even more startup tweaks

c64/kernal/iostack/findfls.s

@@ -0,0 +1,24 @@
+
+// Just a helper routine
+
+// Find the LAT / SAT / FAT entry index where LAT corresponds to A, returns index in Y
+// Carry flag set means not found
+
+find_fls:
+
+	ldy LDTND
+	beq find_fls_not_found // table empty
+!:
+	dey
+	bmi find_fls_not_found // no more entries
+	cmp LAT, y
+	bne !- // does not match, try the next one
+
+	clc
+	rts
+
+find_fls_not_found:
+
+	sec
+	rts
+