signExtend

[Sign extend] variable bit-width integer.

signExtend(x, [w])
// x: variable bit-width integer
// w: bit width (32)

const xbit = require('extra-bit');

xbit.signExtend(15, 4);
// → -1 (1111 ⇒ -1)

xbit.signExtend(3, 3);
// → 3  (011 ⇒ 3)

xbit.signExtend(4, 3);
// → -4 (100 ⇒ -4)

References

• Bit Twiddling Hacks: By Sean Eron Anderson