implemented NORMAL math routine, added more stubs

c64/basic/math/NORMAL.s

@@ -0,0 +1,100 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - normalize FAC1
+//
+// See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 113
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+// - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+//
+
+// XXX test this
+
+NORMAL:
+
+	lda FAC1_exponent
+	beq normal_end                     // branch if our float is 0
+	
+	lda FAC1_mantissa+3
+	beq normal_by_byte                 // branch if we can move the whole byte
+	
+	and #$80
+	bne normal_end                     // branch if already normalized
+	
+	// FALLTROUGH
+	
+normal_by_bit:
+	
+	// First check the current exponent
+	
+	lda FAC1_exponent
+	cmp #$01
+	bne !+
+	
+	// Exponent is 1 - just mark the whole number as 0 and finish
+	
+	lda #$00
+	sta FAC1_exponent
+	rts
+!:
+	// Multiply the mantissa by 2
+
+	clc
+	rol FACOV
+	rol FAC1_mantissa+0
+	rol FAC1_mantissa+1
+	rol FAC1_mantissa+2
+	rol FAC1_mantissa+3
+	
+	bcc NORMAL                         // branch if next iteration needed
+	rts
+	
+normal_by_byte:
+
+	// First decrement the exponent by 8, but not below 0
+	
+	lda FAC1_exponent
+	sec
+	sbc #$08
+	bcs !+
+	lda #$00
+!:
+	sta FAC1_exponent
+	beq normal_end                     // branch if our float reached 0
+
+	// Now multiply the mantissa by 8 by moving the whole bytes
+	
+	lda FAC1_mantissa+2
+	sta FAC1_mantissa+3
+	lda FAC1_mantissa+1
+	sta FAC1_mantissa+2
+	lda FAC1_mantissa+0
+	sta FAC1_mantissa+1
+	
+	lda FACOV
+	sta FAC1_mantissa+0
+
+	lda #$00
+	sta FACOV
+	
+	// Now check if mantissa is not 0
+	
+	ora FAC1_mantissa+0
+	ora FAC1_mantissa+1
+	ora FAC1_mantissa+2
+	ora FAC1_mantissa+3
+	
+	bne NORMAL                         // not 0 - branch to next iteration
+
+	// Our mantissa reached 0 - mark exponent as 0 and finish
+	
+	sta FAC1_exponent
+
+	// FALLTROUGH
+
+normal_end:
+
+	rts

c64/basic/math/b8fe.NORMAL.jmp.s

@@ -0,0 +1,7 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// Just a compatibility jump - our routine is longer than original one
+
+	jmp NORMAL

c64/basic/math/b8fe.interop

@@ -0,0 +1,3 @@
+This is an important floating point math routine, documented in many places.
+
+XXX - try to find real-life example