : string -> bool
- 
- test "-inf"; test "~inf"; test "-infinity"; test "~infinity";
val it = true : bool
val it = true : bool
val it = true : bool
val it = true : bool

Confirming that negative nan is parsing correctly:

- Real.fromString "-nan"; Real.signBit (valOf it);
val it = SOME nan : real option
val it = true : bool
-
- Real.fromString "nan"; Real.signBit (valOf it);
val it = SOME nan : real option
val it = false : bool

Expected Behavior

Real.fromString on "-inf" and similar inputs should return SOME (~inf).

Steps to Reproduce

Please see transcript above.

Additional Information

No response

Email address

<github username> at gmail