Trunc(log2(n))

之前一直是Trunc(ln(n)/ln(2))做，今天做uva时一直wa，一直wa……发现精度问题很重要啊。

11591561	11714	Blind Sorting	Accepted	PASCAL	0.076	2013-04-11 13:00:25
11591467	11714	Blind Sorting	Wrong answer	PASCAL	0.068	2013-04-11 12:42:31
11591418	11714	Blind Sorting	Wrong answer	PASCAL	0.364	2013-04-11 12:33:54

用这样的写法勉强过了，求交流更好的写法

Function log2(P:cardinal):cardinal;inline;
var
 i:longint;
  begin
  for i:=31 downto 0 do
    if (1 shl i) and p>0 then exit(i);
end;

 更好的写法

Function log2(P:longint):longint;inline;
var
 k:real;
  begin
  k:=ln(n)/ln(2);
  if round(k)-k<1e-4 then exit(round(k)) else exit(trunc(k));
end;