On 15 Aug 2007, at 03:51, mm wrote:
To J.M.
-------
You said "To be compatible with Delphi". With its current behaviour,
FPC 2.1.4 is not compatible with Delphi (and no more with FPC 2.0.4).
It is at least more compatible with Delphi than 2.1.4
You quoted the bug #8321. There, I see two problems but none concerns
the subtraction of unsigned integers.
The a, b and 256 below are all unsigned integers. a+b gets a result
type of cardinal.
1) The problem in the bug report.
"Edit1.text:=(intToStr(a + b - 256));".
Calling an overloaded function with a value whose type is not
clearly defined (a and b are bytes but 256 is not) is, at least,
dangerous programming.
Not necessarily.
2) The problem in FPC.
For some reasons, FPC decided to call IntToStr(Int64) (here, Delphi
called IntToStr(Longint)). But, instead of extending the
parameter as
a signed number, it extended it as an unsigned one. This is not
coherent. Since FPC selected a signed parameter overload, it should
have extended the parameter with
mov eax, param
cdq
not with, as it did,
mov eax, param
mov edx, 0
No. Whether you sign or zero extend depends on the "signdness" of the
source type, not of the target type. The whole point of using int64
rather than longint or dword is that it can represent all values from
low(longint) till high(cardinal) without any problem. If you "sign
extend" a cardinal into an int64, all values between high(longint)+1
and high(cardinal) are going to become negative, which is wrong.
Jonas
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