Hello,
Skybuck presents:
KeepLowBits and KeepHighBits functions.
Visual inspection/verification program included ! ;)
// *** Begin of Code ***
program Project1;
{$APPTYPE CONSOLE}
{
Skybuck presents KeepLowBits and KeepHighBits
Version 0.01 created on 5 may 2008 by Skybuck Flying
Correct implementations this time.
Functions to keep original values could come in handy.
Visual Inspection/Verification program.
}
uses
SysUtils,
Windows;
// make overloaded versions for easy coding
// display in big endian.
procedure WriteBitPattern( const ParaByte : byte ); overload;
type
TbitRange = 0..7;
TbitSet = set of TbitRange;
var
vBit : TbitRange;
begin
for vBit:= 0 to 7 do
begin
if vBit in TbitSet(ParaByte) then
begin
write('1');
end else
begin
write('0');
end;
end;
end;
procedure WriteBitPattern( const ParaWord : word ); overload;
type
TbitRange = 0..15;
TbitSet = set of TbitRange;
var
vBit : TbitRange;
begin
for vBit:= 0 to 15 do
begin
if vBit in TbitSet(ParaWord) then
begin
write('1');
end else
begin
write('0');
end;
end;
end;
procedure WriteBitPattern( const ParaLongWord : longword ); overload;
type
TbitRange = 0..31;
TbitSet = set of TbitRange;
var
vBit : TbitRange;
begin
for vBit:= 0 to 31 do
begin
if vBit in TbitSet(ParaLongWord) then
begin
write('1');
end else
begin
write('0');
end;
end;
end;
function KeepLowBits( Value : longword; Bits : longword ) : longword;
begin
Result := Value; // 32 bits case.
if Bits <= 31 then
begin
Result := Result and not (4294967295 shl Bits); // shl instruction
limited
to 31.
end;
end;
{
8 instructions:
Project1.dpr.85: if Bits <= 31 then
00408FA4 83FA1F cmp edx,$1f
00408FA7 770B jnbe $00408fb4
Project1.dpr.87: Result := Result and not (4294967295 shl Bits); // shl
instruction limited to 31.
00408FA9 8BCA mov ecx,edx
00408FAB 83CAFF or edx,-$01
00408FAE D3E2 shl edx,cl
00408FB0 F7D2 not edx
00408FB2 23C2 and eax,edx
Project1.dpr.89: end;
00408FB4 C3 ret
}
function KeepHighBits( Value : longword; Bits : longword ) : longword;
begin
Result := Value; // 32 bits case.
if Bits <= 31 then // 0 to 31 bits case.
begin
Result := Result and not (4294967295 shr Bits); // shr instruction
limited
to 31.
end;
end;
{
8 instructions:
Project1.dpr.94: if Bits <= 31 then // 0 to 31 bits case.
00408FB8 83FA1F cmp edx,$1f
00408FBB 770B jnbe $00408fc8
Project1.dpr.96: Result := Result and not (4294967295 shr Bits); // shr
instruction limited to 31.
00408FBD 8BCA mov ecx,edx
00408FBF 83CAFF or edx,-$01
00408FC2 D3EA shr edx,cl
00408FC4 F7D2 not edx
00408FC6 23C2 and eax,edx
Project1.dpr.98: end;
00408FC8 C3 ret
}
procedure Main;
var
vValue : longword;
vBits : longword;
vResult : longword;
begin
// Test KeepHighBits
writeln('Press enter to test KeepHighBits maximum value');
readln;
// test maximum value
vValue := 4294967295;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepHighBits( vValue, vBits );
Writeln( 'KeepHighBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '21098765432109876543210987654321');
WriteBitPattern( vResult ); WriteLn;
end;
writeln('Press enter to test KeepHighBits minimum value');
readln;
// test minimum value
vValue := 0;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepHighBits( vValue, vBits );
Writeln( 'KeepHighBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '21098765432109876543210987654321');
WriteBitPattern( vResult ); WriteLn;
end;
writeln('Press enter to test KeepHighBits random value');
readln;
// test random value
vValue := GetTickCount;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepHighBits( vValue, vBits );
Writeln( 'KeepHighBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '21098765432109876543210987654321');
WriteBitPattern( vResult ); WriteLn;
end;
// Test KeepLowBits
writeln('Press enter to test KeepLowBits maximum value');
readln;
// test maximum value
vValue := 4294967295;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepLowBits( vValue, vBits );
Writeln( 'KeepLowBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '12345678901234567890123456789012');
WriteBitPattern( vResult ); WriteLn;
end;
writeln('Press enter to test KeepHighBits minimum value');
readln;
// test minimum value
vValue := 0;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepLowBits( vValue, vBits );
Writeln( 'KeepLowBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '12345678901234567890123456789012');
WriteBitPattern( vResult ); WriteLn;
end;
writeln('Press enter to test KeepHighBits random value');
readln;
// test random value
vValue := GetTickCount;
for vBits := 0 to 33 do // go over to see what happens ;) ok no problemo
begin
vResult := KeepLowBits( vValue, vBits );
Writeln( 'KeepLowBits Value: ', vValue, ' Bits: ', vBits, ' Result: ',
vResult );
WriteBitPattern( vValue ); WriteLn;
WriteLn( '12345678901234567890123456789012');
WriteBitPattern( vResult ); WriteLn;
end;
writeln('done');
end;
begin
try
Main;
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
readln;
end.
// *** End of Code ***
Bye,
Skybuck =D
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