feat(catalan): Implement multiplication with the accumulator subroutine

1 files changed, 44 insertions, 2 deletions

diff --git a/catalan/catalan.a65 b/catalan/catalan.a65
index 7dc73b0..3dd3168 100644
--- a/catalan/catalan.a65
+++ b/catalan/catalan.a65
@@ -3,6 +3,7 @@
 
 hello	.byt "HELLO, WORLD!",0
 
+// accumulator = a * b
 #define multiply(a, b) .(                     :\
 	lda a       ; if (a == 0)             :\
 	beq return  ;   return 0              :\
@@ -21,6 +22,7 @@ loop	clc         ; do  carry = 0           :\
 return                                        :\
 .)
 
+// accumulator = a / b
 #define divide(a, b) .(                        :\
 	lda b       ; if (b == 0)              :\
 	beq return  ;   return 0               :\
@@ -38,11 +40,51 @@ loop	sec         ; do  carry = 1            :\
 return  txa                                    :\
 .)
 
-main	print(hello)
-	divide(#253, #5)
+cat_n	.byt 1
+n	.byt 0
+
+main
+	lda #3
+	sta multa_arg1
+	lda #14
+	jsr multa
 	putchar()
 	rts
 
+// a *= multa_arg1
+multa .(
+	beq return	; if (a == 0) return a
+	cmp #1		; if (a == 1)
+	beq r_arg1	;   return arg1
+
+	ldx arg1	; x = arg1
+	cpx #0		; if (x == 0)
+	beq r_zero	;   return 0
+	cpx #1		; if (x == 1)
+	beq return	;   return a
+
+	dex		; --x  // accumulator already has the first value
+	sta addend	; addend = a
+loop	clc		; do  carry = 0
+	adc addend	;     a += addend + carry
+	dex		;     --x
+	cpx #1		; while (x >= 1)
+	bcs loop
+
+return	ora #0		; Update flags, so they're accurate with the accumulator value
+	rts
+
+r_zero	lda #0
+	rts
+
+r_arg1	lda arg1
+	rts
+
++multa_arg1
+arg1		.byt 0
+addend		.byt 0
+.)
+
 buffer	.byt 0
 
 // vim: noet ts=8 sw=0 lcs=tab\:\ \