document limited fp support

docs/source/index.rst

@@ -68,7 +68,7 @@ Language features
 - ``in`` expression for concise and efficient multi-value/containment test
 - Nested subroutines can access variables from outer scopes to avoids the overhead to pass everything via parameters
 - Variable data types include signed and unsigned bytes and words, arrays, strings.
-- Floating point math also supported if the target system provides floating point library routines (C64 and Cx16 both do).
+- Floating point math also supported on select compiler targets (C64, Cx16 and virtual).
 - Strings can contain escaped characters but also many symbols directly if they have a PETSCII equivalent, such as "♠♥♣♦π▚●○╳". Characters like ^, _, \\, {, } and | are also accepted and converted to the closest PETSCII equivalents.
 - High-level code optimizations, such as const-folding (zero-allocation constants that are optimized away in expressions), expression and statement simplifications/rewriting.
 - Many built-in functions, such as ``sin``, ``cos``, ``abs``, ``sqrt``, ``msb``, ``rol``, ``ror``, ``sort`` and ``reverse``

docs/source/libraries.rst

@@ -220,6 +220,10 @@ Provides string manipulation routines.
 
 floats
 ------
+
+.. note::
+    Floating point support is only available on c64, cx16 and virtual targets for now.
+
 Provides definitions for the ROM/Kernal subroutines and utility routines dealing with floating
 point variables.  This includes ``print_f``, the routine used to print floating point numbers,
 ``fabs`` to get the absolute value of a floating point number, and a dozen or so floating point

docs/source/programming.rst

@@ -255,11 +255,13 @@ This saves a lot of memory and may be faster as well.
 Floating point numbers
 ^^^^^^^^^^^^^^^^^^^^^^
 
-Floats are stored in the 5-byte 'MFLPT' format that is used on CBM machines,
-and currently all floating point operations are specific to the Commodore 64.
-This is because routines in the C64 BASIC and Kernal ROMs are used for that.
-So floating point operations will only work if the C64 BASIC ROM (and Kernal ROM)
-are banked in.
+Floats are stored in the 5-byte 'MFLPT' format that is used on CBM machines.
+Floating point support is available on the c64 and cx16 (and virtual) compiler targets.
+On the c64 and cx16, the rom routines are used for floating point operations,
+so on both systems the correct rom banks have to be banked in to make this work.
+Although the C128 shares the same floating point format, Prog8 currently doesn't support
+using floating point on that system (because the c128 fp routines require the fp variables
+to be in another ram bank than the program, something Prog8 doesn't do).
 
 Also your code needs to import the ``floats`` library to enable floating point support
 in the compiler, and to gain access to the floating point routines.
@@ -268,10 +270,6 @@ to worry about this yourself)
 
 The largest 5-byte MFLPT float that can be stored is: **1.7014118345e+38**   (negative: **-1.7014118345e+38**)
 
-.. note::
-    On the Commander X16, to use floating point operations, ROM bank 4 has to be enabled (BASIC).
-    Importing the ``floats`` library will do this for you if needed.
-
 
 Arrays
 ^^^^^^

docs/source/todo.rst

@@ -42,7 +42,6 @@ For 9.0 major changes
 
 Need help with
 ^^^^^^^^^^^^^^
-- c128 target: various machine specific things (free zp locations, how banking works, getting the floating point routines working, ...)
 - atari target: more details details about the machine, fixing library routines. I have no clue whatsoever.
 - see the :ref:`portingguide` for details on what information is needed.
 
@@ -68,11 +67,10 @@ Compiler:
   But all library code written in asm uses .proc already..... (textual search/replace when writing the actual asm?)
   Once new codegen is written that is based on the IR, this point is mostly moot anyway as that will have its own dead code removal on the IR level.
 - Zig-like try-based error handling where the V flag could indicate error condition? and/or BRK to jump into monitor on failure? (has to set BRK vector for that) But the V flag is also set on certain normal instructions
-
+- For c128 target; put floating point variables in bank 1 to make the FP routines work (is this even worth it? very few people will use fp)
 
 Libraries:
 
-- fix the problems in c128 target, and flesh out its libraries.
 - fix the problems in atari target, and flesh out its libraries.
 - c64: make the graphics.BITMAP_ADDRESS configurable (VIC banking)
 - optimize several inner loops in gfx2 even further?