How to code a modulo (%) operator in C/C++/Obj-C that handles negative numbers

user_435129 0
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One of my pet hates of C-derived languages (as a mathematician) is that

(-1) % 8 // comes out as -1, and not 7

fmodf(-1,8) // fails similarly

What's the best solution?

C++ allows the possibility of templates and operator overloading, but both of these are murky waters for me. examples gratefully received.

c++11 modulo operator-overloading c c++
16 Answers

For a solution that uses no branches and only 1 mod, you can do the following

// Works for other sizes too,
// assuming you change 63 to the appropriate value
int64_t mod(int64_t x, int64_t div) {
  return (x % div) + (((x >> 63) ^ (div >> 63)) & div);
}
user_2579780
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