如何使用Delphi 6做到这一点?UInt64在Delphi 6中是未知的。它在后来的版本中被引入。
var
i, j: Int64;
if UInt64(i) < UInt64(j) then ...
I am thinking of an asm procedure.
function UInt64CompareLT(i, j: Int64): Boolean;
asm
???
end;
function UInt64CompareGT(i, j: Int64): Boolean;
asm
???
end;
SysUtils
中的Int64Rec
类型是为挑选64位整数的部分而设计的。
如果你碰巧使用的是一个早于这种类型的Delphi,请自己定义它:
type
Int64Rec = packed record
case Integer of
0: (Lo, Hi: Cardinal);
1: (Cardinals: array [0..1] of Cardinal);
2: (Words: array [0..3] of Word);
3: (Bytes: array [0..7] of Byte);
end;
更重要的是,您只需要一个返回-1表示小于,1表示大于,0表示等于的函数。类似这样的东西:
function CompareUInt64(const i, j: Int64): Integer;
begin
if Int64Rec(i).Hi < Int64Rec(j).Hi then
Result := -1
else if Int64Rec(i).Hi > Int64Rec(j).Hi then
Result := 1
else if Int64Rec(i).Lo < Int64Rec(j).Lo then
Result := -1
else if Int64Rec(i).Lo > Int64Rec(j).Lo then
Result := 1
else
Result := 0;
end;
这个想法是,你首先比较高阶部分,只有当它相等时,你才能继续比较低阶部分。
这可以通过Cardinal
的比较函数而变得更简单。
function CompareCardinal(const i, j: Cardinal): Integer;
begin
if i < j then
Result := -1
else if i > j then
Result := 1
else
Result := 0;
end;
function CompareUInt64(const i, j: Int64): Integer;
begin
Result := CompareCardinal(Int64Rec(i).Hi, Int64Rec(j).Hi);
if Result = 0 then
Result := CompareCardinal(Int64Rec(i).Lo, Int64Rec(j).Lo);
end;
最后,如果您需要问题的布尔函数,它们可以在这个更通用的函数之上实现。
没有必要使用汇编程序(但是,当然,你可以这样做):你可以比较Int64的高低部分:
function UInt64CompareLT(i, j: Int64): Boolean;
begin
if (LongWord(i shr 32) < LongWord(j shr 32)) then
Result := true
else if (LongWord(i shr 32) > LongWord(j shr 32)) then
Result := false
else if (LongWord(i and $FFFFFFFF) < LongWord(j and $FFFFFFFF)) then
Result := true
else
Result := false;
end;
function UInt64CompareGT(i, j: Int64): Boolean;
begin
if (LongWord(i shr 32) > LongWord(j shr 32)) then
Result := true
else if (LongWord(i shr 32) < LongWord(j shr 32)) then
Result := false
else if (LongWord(i and $FFFFFFFF) > LongWord(j and $FFFFFFFF)) then
Result := true
else
Result := false;
end;
使用汇编程序是可能的,但会将代码绑定到特定的机器体系结构
你可以在纯Pascal中实现这一点,如下所示:
type
//Delcare a variant record to have 2 ways to access the same data in memory.
T64Bit = record
case Integer of
0: (I64: Int64;);
1: (Small: Cardinal; Big: Cardinal);
end;
var
I, J: T64Bit;
begin
//You can set the value via normal Int64 assignment as follows:
I.I64 := 1;
J.I64 := 2;
//Then you can compare the "big" and "small" parts on the number using
//unsigned 32-bit comparisons as follows.
if (I.Big < J.Big) or ((I.Big = J.Big) and (I.Small< J.Small)) then
//The logic is as follows...
// If the big part is less than, the the small part doesn't matter
// If the big parts are equal, then the comparison of the small parts determines the result.