more sane directory name, updated binaries

src/basic/math_mov/mov_MEM_FAC1.s

@@ -0,0 +1,79 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// Math package - fetch FAC1 from RAM location
+//
+// Input:
+// - .A - address low byte
+// - .Y - address high byte
+//
+// Output:
+// - .A - FAC1 exponent, affects status flags
+// - .Y - always 0
+//
+// Preserves:
+// - .X - (experimentation with original ROM)
+//
+// See also:
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+// - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+
+// XXX test this
+
+mov_MEM_FAC1:
+
+	// Original routines use $22/$23 location for a vector too, see here:
+	// - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+
+	sty INDEX+1
+	sta INDEX+0
+
+	// Now copy the data from RAM to FAC2, for the format description see:
+	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic#Representation_in_the_C-64
+
+	// Copy the mantissa
+
+	ldy #$04
+	lda (INDEX), y
+	sta FAC1_mantissa+3
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+2
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+1
+
+	dey
+	lda (INDEX), y
+	ora #$80                           // clear the sign bit
+	sta FAC1_mantissa+0
+
+	// Copy the sign
+
+	lda (INDEX), y
+	bpl !+                             // assumption: non-negative numbers are more frequent
+	lda #$FF
+	skip_2_bytes_trash_nvz
+!:
+	lda #$00
+
+	sta FAC1_sign
+
+	// Copy the exponent
+
+	dey
+	lda (INDEX), y
+	sta FAC1_exponent
+
+	// Set low order mantissa to 0 - this should give the
+	// most precision while operating on integers
+
+	sty FACOV
+
+	// Return the FAC1 exponent
+
+	lda FAC1_exponent
+	rts