Bit twiddling to get sign bit of 32 bit int

Question

I would like to convert

(n < 0 ? 1 : 0)

into bit twiddling (assuming 2s complement arch).

for performance reasons.

Answer 1

With an unsigned shift,

x = n >>> 31; // Java's unsigned shift

x = (int)((uint)n >> 31); // C#'s unsigned shift, the casts are effectively nop

GCC does this automatically, other compilers may also. Or not. Your mileage may vary.