I'm writing some code which uses an array initialized with bit shifts by the compiler.
I want the compiler to do the work instead of initializing the array with a for loop.
I am also using the LL suffix here so that it will be 64 bit cross platform.
Is there any problem with using int64_t instead of uint64_t here?
Is there a more idiomatic or correct way to write code like this?
const int64_t map[] = {
['a'] = 1LL<<1, ['b'] = 1LL<<2,
['c'] = 1LL<<3, ['d'] = 1LL<<4,
['e'] = 1LL<<5, ['f'] = 1LL<<6,
['g'] = 1LL<<7, ['h'] = 1LL<<8,
['i'] = 1LL<<9, ['j'] = 1LL<<10,
['k'] = 1LL<<11, ['l'] = 1LL<<12,
['m'] = 1LL<<13, ['n'] = 1LL<<14,
['o'] = 1LL<<15, ['p'] = 1LL<<16,
['q'] = 1LL<<17, ['r'] = 1LL<<18,
['s'] = 1LL<<19, ['t'] = 1LL<<20,
['u'] = 1LL<<21, ['v'] = 1LL<<22,
['w'] = 1LL<<23, ['x'] = 1LL<<24,
['y'] = 1LL<<25, ['z'] = 1LL<<26,
['A'] = 1LL<<27, ['B'] = 1LL<<28,
['C'] = 1LL<<29, ['D'] = 1LL<<30,
['E'] = 1LL<<31, ['F'] = 1LL<<32,
['G'] = 1LL<<33, ['H'] = 1LL<<34,
['I'] = 1LL<<35, ['J'] = 1LL<<36,
['K'] = 1LL<<37, ['L'] = 1LL<<38,
['M'] = 1LL<<39, ['N'] = 1LL<<40,
['O'] = 1LL<<41, ['P'] = 1LL<<42,
['Q'] = 1LL<<43, ['R'] = 1LL<<44,
['S'] = 1LL<<45, ['T'] = 1LL<<46,
['U'] = 1LL<<47, ['V'] = 1LL<<48,
['W'] = 1LL<<49, ['X'] = 1LL<<50,
['Y'] = 1LL<<51, ['Z'] = 1LL<<52,
};
Answer
Is there any problem with using
int64_tinstead ofuint64_there?
No.
All elements of the array are zero or more and <= INT64_MAX and so fit in both int64_t and uint64_t.
Should code have a shift of 63, use uint64_t and 1ULL<<63.