On Tuesday 03 June 2008, Harvey Harrison wrote: > On Tue, 2008-06-03 at 22:45 +0200, Ivo van Doorn wrote: > > By using __ffs() the register offsets were always calculated > > at run-time which all FIELD32/FIELD16 definitions were builtin > > constants. This means we can heavily optimize the register handling > > by allowing GCC to do all the work during compilation. > > > > Add some compile_ffs() macros to perform the calculation at > > compile time. After this each rt2x00 module size is reduced > > by ~2500 bytes. And the stack size of several functions is reduced > > as well which further limits the number of rt2x00 results in > > 'make checkstack'. > > +/* > > + * Macro's to find first set bit in a variable. > > + * These macro's behaves the same as the __ffs() function with > > + * the most important difference that this is done during > > + * compile-time rather then run-time. > > + */ > > #define const_ffs8(__x) ( \ > BUILD_BUG_ON(!__builtin_constant_p(__x)); \ > __builtin_choose_expr((__x) & 0x01, 0, \ > __builtin_choose_expr((__x) & 0x02, 1, \ > __builtin_choose_expr((__x) & 0x04, 2, \ > __builtin_choose_expr((__x) & 0x08, 3, \ > __builtin_choose_expr((__x) & 0x10, 4, \ > __builtin_choose_expr((__x) & 0x20, 5, \ > __builtin_choose_expr((__x) & 0x40, 6, \ > __builtin_choose_expr((__x) & 0x80, 7, \ > 8)))))))); ) > > #define const_ffs16(__x) ( \ > __builtin_choose_expr((__x) & 0xff, \ > const_ffs8(__x), \ > const_ffs8((__x) >> 8) + 8); ) > > > #define const_ffs32(__x) ( \ > __builtin_choose_expr((__x) & 0xffff, \ > const_ffs16(__x), \ > const_ffs16((__x) >> 16) + 16); ) > > > Just a thought. Thanks for the tipe, that does sound a lot cleaner then the ? : statements, I did a quick compilation check and it doesn't seem to have any influence. I'll move the __builtin_choose_expr into rt2x00.git for testing and move that patch upstream to wireless-2.6 later. Ivo -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
