Hi, All:
I am reading the following code:
unsigned long crcbitbybitfast(unsigned char* p, unsigned long len) {
// fast bit by bit algorithm without augmented zero bytes.
// does not use lookup table, suited for polynom orders between
132.
unsigned long i, j, c, bit;
unsigned long crc = crcinit_direct;
for (i=0; i<len; i++) {
c = (unsigned long)*p++;
for (j=0x80; j; j1) {
bit = crc & crchighbit;
crc<<= 1;
if (c & j) bit^= crchighbit;
if (bit) crc^= polynom;
}
}
if (refout) crc=reflect(crc, order);
crc^= crcxor;
crc&= crcmask;
return(crc);
}
bit^= crchighbit; what is that mean?
Thanks for any clue.
bin YE

"yezi" <ye_line@hotmail.comwrote in message
news:1133198789.981261.185160@
Hi, All:

I am reading the following code:

unsigned long crcbitbybitfast(unsigned char* p, unsigned long len) {

// fast bit by bit algorithm without augmented zero bytes.
// does not use lookup table, suited for polynom orders between
132.

unsigned long i, j, c, bit;
unsigned long crc = crcinit_direct;

for (i=0; i<len; i++) {

c = (unsigned long)*p++;

for (j=0x80; j; j1) {

bit = crc & crchighbit;
crc<<= 1;
if (c & j) bit^= crchighbit;
if (bit) crc^= polynom;
}
}

if (refout) crc=reflect(crc, order);
crc^= crcxor;
crc&= crcmask;

return(crc);
}

bit^= crchighbit; what is that mean?

it means:

bit = bit ^ crchighbit

^ means bitwise X

"pemo" <usenetmeisterr@gmail.comwrote in message
news:dmfeqi$smk$1@news.ox.ac.uk

"yezi" <ye_line@hotmail.comwrote in message
news:1133198789.981261.185160@
>Hi, All:
>>
>I am reading the following code:
>>
>unsigned long crcbitbybitfast(unsigned char* p, unsigned long len) {
>>
>// fast bit by bit algorithm without augmented zero bytes.
>// does not use lookup table, suited for polynom orders between
>132.
>>
>unsigned long i, j, c, bit;
>unsigned long crc = crcinit_direct;
>>
>for (i=0; i<len; i++) {
>>
>c = (unsigned long)*p++;
>>
>for (j=0x80; j; j1) {
>>
>bit = crc & crchighbit;
>crc<<= 1;
>if (c & j) bit^= crchighbit;
>if (bit) crc^= polynom;
>}
>}
>>
>if (refout) crc=reflect(crc, order);
>crc^= crcxor;
>crc&= crcmask;
>>
>return(crc);
>}
>>
>
>
>bit^= crchighbit; what is that mean?
>
it means:

bit = bit ^ crchighbit

^ means bitwise X

course, you can turn it into a logical(ish) operator via: !! e.g.,

bit = !!bit ^ !!crchighbit