Add tan_FAC1

src/basic/math/e2b4.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/e2b4.tan_FAC1.s

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+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - tangent of FAC1 in radians
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 210
+; - 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/TAN
+
+; tan(x) = sin(x) / cos(x)
+
+tan_FAC1:
+    jsr mov_r_FAC1_TMP1         ; TMP1 = x
+    jsr sin_FAC1                ; FAC1 = sin(x)
+    jsr mov_r_FAC1_TMP2         ; TMP2 = sin(x)
+    lda #TEMPF1
+    ldy #0
+    jsr mov_MEM_FAC1            ; FAC1 = x
+    jsr COS                     ; FAC1 = cos(x)
+    lda #TEMPF2
+    ldy #0
+    jsr mov_MEM_FAC2            ; FAC2 = sin(x)
+    jmp div_FAC2_FAC1           ; FAC1 = tan(x)