base:ascii_char_to_4_bit_integer
ASCII Char to 4 bit integer
This is a very simple routine that converts an ASCII char contained in 'a' to a 4 bit number returned in 'a'. It can deal with upper/lowercase hex letters 'a'..'f' as well as 'A'..'F' and returns the error code 255 for nonvalid input like 'g'..'z', 'G'…'Z' or other non hex digits like interpunction, spaces, math symbols etc…
sec sbc #'0' bcc error cmp #10 bcc return nondigit and #$3f cmp #('f'-'0'+1) bcs error cmp #('a'-'0') bcc error sbc #('a'-'0'-10) rts error lda #255 return rts
base/ascii_char_to_4_bit_integer.txt · Last modified: 2015-04-17 04:30 by 127.0.0.1