Robert P. J. Day schrieb: > On Thu, 23 Apr 2009, Julia Lawall wrote: > >> On Thu, 23 Apr 2009, Robert P. J. Day wrote: >> >>> On Thu, 23 Apr 2009, Julia Lawall wrote: >>> >>>> I found 8 occurrences with the following Coccinelle semantic match: >>>> >>>> @@ expression n; @@ >>>> >>>> * (n & (n-1)) == 0 >>>> >>>> >>>> The most unpleasant was: >>>> >>>> (!(((fp)->ipend & ~0x30) & (((fp)->ipend & ~0x30) - 1))) >>>> >>>> in the file arch/blackfin/kernel/traps.c. >>>> >>>> At least some of them seemed to have comments nearby that suggested >>>> that searching for a single 1-bit was indeed the goal. I haven't >>>> looked at all of them, though. >>> behold, the power of shell and REs, which searches for four >>> variations of that test: >> Actually, it seems that it was specifying == 0 that was not really >> necessary. Perhaps the possibility of parentheses is useful too. >> >> With the following semantic patch, I find 93 occurrences. >> >> @@ expression n; @@ >> >> * (n) & ((n)-1) >> >> That could indeed be worth doing something about, if they are indeed all >> representing a check for a single bit. > > they're not. we're actually now discussing this on the main LKML, > but that construct -- n & (n - 1) -- has two semantic meanings: > > a) power of two? > b) single bit set? > > mathematically, those two things have the same form but > *semantically* they're read very differently, which is why i'm > proposing to add a simple function or two for single-bit testing that > would make a lot of the code easier to read. > > rday > -- > hi all, glibc provides in sys/param.h a set a macros (seem to come from BSD): #define NBBY CHAR_BIT ... #define setbit(a,i) ((a)[(i)/NBBY] |= 1<<((i)%NBBY)) #define clrbit(a,i) ((a)[(i)/NBBY] &= ~(1<<((i)%NBBY))) #define isset(a,i) ((a)[(i)/NBBY] & (1<<((i)%NBBY))) #define isclr(a,i) (((a)[(i)/NBBY] & (1<<((i)%NBBY))) == 0) IMHO this is readable. This could be a nice starting point (or endpoint ?) for a S&R mission. re, wh -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
