Category 

Modifiers, Keyword extensions 

Syntax  

return-value _fastcall function-name(parm-list)
return-value __fastcall function-name(parm-list)

Description 

Use the __fastcall modifier to declare functions that expect parameters to be passed in registers. The first three parameters are passed (from left to right) in EAX, EDX, and ECX, if they fit in the register. The registers are not used if the parameter is a floating-point or struct type.

Functions declared using _cdecl or _pascal cannot have the _fastcall modifier because they use the stack to pass parameters. Likewise, the __fastcall modifier cannot be used together with _export. 

The compiler prefixes the __fastcall function name with an at-sign ("@"). This prefix applies to both unmangled C function names and to mangled C++ function names. 

For Microsoft C++ style __fastcall implementation, see __msfastcall and __msreturn.