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Moved and indented comment about fmtHex's method

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Clanmaster21 2019-10-21 02:23:49 +01:00 committed by GitHub
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1 changed files with 9 additions and 10 deletions
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kernel/core.asm
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@ -183,17 +183,16 @@ findchar:
; Format the lower nibble of A into a hex char and stores the result in A.
; The idea here is that in the ASCII table, there's 7 characters between
; '9' and 'A', and so we add 7 if the digit is >9.
; daa is designed for using Binary Coded Decimal format, where each
; nibble represents a single base 10 digit. If a nibble has a value
; greater than 9, it adds 6 to that nibble, carrying a 1 to the next
; nibble and bringing the value back between 0-9. This gives us 6 of that
; 7 we needed to add, so then we just condtionally set the carry and
; add that carry, along with a number that maps 0 to '0'.
fmtHex:
; we need to make the upper nibble a known value
; also clears the N, C and H flags for daa
; The idea here is that there's 7 characters between '9' and 'A'
; in the ASCII table, and so we add 7 if the digit is >9.
; daa is designed for using Binary Coded Decimal format, where each
; nibble represents a single base 10 digit. If a nibble has a value >9,
; it adds 6 to that nibble, carrying to the next nibble and bringing the
; value back between 0-9. This gives us 6 of that 7 we needed to add, so
; then we just condtionally set the carry and add that carry, along with
; a number that maps 0 to '0'. We also need the upper nibble to be a
; set value, and have the N, C and H flags clear.
or 0xf0
daa ; now a =0x50 + the original value + 0x06 if >= 0xfa
add a, 0xa0 ; cause a carry for the values that were >=0x0a