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116 lines
2.2 KiB
NASM
116 lines
2.2 KiB
NASM
; *** Requirements ***
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; stdioPutC
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; divide
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;
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; Same as fmtDecimal, but DE is considered a signed number
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fmtDecimalS:
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bit 7, d
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jr z, fmtDecimal ; unset, not negative
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; Invert DE. spit '-', unset bit, then call fmtDecimal
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push de
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ld a, '-'
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ld (hl), a
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inc hl
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ld a, d
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cpl
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ld d, a
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ld a, e
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cpl
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ld e, a
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inc de
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call fmtDecimal
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dec hl
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pop de
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ret
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; Format the number in DE into the string at (HL) in a decimal form.
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; Null-terminated. DE is considered an unsigned number.
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fmtDecimal:
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push ix
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push hl
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push de
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push af
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push hl \ pop ix
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ex de, hl ; orig number now in HL
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ld e, 0
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.loop1:
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call .div10
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push hl ; push remainder. --> lvl E
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inc e
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ld a, b ; result 0?
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or c
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push bc \ pop hl
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jr nz, .loop1 ; not zero, continue
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; We now have C digits to print in the stack.
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; Spit them!
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push ix \ pop hl ; restore orig HL.
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ld b, e
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.loop2:
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pop de ; <-- lvl E
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ld a, '0'
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add a, e
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ld (hl), a
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inc hl
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djnz .loop2
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; null terminate
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xor a
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ld (hl), a
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pop af
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pop de
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pop hl
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pop ix
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ret
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.div10:
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push de
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ld de, 0x000a
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call divide
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pop de
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ret
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; Format the lower nibble of A into a hex char and stores the result in A.
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fmtHex:
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; The idea here is that there's 7 characters between '9' and 'A'
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; in the ASCII table, and so we add 7 if the digit is >9.
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; daa is designed for using Binary Coded Decimal format, where each
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; nibble represents a single base 10 digit. If a nibble has a value >9,
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; it adds 6 to that nibble, carrying to the next nibble and bringing the
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; value back between 0-9. This gives us 6 of that 7 we needed to add, so
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; then we just condtionally set the carry and add that carry, along with
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; a number that maps 0 to '0'. We also need the upper nibble to be a
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; set value, and have the N, C and H flags clear.
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or 0xf0
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daa ; now a =0x50 + the original value + 0x06 if >= 0xfa
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add a, 0xa0 ; cause a carry for the values that were >=0x0a
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adc a, 0x40
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ret
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; Print the hex char in A as a pair of hex digits.
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printHex:
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push af
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; let's start with the leftmost char
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rra \ rra \ rra \ rra
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call fmtHex
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call stdioPutC
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; and now with the rightmost
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pop af \ push af
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call fmtHex
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call stdioPutC
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pop af
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ret
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; Print the hex pair in HL
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printHexPair:
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push af
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ld a, h
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call printHex
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ld a, l
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call printHex
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pop af
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ret
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