implemented few trivial math routines

Makefile

@@ -14,6 +14,7 @@ SRCDIR_BASIC   = $(SRCDIR_COMMON) \
                  c64/basic/,stubs_math \
                  c64/basic/commands \
                  c64/basic/init \
+                 c64/basic/math \
                  c64/basic/rom_revision
 
 SRCDIR_KERNAL  = $(SRCDIR_COMMON) \

STATUS.md

@@ -179,17 +179,17 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B1AA`   | `FACINX`     | NOT DONE | convert FAC1 to 16-bit signed integer              |
 | `$B391`   | `GIVAYF`     | NOT DONE | XXX - no stub added yet                            |
 | `$B7B5`   | `STRVAL`     | NOT DONE | XXX - no stub added yet                            |
-| `$B850`   | `FSUB`       | NOT DONE | subtract FAC1 from RAM                             |
+| `$B850`   | `FSUB`       | PARTIAL  | needs `CONUPK` and `FSUBT`                         |
 | `$B853`   | `FSUBT`      | NOT DONE | subtract FAC1 from FAC2                            |
-| `$B867`   | `FADD`       | NOT DONE | add RAM to FAC1                                    |
+| `$B867`   | `FADD`       | PARTIAL  | needs `CONUPK` and `FADDT`                         |
 | `$B86A`   | `FADDT`      | NOT DONE | add FAC2 to FAC1                                   |
 | `$B9EA`   | `LOG`        | NOT DONE | XXX - no stub added yet                            |
-| `$BA28`   | `FMUL`       | NOT DONE | multiplies FAC1 by RAM                             |
+| `$BA28`   | `FMUL`       | PARTIAL  | needs `CONUPK` and `FMULT`                         |
 | `$BA2B`   | `FMULT`      | NOT DONE | multiplies FAC1 by FAC2                            |
 | `$BA8C`   | `CONUPK`     | NOT DONE | fetch FAC2 from RAM location                       |
 | `$BAE2`   | `MUL10`      | NOT DONE | multiply FAC1 by 10                                |
 | `$BAFE`   | `DIV10`      | NOT DONE | divide FAC1 by 10, result is always positive       |
-| `$BB0F`   | `FDIV`       | NOT DONE | divide RAM by FAC1                                 |
+| `$BB0F`   | `FDIV`       | PARTIAL  | needs `CONUPK` and `FDIVT`                         |
 | `$BB12`   | `FDIVT`      | NOT DONE | divide FAC2 by FAC1, ignores sign                  |
 | `$BBA2`   | `MOVFM`      | NOT DONE | fetch FAC1 from RAM location                       |
 | `$BBD4`   | `MOVMF`      | NOT DONE | copy FAC1 to memory location, rounds if asked      |

c64/basic/math/b850.FSUB.s

@@ -15,7 +15,8 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX provide implementation
-
 FSUB:
-	STUB_IMPLEMENTATION()
+
+	jsr CONUPK
+
+	// FALLTROUGH to FSUBT

c64/basic/math/b867.FADD.s

@@ -15,7 +15,8 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX provide implementation
-
 FADD:
-	STUB_IMPLEMENTATION()
+
+	jsr CONUPK
+
+	// FALLTROUGH to FADDT

c64/basic/math/ba28.FMUL.s

@@ -18,7 +18,8 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX provide implementation
-
 FMUL:
-	STUB_IMPLEMENTATION()
+
+	jsr CONUPK
+
+	// FALLTROUGH to FMULT

c64/basic/math/bb0f.FDIV.s

@@ -15,7 +15,8 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX provide implementation
-
 FDIV:
-	STUB_IMPLEMENTATION()
+
+	jsr CONUPK
+
+	// FALLTROUGH to FDIVT