Add sin_FAC1

src/basic/math/e26b.interop

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+This is an important floating point math routine, documented in many places.
+
+Usage example:
+- https://www.lemon64.com/forum/viewtopic.php?t=10492

src/basic/math/e26b.sin_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - sine of FAC1 in radians
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 210 - XXX address does not match
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+; - https://www.c64-wiki.com/wiki/SIN
+
+
+
+sin_FAC1:
+
+    jsr mov_FAC1_FAC2               ; FAC1 <- X / (2*pi)     (X2)
+    ldy #>const_DOUBLE_PI
+    lda #<const_DOUBLE_PI
+    jsr mov_MEM_FAC1
+    jsr div_FAC2_FAC1
+
+    jsr mov_FAC1_FAC2               ; FAC2 <- X2
+    jsr int_FAC1                    ; FAC1 <- INT(X2)
+    jsr sub_FAC2_FAC1               ; FAC1 <- X2 - INT(X2)   (F)
+
+    ldy #>const_QUARTER
+    lda #<const_QUARTER
+    jsr FCOMP
+    bmi sin_next                    ; FAC1 < 0.25
+
+    ldy #>sin_three_quarters
+    lda #<sin_three_quarters
+    jsr FCOMP
+    bmi sin_q23                     ; FAC1 < 0.75
+
+    jsr mov_FAC1_FAC2               ; FAC1 <- FAC1 - 1.0
+    ldy #>const_ONE
+    lda #<const_ONE
+    jsr mov_MEM_FAC1
+    jsr sub_FAC2_FAC1
+    +bra sin_next
+
+sin_q23:
+    ldy #>const_HALF
+    lda #<const_HALF
+    jsr sub_MEM_FAC1                ; FAC1 <- 0.5 - FAC1
+
+    ; FALLTHROUGH
+    
+sin_next:
+    ldy #>poly_sin
+    lda #<poly_sin
+    jmp poly1_FAC1

src/basic/math/poly_sin.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *  BASIC_0  #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+; Polynomial for the sine function
+
+
+poly_sin:
+
+	!byte $05                          ; series length - 1
+
+	+PUT_CONST_POLY_SIN_1
+	+PUT_CONST_POLY_SIN_2
+	+PUT_CONST_POLY_SIN_3
+	+PUT_CONST_POLY_SIN_4
+	+PUT_CONST_POLY_SIN_5
+	+PUT_CONST_POLY_SIN_6
+
+	
+; Constant 0.75 needed for sine calculation
+sin_three_quarters:
+    !byte $80, $40, $00, $00, $00