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63 lines
1.6 KiB
NASM
63 lines
1.6 KiB
NASM
INCLUDE "constants.asm"
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; if DEBUG
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SECTION "home/print_bcd.asm", ROM0
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; else
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; SECTION "BCD Functions", ROM0[$3A76]
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; endc
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; function to print a BCD (Binary-coded decimal) number
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; de = address of BCD number
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; hl = destination address
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; c = flags and length
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; bit 7: if set, do not print leading zeroes
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; if unset, print leading zeroes
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; bit 6: if set, left-align the string (do not pad empty digits with spaces)
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; if unset, right-align the string
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; bits 0-5: length of BCD number in bytes
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; Note that bits 5 and 7 are modified during execution. The above reflects
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; their meaning at the beginning of the functions's execution.
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PrintBCDNumber:: ; 3ab2 (0:3ab2)
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ld b, c ; save flags in b
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res 7, c
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res 6, c ; c now holds the length
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.loop
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ld a, [de]
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swap a
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call PrintBCDDigit
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ld a, [de]
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call PrintBCDDigit
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inc de
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dec c
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jr nz, .loop
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bit 7, b ; were any non-zero digits printed?
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jr z, .done
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.numberEqualsZero ; if every digit of the BCD number is zero
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bit 6, b
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jr nz, .skipRightAlignmentAdjustment
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dec hl ; if the string is right-aligned, it needs
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.skipRightAlignmentAdjustment ;to be moved back one space
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ld [hl], "０"
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call PrintLetterDelay
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inc hl
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.done
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ret
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PrintBCDDigit:: ; 3ad5 (0:3ad5)
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and $0f
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and a
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jr z, .zeroDigit
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res 7, b ; unset 7 to indicate that a nonzero
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.outputDigit ; digit has been reached
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add "０"
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ld [hli], a
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jp PrintLetterDelay
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.zeroDigit
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bit 7, b ; either printing leading zeroes or
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jr z, .outputDigit ; already reached a nonzero digit?
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bit 6, b
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ret nz ; left-align, don't pad with space
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ld a, " "
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ld [hli], a
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ret
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; 0x3aed |