constant_time_msb_s
*outlen = constant_time_select_s(constant_time_msb_s(ret), *outlen, ret);
return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
return constant_time_msb_s(~a & (a - 1));
*outlen = constant_time_select_s(constant_time_msb_s(ret), *outlen, ret);