On 1/5/06, charan raj <c.charan@xxxxxxxxx> wrote:>> I am new to this mailing list .....>> i just came across this unlikely() and likely() function in kernel code (> eg .. unlikely() is used in fork.c ) , i don;t have any idea> about what the above 2 functions does ......>> can anybody plz explain what the two functions all about .....from info gcc:
,----| -- Built-in Function: long __builtin_expect (long EXP, long C)| You may use `__builtin_expect' to provide the compiler with branch| prediction information. In general, you should prefer to use| actual profile feedback for this (`-fprofile-arcs'), as| programmers are notoriously bad at predicting how their programs| actually perform. However, there are applications in which this| data is hard to collect.|| The return value is the value of EXP, which should be an integral| expression. The value of C must be a compile-time constant. The| semantics of the built-in are that it is expected that EXP == C.| For example:|| if (__builtin_expect (x, 0))| foo ();|| would indicate that we do not expect to call `foo', since we| expect `x' to be zero. Since you are limited to integral| expressions for EXP, you should use constructions such as|| if (__builtin_expect (ptr != NULL, 1))| error ();|| when testing pointer or floating-point values.`----
kind regardsanupam��������!���W��v������ޗ��{��f���� ��ޖw�n'�������Y�����
