What is the fastest way to bytewise examine the contetnt of quadword
Yes, it can be done.  Here is one reasonable approach.  First XOR the value with 0x0A0A..0A:

t = x ^ 0x0A0A0A0A0A0A0A0A0A0A0A0A0A0A0A0A;


So now the problem becomes testing whether y contains a zero byte.  First we'll replace every byte with a single bit that is 1 if the byte is non-zero, or 0 if the byte is zero:

u = t | (t&gt;&gt;4);
u = u | (u&gt;&gt;2);
u = u | (u&gt;&gt;1);


(Here we only care about the least significant bit of each byte; the remaining bit positions hold garbage that we don't care about.)  Now we'll flip each of those bits:

v = ~u;


At this point the LSB of each byte is 1 if the original value contained a 0x0A there, or 0 otherwise.  So, we'll test whether any of these bits are 1:

w = v | (v&gt;&gt;64);
w = w | (w&gt;&gt;32);
w = w | (w&gt;&gt;16);
w = w | (w&gt;&gt;8);
y = w &amp; 1;


At this point, y is the result you are looking for: it will be 1 if the original value had a 0x0A byte anywhere, or 0 otherwise.