Like Marek Mauder in his blog post from 2009, I have run into a problem because of the different implementations of the right shift operator (shr in Pascal) in different languages.
There I was happily translating some code from Java to Object Pascal when I encountered Java's
>>> operator. A quick look at the Java docs tells me this is a logical right shift. No problem, just use shr. Next I found Java's
>> operator. This time its an arithmetic (sign preserving) right shift. Problem - no Pascal equivalent, and since operation was on signed integers I couldn't just use shr because there's a bug waiting to happen should any of the integers go negative.
Marek (above) said that replacing
a >> 1
a div 2;
worked for him.
This is fine for a single bit shift, so I thought I would see if it scaled for shifts of more than one bit. I tried dividing by 2 to the power of the number of bits to shift:
function SAR(Value: LongInt; Shift: Byte): LongInt;
Shift := Shift and 31;
if Shift = 0 then
Result := LongInt(LongWord(Value) shr Shift);
if Value < 0 then
Result := LongInt(LongWord(Result) or ($FFFFFFFF shl (32 - Shift)));
I can see several ways to optimise the function but all of them make the code less readable. So I'm not going to do the optimisations unless I have to.
I should be quite trivial to create 8, 16 and 64 bit integer overloads of the routine.