I used the following C code earlier this year (use at your own peril): https://github.com/nsajko/numericcompfricas/blob/master/check/checker.c#L234 https://gith

I used the following C code earlier this year (use at your own peril): https://github.com/nsajko/numericcompfricas/blob/master/check/checker.c#L234 https://github.com/nsajko/numericcompfricas/blob/master/chec... Distance between 0.0 and -0.0 is taken to be 0. If x or y are NaN, the distance is taken to be the greatest positive value of the return type. Replace mfloat_t with double. Replace int64 with long or similar. int64 ud(mfloat_t x, mfloat_t y) { // Handle NaNs. if (x != x || y != y) { return (int64)(~0UL >> 1); } union {mfloat_t X; uint64 a;} u1; union {mfloat_t Y; uint64 b;} u2; u1.X = x; u2.Y = y; uint64 a = u1.a, b = u2.b; if ((a & (1UL << 63)) == (b & (1UL << 63))) { // a and b are of the same sign. a = a - b; if ((a & (1UL << 63))) { return -a; } return a; } return (int64)(a - (1UL << 63) + b); } Using memcpy could be more portable than using unions, but I think it doesn't really matter. EDIT: The Musl libc, for example, also uses unions instead of memcpy: https://git.musl-libc.org/cgit/musl/tree/src/math/nextafterf.c https://git.musl-libc.org/cgit/musl/tree/src/math/nextafterf...