Two Tricks of Delphi

Two tricks of making integer computation faster in Delphi.

1. Two integers a and b, to compute a mod b, where b is power of two (two, four, eight ... etc)...

in delphi, you write
result := a mod b;
in this case, to make it faster,
you can write
result := a and (b - 1); // b >= 2, and power of 2.

2. Two integers a (a >= 0) and b, to compute a div b, where b is power of two (two, four, eight ... etc)...

in delphi, you write
result := a div b;
in this case, to make it faster,
you can write
c := fun(b); // fun returns the integer(log2(b))
result := a shr c; // where b >= 2, and power of 2

// returns the left-most significant digit.
function fun(b: integer): integer; assembler; register;
asm
bsr eax, eax
end;

if (a < 0), it can be reworked as result = -((-a) shr c)