Add int to float conversions

src/basic/math/b391.GIVAYF.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - 16-bit signed integer to FAC1
+;
+; Output:
+; - .A - high byte
+; - .Y - low byte
+;
+; Sets the data type flag at $0D to "numeric", stores the number in the FAC1 mantissa
+; then calls convert_i16_to_FAC1
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 107
+; - https://www.c64-wiki.com/wiki/GIVAYF
+;
+
+
+GIVAYF:
+    ldx #$00
+    stx $0D
+    sty FAC1_mantissa
+    sta FAC1_mantissa+1
+    jmp convert_i16_to_FAC1

src/basic/math/b391.interop

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+This is an important floating point math routine, documented in many places.
+
+Example codoe utilizing this routine:
+- https://github.com/irmen/prog8/blob/master/compiler/res/prog8lib/c64flt.p8

src/basic/math/b3a2.convert_Y_to_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - convert uint8 in Y to FAC1
+;
+; Input: Y - uint8 to convert to float
+; Result: FAC1
+;
+; Stores Y into first FAC1 mantissa byte, clears the second and calls convert_i16_to_FAC1
+;
+; - https://www.c64-wiki.com/wiki/BASIC-ROM
+; - https://sta.c64.org/cbm64basconv.html
+; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+convert_Y_to_FAC1:
+    lda #$00
+    sta FAC1_mantissa+1
+    sty FAC1_mantissa
+    jmp convert_i16_to_FAC1

src/basic/math/b3a2.interop

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+This is an important floating point math routine, documented in many places.
+
+Example code utilizing this routine:
+- https://github.com/irmen/prog8/blob/master/compiler/res/prog8lib/c64flt.p8
+

src/basic/math/bc3c.convert_A_to_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - convert int8 in A to FAC1
+;
+; Input: A - int8 to convert to float
+; Result: FAC1
+;
+; Sets first byte of FAC1 to A, sign extends A into tge second byte and falls through to convert_i16_to_FAC1
+;
+; - https://codebase64.org/doku.php?id=base:asm_include_file_for_basic_routines
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+
+convert_A_to_FAC1:
+    sta FAC1_mantissa
+    jsr sign_extend_A_to_Y
+    sty FAC1_mantissa+1
+    +nop                    ; To not leave a gap to the fallthrough
+    ; Fall through to convert_i16_to_FAC1

src/basic/math/bc3c.interop

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+This is an important floating point math routine, documented in many places.
+
+Example code utilizing this routine:
+- https://github.com/irmen/prog8/blob/master/compiler/res/prog8lib/c64flt.p8

src/basic/math/bc44.convert_i16_to_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - Convert signed 16-bit integer to floating point
+;
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+; - https://www.c64-wiki.com/wiki/GIVAYF (which calls this function)
+;
+; Convert the signed 16-bit integer in FAC1 mantissa ($62:$63)
+; into a floating point number in FAC1
+
+; NOTE:
+; According to https://c64os.com/post/floatingpointmath at $BC49
+; Assume FAC1_mantissa+0 and +1. X=exponent and C=0 if negative and C=1 if positive
+
+convert_i16_to_FAC1:
+    ldx #$90
+    jsr carry
+
+    jmp convert_i16_expsign_to_FAC1   ; This should be at $BC49 (see note above)
+
+
+carry:
+    lda FAC1_mantissa+1
+    cmp #$80                    ; Copy sign into carry
+    rts

src/basic/math/bc44.interop

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

src/basic/math/convert_i16_expsign_to_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - convert i16 with exponent in X and sign in C to FAC1
+
+convert_i16_expsign_to_FAC1:
+
+    lda #$00                    
+    sta FAC1_mantissa+2         ; Clear high bytes of mantissa
+    sta FAC1_mantissa+3
+    stx FAC1_exponent
+    sta FAC1_sign
+    bcs @1
+
+    ; Handle signed int
+    lda FAC1_mantissa+1          ; Clear sign bit of int 16
+    and #$7F
+    sta FAC1_mantissa+1
+    ldy #>CONST_NEG_32768       ; Subtract with 32768 to invert negative number
+    lda #<CONST_NEG_32768
+    jsr add_MEM_FAC1
+@1: jmp normal_FAC1

src/basic/math/sign_extend_A_to_Y.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - helper function to sign extend accumulator into Y
+
+sign_extend_A_to_Y:
+    cmp #$80                ; Copy sign into carry
+    ldy #$00                ; Y = $00
+    bcc @1                  ; Branch if not negative
+    dey                     ; Y = $FF
+@1: rts