4 ms·

Quick: how would you implement for (i = n; i >= 0; i -= k) with unsigned integers? I just use a signed pointer-size type for all sizes and counters, and stay h

• tzs 10y ago
  If n is not within k of the maximum unsigned integer: i = n+k; do { i -= k; ... } while (i >= k); If n is close enough to the maximum unsigned integer for n+k to overflow: i = n; goto skip_sub; do { i -= k; skip_sub: ... } while (i >= k);
• pbsd 10y ago
  Something like for(size_t i = 0; i <= n; i += k) { work_with(n - i); }? This sort of loop always comes up in these discussions, and I was never convinced that signed integers were worth it for that alone.
  • Sean1708 10y ago
    To be honest I think there are good arguments to both sides, and I don't think there is really a one size fits all solution here. If you use unsigned you've got to pay attention to certain corner cases, if you use signed you've got to pay attention to different corner cases, it's up to you to decide which is more common in your code.
• deleted 10y ago
  [deleted]
• detrino 10y ago
  Your loop: void TestSigned(int min, int max, int step) { for (int i = max; i >= min; i -= step) F(i); } Becomes this with unsigned: void TestUnsigned(unsigned min, unsigned max, unsigned step) { while (true) { F(max); if (max < min + step) break; max -= step; } } Now if I want to transform my loop to operate on pointers or iterators, the transformation is trivial: void TestUnsigned(unsigned *min, unsigned *max, unsigned step) { while (true) { F(*max); if (max < min + step) break; max -= step; } } Quick: Do the same for yours.
  • dsfuoi 10y ago
    It looks easy but it isn't. The second example causes unexpected behavior (and probably ub later) if: min + step > MIN_TYPE_MAX The last example causes undefined behavior if: max - min < step - 1.