There was an error in the code i supplied; the variable 'i' obviously
has to be integer as corrected below. I show another routine (IsZero2)
which is pretty much as I would have coded without any input. I couldn't
hazard a guess as to which routine is faster.
Francois Piette suggested using assembler eg. the SCAS instruction with
REP prefix. This would certainly be the fastest on a 486 but AFIR, when
the Pentium arrived it turned out that coding the loop 'manually' was
faster.
Sorry about the error. I'm away the rest of the week and so have
/really/ terminated:-)
-malcolm
function IsZero(const AddrOfDataToSearch:Pointer; const
LengthInBytes:cardinal) : boolean;
var
p:pLongWord; //pLongWord is defined System unit in D7
i:integer;
begin
p:=pLongWord(AddrOfDataToSearch);
result:=false;
for i:=0 to ((LengthInBytes div 4)-1) do
if p^ <> 0 then
exit
else
inc(p);
case LengthInBytes mod 4 of
0: result:=true;
1: if pByte(p)^=0 then result:=true;
2: if pWord(p)^=0 then result:=true;
3: if ((pWord(p)^=0) and (PByte(LongWord(p)+2)^=0)) then result:=true;
end;
end;//IsZero
(*
;p:=pLongWord(AddrOfDataToSearch);
mov [esp],eax
;result:=false;
xor ecx,ecx
;for i:=0 to ((LengthInBytes div 4)-1) do
mov eax,edx
shr eax,2
dec eax
test eax,eax
jb $2
inc eax
;if p^ <> 0 then exit
$1 mov ebx,[esp]
cmp dword ptr [ebx],0
jnz exit
;inc(p);
add dword ptr [esp], 4
;for i:=0 to ((LengthInBytes div 4)-1) do
dec eax
jnz $1
$2
*)
function IsZero2(const AddrOfDataToSearch:Pointer; const
LengthInBytes:cardinal) : boolean;
var
p,pend:pLongWord; //pLongWord is defined System unit in D7
begin
p:=pLongWord(AddrOfDataToSearch);
LongWord(pend):=LongWord(p)+LengthInBytes div 4 * 4;
//This is probably faster but is less transparent:
//LongWord(pend):=LongWord(p)+LengthInBytes and not 3;
result:=false;
while LongWord(p)<LongWord(pend) do
if p^ <> 0 then
exit
else
inc(p);
case LengthInBytes mod 4 of
0: result:=true;
1: if pByte(p)^=0 then result:=true;
2: if pWord(p)^=0 then result:=true;
3: if ((pWord(p)^=0) and (PByte(LongWord(p)+2)^=0)) then result:=true;
end;
end;//IsZero2
(*
;p:=pLongWord(AddrOfDataToSearch);
mov [esi],eax
;LongWord(pend):=LongWord(p)+LengthInBytes div 4 * 4;
mov ecx,edx
shr ecx,2
shl ecx,2
add ecx,[esi]
mov eax,ecx
;result:=false;
xor ecx,ecx
jmp @2
;if p^ <> 0 then exit
@1 mov ebx,[esi]
cmp dword ptr [ebx],0
jnz exit
;inc(p);
add dword ptr [esi],4
;while LongWord(p)<LongWord(pend) do
@2 mov ebx,[esi]
cmp ebx,eax
jb @1
*)
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