P2 coding trick
Cluso99
Posts: 18,069
I noticed this very smart coding trick Chip used in checking for a hex character (0..9, A..F, a..f).
I also found a shorter way to convert it to a binary nibble.
Then we strip of the upper nibble from both the "0..9" and "J..O"/"j..o" leaving $00..$0F"
While it's shorter code to first check for ASCII $80 and above, rather than using the 8 long table we could use a 4 long table. This would save 2 longs.
But I believe Chip is looking for the quickest code.
I also found a shorter way to convert it to a binary nibble.
hexchrs long %00000000_00000000_00000000_00000000 long %00000011_11111111_00000000_00000000 '"0".."9" long %00000000_00000000_00000000_01111110 '"A".."F" long %00000000_00000000_00000000_01111110 '"a".."f" long %00000000_00000000_00000000_00000000 long %00000000_00000000_00000000_00000000 long %00000000_00000000_00000000_00000000 long %00000000_00000000_00000000_00000000 .check altb x,#hexchrs 'check for hex testb 0,x wc if_nc ret 'if not hex, c=0 testbn x,#6 wz 'hex, "0".."9"? if_z sub x,#"0" 'if so, make $0..$9 if_nz bitl x,#5 'else, force uppercase if_nz sub x,#"A"-10 '..make $A..$F ret 'c=1Shorter conversion
.check altb x,#hexchrs 'check for hex
testb 0,x wc
if_nc ret 'if not hex, c=0
testbn x,#6 wz 'hex, "0".."9"?
if_nz add x,#9 '..make low nibble $A..$F
_ret_ and x,#$F 'extract low nibble, return c=1
The add x,#9 converts "A..F" to "J..O" and "a..f" to "j..o". "J" is ascii $4A and "j" is ascii $6A.Then we strip of the upper nibble from both the "0..9" and "J..O"/"j..o" leaving $00..$0F"
While it's shorter code to first check for ASCII $80 and above, rather than using the 8 long table we could use a 4 long table. This would save 2 longs.
But I believe Chip is looking for the quickest code.
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