Question about function atoi_b16 in loader.c

[cchappyboy]

I have a question about function atoi_16(char *s ) that is in file c:\program\picc\drivers\loader.c

Please give an answer. Thanks.
I am just confused. I can not make sense of function atoi_b16(char *s).

It said this function for convert two hex characters to a int8.

if *s is a hex, I think just let it move left 4 times and let & the other one. then we can get int8.

if *s is a byte, i think we can do the same way as about then get int8.

But the program shows like this

[PCM programmer]

The hex values are ASCII characters. For example, the string "3A"
has two ASCII bytes in it, 0x33 and 0x41.

The purpose of the function is to convert the ASCII bytes to a binary
integer. The comment above the function should be:

[Guest]

Thank you so much!!!