feat(catalan): Implement modulo

1 files changed, 29 insertions, 0 deletions

diff --git a/catalan/math.a65 b/catalan/math.a65
index 434fd8d..7bd850a 100644
--- a/catalan/math.a65
+++ b/catalan/math.a65
@@ -66,5 +66,34 @@ arg		.byt 0
 subtrahend	.byt 0
 .)
 
+; a %= moda_arg
+moda .(
+	ldx arg		; x = arg
+	cpx #1		; if (x <= 1)
+	bcc r_zero	;   return 0
+	beq r_zero
+
+	ora #0		; Update flags, so they're accurate with the accumulator value
+	beq return	; if (a == 0) return a
+
+	cmp arg		; if (a < arg)
+	bcc return	;   return a
+	ldx #0		; x = 0
+
+loop	sec		; do  carry = 1
+	sbc arg		;     a -= arg + !carry
+	inx		;     ++x
+	cmp arg		; while (a >= arg)
+	bcs loop
+
+return	rts
+
+r_zero	lda #0
+	rts
+
++moda_arg
+arg		.byt 0
+.)
+
 #endif /* CATALAN_MATH */
 // vim: noet ts=9 sw=0 lcs=tab\:\ \