From: Mark Wooding <mdw@distorted.org.uk>
Date: Sun, 14 Nov 2021 10:28:22 +0000 (+0000)
Subject: Import yesterday's source.
X-Git-Url: https://git.distorted.org.uk/~mdw/zx-fizzbuzz/commitdiff_plain/a221d644f4371212a32875ed05fa6dfafb31e51e

Import yesterday's source.
---

a221d644f4371212a32875ed05fa6dfafb31e51e
diff --git a/fizzbuzz.s b/fizzbuzz.s
new file mode 100644
index 0000000..58d4928
--- /dev/null
+++ b/fizzbuzz.s
@@ -0,0 +1,166 @@
+;;; -*-asm-*-
+;;;
+;;; Best not to ask why.
+
+	org	0xf000
+
+print_a: equ	0x10
+tvflag:	equ	0x5c3c
+
+entry:
+	;; Initialize the buffer.
+	ld	a, 1
+	ld	(buf), a
+	ld	(len), a
+
+	;; Use the main screen.
+	xor	a
+	ld	(tvflag), a
+
+	;; Look at the buffer and decide what to do.
+again:	ld	e, 0
+
+	;; First, decide whether it's a multiple of three.  This is a bit
+	;; fiddly.
+	ld	a, (len)
+	ld	b, a
+	ld	hl, buf
+	xor	a
+
+	;; Main `mod 3' loop.  Load a byte and add it into the accumulator in
+	;; decimal.
+mod3:	ld	c, (hl)
+	inc	hl
+	add	a, c
+	daa
+	jr	nc, mod3_1
+	call	squish
+	add	a, 1
+	daa
+mod3_1:	djnz	mod3
+
+	call	squish
+	call	squish
+
+	cp	0
+	jr	z, prfizz
+	cp	3
+	jr	z, prfizz
+	cp	6
+	jr	z, prfizz
+	cp	9
+	jr	nz, nofizz
+
+prfizz:	ld	hl, fizz
+	call	print
+	inc	e
+
+	;; Next, decide whether it's a multiple of five.  This is easier.
+nofizz:	ld	a, (buf)
+	and	0x0f
+	jr	z, prbuzz
+	cp	5
+	jr	nz, nobuzz
+
+prbuzz:	ld	hl, buzz
+	call	print
+	jr	prnl
+
+	;; Not a multiple of five.  Skip ahead if it was a multiple of three.
+nobuzz:	ld	a, e
+	cp	0
+	jr	nz, prnl
+
+	;; OK, so just print the value.
+	ld	a, (len)
+	ld	b, 0
+	ld	c, a
+	ld	hl, buf - 1
+	add	hl, bc
+	ld	b, c
+
+	ld	a, (hl)
+	ld	d, a
+	srl	a
+	srl	a
+	srl	a
+	srl	a
+	jr	z, skiplz
+	or	0x30
+	rst	print_a
+skiplz:	ld	a, d
+	and	0x0f
+	or	0x30
+	rst	print_a
+	dec	b
+	jr	z, prnl
+
+prdig:	dec	hl
+	ld	a, (hl)
+	ld	d, a
+	srl	a
+	srl	a
+	srl	a
+	srl	a
+	or	0x30
+	rst	print_a
+	ld	a, d
+	and	0x0f
+	or	0x30
+	rst	print_a
+	djnz	prdig
+
+	;; Print the newline.
+prnl:	ld	a, ' '
+	rst	print_a
+
+	;; Increment the counter.
+	ld	hl, buf
+	ld	a, (len)
+	ld	b, a
+	scf
+incr:	ld	a, (hl)
+	adc	a, 0
+	daa
+	ld	(hl), a
+	jp	nc, again
+	inc	hl
+	djnz	incr
+
+	;; Carry out.
+	ld	a, (len)
+	ld	b, 0
+	ld	c, a
+	ld	hl, buf
+	add	hl, bc
+	ld	(hl), 1
+	inc	a
+	ld	(len), a
+	jp	again
+
+squish:
+	;; Add the two halves of a.
+	ld	c, a
+	and	0x0f
+	srl	c
+	srl	c
+	srl	c
+	srl	c
+	add	a, c
+	daa
+	ret
+
+print:
+	;; Print the string at hl.
+	ld	a, (hl)
+	cp	0
+	ret	z
+	rst	print_a
+	inc	hl
+	jr	print
+
+fizz:	defb	"fizz", 0
+buzz:	defb	"buzz", 0
+
+len:	defb	0
+buf:	defs	256