CONSTANT_TIME_CARRY
h1 += (c = CONSTANT_TIME_CARRY(h0, c));
h2 += CONSTANT_TIME_CARRY(h1, c);
h1 += (c = CONSTANT_TIME_CARRY(h0, c));
h2 += (c = CONSTANT_TIME_CARRY(h1, c));
h3 += (c = CONSTANT_TIME_CARRY(h2, c));
h4 += CONSTANT_TIME_CARRY(h3, c);