Optimization of TextToFloat

Summary

The function TextToFloat() is the internal basis of the String-to-Float conversions of FPC, such as StrToFloat or TryStrToFloat. The function can be optimized at two places:

• At the beginning of the routine there is a conversion from PChar to string which in most cases is not necessary because the argument passed to StrToFloat, TryStrToFloat etc. already is a string. (#1)
• There are three calls to pos() in order to correctly handle the decimal and thousand separators. At least the last one which replaces the decimal separator in the string by a dot can be omitted if the FormatSettings.DecimalSeparator already is a dot. (#2)

Here is the original code:

Function TextToFloat(Buffer: PChar; Out Value: Extended; Const FormatSettings: TFormatSettings): Boolean;
Var
  S : String;
...
Begin
  S:=StrPas(Buffer);         // #1
  ...
  P:=Pos(FormatSettings.DecimalSeparator,S);    // #2
  If (P<>0) Then                
    S[P] := '.';

System Information

• Operating system: Win-11 (64 bit)
• Processor architecture: x86-64
• Compiler version: FPC/main (e01da240)
• Device: Computer

Fix

The attached patch fixes the issue:

texttofloat.diff

#1: It moves the current code of TextToFloat() (there are two overloaded variants) into new procedures InternalTextToFloat() having a string argument rather than the PChar as in the old code. The call to StrPas(Buffer), therefore, can be removed. In order to maintain compatibility of the interface, TextToFloat() is kept with the PChar argument, but it just calls InternalTextToFloat after doing the conversion to string here.

#2: The unnecessary call to pos() is avoided by putting this code into an if FormatSettings.DecimalSeparator <> '.' block.

A test project is added which verifies that nothing breaks with these changes. It also includes a simple speed test which demonstrates that the patch results in a 20% speed improvement (when the decimal separator is a point).

• execution time before: 1.21 seconds
• execution time after: 0.97 seconds, i.e. 20% faster.

texttofloat.zip