more sane directory name, updated binaries

src/basic/math/bfb4.toggle_sign_FAC1.s

@@ -0,0 +1,27 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - toggle FAC1 sign (if not 0)
+//
+// See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 117
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+//
+
+toggle_sign_FAC1:
+
+	lda FAC1_exponent
+	beq !+                             // do not toggle the sign if value is 0
+
+	// FALLTROUGH
+
+toggle_sign_FAC1_skipcheck:            // entry for other routines
+
+	lda FAC1_sign
+	eor #$FF
+	sta FAC1_sign
+!:
+	rts