FormatFloat wrong result on macOS / FPC trunk
Summary
SysUtils FormatFloat function produces zeros irrespective of the passed value (FPC trunk / macOS).
It does work correctly with FPC 3.2.2 on the very same machine.
Also works fine on Linux/amd64 FPC trunk.
System Information
- Operating system: macOS Sequoia 15.3.1
- Processor architecture: AARCH64 (Apple M2)
- Compiler version: Free Pascal Compiler version 3.3.1-17610-gd91be468da [2025/03/07] for aarch64
- Device: MacBook Air
Steps to reproduce
program FFloat;
uses
SysUtils;
begin
WriteLn(FormatFloat('#.##', 3.1416));
end.Example Project
https://gist.github.com/olatov/747c6e32b23c11de4b8fcb02f30b8f2e
What is the current bug behavior?
Prints 0.00
What is the expected (correct) behavior?
Prints 3.14
Possible fixes
The debugger got me to this line
and it looks like the PChar cast mangles Value somehow. I've no idea how though.
It has something to do with TFormatSettings record passed to FloatToTextFmt underline call. I can see this invokes Move procedure (alias FPC_MOVE) - copying to the procedure's stack, I assume? So on most platforms FPC has the implementation in assembly, though in macOS/aarch64 it's delegated to external clib name 'bcopy'. Which is either doing not exactly what's needed - or perhaps is called incorrectly.