The most useful user-made C-macros (in GCC, also C99)? [closed]

Answer 1

#define kroundup32(x) (--(x), (x)|=(x)>>1, (x)|=(x)>>2, (x)|=(x)>>4, (x)|=(x)>>8, (x)|=(x)>>16, ++(x))

Find the closest 32bit unsigned integer that is larger than x. I use this to double the size of arrays (i.e. the high-water mark).