finding color of bits

hi
i am reading thru a book on digitizing text lines using c code.They
use a font data file containing unsigned char fonts [][16] with
elements like 0x00,0x7e,0x81 etc to represent each character .After a
text line is scanned 16 times the equivalent codes are stored in an
unsigned char[] bitImage.
Now the digitized line stored in bitImage is taken 1 character at a
time(ie 8 bits) and color of each is to be determined whether black or
white.
The book says that 'quickest method will be to write assembler code to
shift each octect(ie bitImage[i] in a for loop of i=0 to
i<bitImageSize) left 8 times so that carry flag will have color of
each bit'.The book says that no high level language can access the
carry flag and so a different method needs to be found.

I didn't quite understand that part.can someone clarify..?

The book continues to point out that 'bits in each octect can be got
by shifting it and ANDing with a constant'.Being new to bit
manipulation etc i couldn't quite write the code.if someone can help
pls do.

Finally the book comes up with a solution ,defining an unsigned char
c =0x80 and uses it as below

....
#define WHITE 0x00
#define BLACK 0xff
....
unsigned char octet ;
unsigned char *bit_image ;
....
currentcolor =WHITE

for (i=0 ; i<bitImageSize ; i++){
octet=bit_image[i] ;
...
for (c=0x80 ; c ; c>>=1){
if ((currentcolor&c)==(octet&c)) incrmntcurrentRunlength();
else startNewRunlength();
}
....
}

if somebody can explain what happens in this loop it would be a great
help..Being a beginner in c/bit manip etc i find it a little difficult
to understand these..

thanks in adv
harry
.

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