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213 lines
7.0 KiB
Markdown
213 lines
7.0 KiB
Markdown
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## cc65 floating point support
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WARNING: the following is just a brain dump after a long weekend of hacking. it
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sure needs cleanup etc :)
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The current goal is to implement ieee754 support in the compiler, using the
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"float" datatype as the common 32bit float. ANYTHING ELSE COMES LATER
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You can not use any of this to write software yet. Dont bother. This is for
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people who want to help pushing the floating point support further.
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- build the compiler/toolchain/libs from this fptest branch
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- now you can build the programs in this directory
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right now you'll have to use the cbm kernal wrapper library, as that is pretty
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much the only one that somewhat works :)
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feel free to work on "real" ieee754 functions (see below)
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## The Compiler
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- for the time being i will handle and test only expressions where left and
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right side are both floats. that will enable me to fix and test a fair portion
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of what has to be done, before i will have to dive into the ugly areas of type
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conversion and casting.
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NOT WORKING YET:
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- float values as in "12.34f" work, but "12.34" does not - should it?
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- compare, float const vs float const
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- substraction, float variable - float constant (compile error)
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- multiplication operator, float const * float const (compile error)
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- division operator, float const / float const
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- ternary operator (compile error)
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- addition, float constant + float variable (compiles but does not work)
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(and probably more :))
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TODO (much later):
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- add a cmdline option to the compiler to switch the float binary type (754, cbm,
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woz, ...). -> remember the code in fp.c/h
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### Files & Functions
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#### codegen.c
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```
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g_getimmed Load a constant into the primary register
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g_getstatic Fetch an static memory cell into the primary register
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g_getlocal Fetch specified local object (local var) into the primary register
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g_putstatic
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g_reglong
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g_regfloat Make sure, the value in the primary register a float. Convert if necessary
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g_typeadjust
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g_typecast Cast the value in the primary register to the operand size that is flagged by the lhs value
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oper Encode a binary operation.
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g_push
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g_push_float Push the primary register or a constant value onto the stack
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g_inc
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g_dec
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g_defdata
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g_defdata_float
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(see below) g_add, g_sub, g_mul, g_div, g_neg, g_bneg
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(see below) g_eq, g_ne, g_lt, g_gt, g_le, g_ge
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(invalid) g_mod, g_or, g_xor, g_and, g_asr
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```
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#### datatype.c
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```
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ArithmeticConvert
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```
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#### expr.c
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```
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LimitExprValue
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parseadd
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parsesub
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```
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#### initdata.c
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```
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DefineData Output a data definition for the given expression
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```
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#### loadexpr.c
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```
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LoadExpr
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```
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#### locals.c
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```
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ParseAutoDecl
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```
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#### assignment.c
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```
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OpAssignArithmetic Parse an "=" (if 'Gen' is 0) or "op=" operation for arithmetic lhs
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```
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#### fp.c
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wrapper for doing floating point operations on target floats
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```
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FP_D_As32bitRaw converts double into 32bit (float) and then returns its raw content as a 32bit int
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```
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--------------------------------------------------------------------------------
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## The Library
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cbmkernal:
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this is a wrapper to the CBM kernal functions
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- this one is fairly complete and should be OK to use when fixing/adding basic
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things in the compiler
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- the only missing functions are ftosrsubeax, fnegeax - which can be easily
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added once testcode is found that actually triggers it :)
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ieee754:
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this should become a freestanding ieee754 library
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- basically everything missing except addition/substraction
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- compare functions are missing
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- mul, div functions are missing
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- type conversion functions are missing
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woz:
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historical float routines by woz :) unfortunately not ieee754
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- (optionally) converting from/to ieee754 format is missing (compile time option)
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- compare functions are missing
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- type conversion functions are missing
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--------------------------------------------------------------------------------
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### runtime functions
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these must be available in the runtime library
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```
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func description cbmfp wozfp 754 codegen.c
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aufloat Primary 8bit unsigned -> float * - - g_regfloat
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afloat Primary 8bit signed -> float * - - g_regfloat
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axufloat Primary 16bit unsigned -> float * - - g_regfloat
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axfloat Primary 16bit signed -> float * - - g_regfloat
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eaxufloat Primary 32bit unsigned -> float * - - g_regfloat
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eaxfloat Primary 32bit signed -> float * - - g_regfloat
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feaxint Primary float -> 16bit int * - - g_regint
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feaxlong Primary float -> 32bit long * - - g_reglong
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ftosaddeax Primary = TOS + Primary * ? ? g_add
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ftossubeax Primary = TOS - Primary * ? ? g_sub
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ftosrsubeax Primary = Primary - TOS - - - g_rsub
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ftosmuleax Primary = TOS * Primary * ? - g_mul
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ftosdiveax Primary = TOS / Primary * ? - g_div
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fnegeax Primary = -Primary - - - g_neg
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fbnegeax Primary = !Primary (return bool!) * - - g_bneg
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ftosgeeax Test for greater than or equal to * - - g_ge
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ftosgteax Test for greater than * - - g_gt
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ftosleeax Test for less than or equal to * - - g_le
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ftoslteax Test for less than * - - g_lt
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ftosneeax Test for not equal * - - g_ne
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ftoseqeax Test for equal * - - g_eq
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```
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### extra functions
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optional utility functions.
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```
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func description cbmfp wozfp 754
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char *_ftostr(char *d, float s) * ? ? for printf family
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float _strtof(char *d) * - - for scanf family
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```
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### math.h functions
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these are optional, required for standard libm
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```
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func description cbmfp wozfp 754
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/* C99 */
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float powf(float f, float a) * - -
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float sinf(float s) * - -
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float cosf(float s) * - -
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float logf(float x) * * -
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float expf(float x) * - -
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float sqrtf(float x) * - -
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float tanf(float x) * - -
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float atanf(float x) * - -
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float fabsf(float x) * - -
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float roundf(float x) * - -
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float truncf(float x) * - -
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```
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--------------------------------------------------------------------------------
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- https://www.geeksforgeeks.org/ieee-standard-754-floating-point-numbers/
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- https://www.h-schmidt.net/FloatConverter/IEEE754.html
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