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. Harvey -- 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
