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base:ascii_char_to_4_bit_integer

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base:ascii_char_to_4_bit_integer [2015-04-17 04:30] (current)
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 +====== 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...
 + 
 +<code 6502acme>
 +  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
 +</code>
base/ascii_char_to_4_bit_integer.txt ยท Last modified: 2015-04-17 04:30 (external edit)