the bits of 4-bit number in i. func reverseBits(i int) int { i = ((i << 2) & 0xc) | ((i >> 2) & 0x3) i = ((i << 1) & 0xa) | ((i >> 1) & 0x5) return i } // ghashAdd adds two elements of GF(2¹²⁸) and returns the sum. func ghashAdd(x, y *gcmFieldElement) gcmFieldElement { // Addition in a characteristic 2 field is just XOR. return gcmFieldElement{x.low ^ y.low, x.high ^ y.high} } // ghashDouble returns the result of doubling an element of GF(2¹²⁸). func ghashDouble(x *gcmFieldElement) (double gcmFieldElement)...