float problems on c64

docs/source/todo.rst

@@ -1,7 +1,7 @@
 TODO
 ====
 - fix on c64 target: examples/cube3d-float (broken since 9.3 with the evalstack removal)  it works on x16 target, oddly enough.
-  More detailed and simpler code for this problem in floatproblem64.p8
+  More detailed and simpler code for this problem in floatproblem64.p8 / floatproblem64.asm (the minified version)
 
 - fix: search for TODO("swap operand order")
 - optimize: search for TODO optimize: don't use scratch var

floatproblem64.asm

@@ -0,0 +1,144 @@
+
+.cpu  '6502'
+
+CHROUT = $FFD2
+
+; C64 addresses for float routines:
+;MOVFM = $bba2
+;CONUPK = $ba8c
+;MOVAF = $bc0c
+;MOVMF = $bbd4
+;FOUT = $bddd
+;FADDT = $b86a
+;FMULTT = $ba2b
+; CX16 addresses for float routines:
+MOVFM = $fe63
+CONUPK = $fe5a
+MOVAF = $fe6c
+MOVMF = $fe66
+FOUT = $fe06
+FADDT = $fe1b
+FMULTT = $fe21
+
+* = $0801
+
+; 10 SYS 2062
+	.word  (+), 10
+	.null  $9e, " 2062"
++	.word  0
+
+; program starts here at address 2062
+	lda  #$8d
+	jsr  CHROUT
+
+	; calculate: value1*one + value2*one
+	; (yes the multiplications with one do nothing value-wise, but they influence the routines being called...)
+	lda  #<prog8_float_const_0	; -0.8
+	ldy  #>prog8_float_const_0
+	jsr  MOVFM			; FAC1 = -0.8
+	lda  #<float_const_one		; 1.0
+	ldy  #>float_const_one
+	jsr  CONUPK			; ARG = 1.0
+	jsr  FMULTT			; FAC1 = -0.8*1.0 = -0.8
+	jsr  pushFAC1			; save value...
+	lda  #<prog8_float_const_1	; 0.3
+	ldy  #>prog8_float_const_1
+	jsr  MOVFM			; FAC1 = 0.3
+	lda  #<float_const_one		; 1.0
+	ldy  #>float_const_one
+	jsr  CONUPK			; ARG = 1.0
+	jsr  FMULTT			; FAC1 = 0.3*1.0 = 0.3
+	jsr  MOVAF			; ARG = FAC1 = 0.3
+	jsr  popFAC1			; restore value... (-0.8)
+	jsr  FADDT			; FAC1 = -0.8 + 0.3 = -0.5
+	; ... result in FAC1 will be wrong on C64 (1.1 instead of -0.5)....
+
+	; print FAC1
+	jsr  FOUT		; fac1 to string in A/Y
+	sta  _mod+1
+	sty  _mod+2
+	ldy  #0
+_mod	lda  $ffff,y		; modified
+	beq  +
+	jsr  CHROUT
+	iny
+	bne  _mod
++	lda  #$8d
+	jsr  CHROUT
+
+	; print expected
+	ldy #0
+-	lda  string_1,y
+	beq  +
+	jsr  CHROUT
+	iny
+	bne  -
++	rts
+
+string_1
+	.text "-.5 was expected",$8d,0
+
+
+floats_temp_var         .byte  0,0,0,0,0        ; temporary storage for a float
+
+pushFAC1
+	;-- push floating point in FAC onto the cpu stack
+	; save return address
+	pla
+	sta  returnaddr
+	pla
+	sta  returnaddr+1
+	ldx  #<floats_temp_var
+	ldy  #>floats_temp_var
+	jsr  MOVMF
+	lda  floats_temp_var
+	pha
+	lda  floats_temp_var+1
+	pha
+	lda  floats_temp_var+2
+	pha
+	lda  floats_temp_var+3
+	pha
+	lda  floats_temp_var+4
+	pha
+	; re-push return address
+	lda  returnaddr+1
+	pha
+	lda  returnaddr
+	pha
+	rts
+
+returnaddr  .word 0
+
+popFAC1
+	; -- pop floating point value from cpu stack into FAC1
+	; save return address
+	pla
+	sta  returnaddr
+	pla
+	sta  returnaddr+1
+	pla
+	sta  floats_temp_var+4
+	pla
+	sta  floats_temp_var+3
+	pla
+	sta  floats_temp_var+2
+	pla
+	sta  floats_temp_var+1
+	pla
+	sta  floats_temp_var
+	lda  #<floats_temp_var
+	ldy  #>floats_temp_var
+	jsr  MOVFM
+	; re-push return address
+	lda  returnaddr+1
+	pha
+	lda  returnaddr
+	pha
+	rts
+
+
+; global float constants
+prog8_float_const_0	.byte  $80, $cc, $cc, $cc, $cc  ; float -0.8
+prog8_float_const_1	.byte  $7f, $19, $99, $99, $99  ; float 0.3
+float_const_one	.byte  $81, $00, $00, $00, $00  ; float 1.0

floatproblem64.p8

@@ -1,32 +1,57 @@
 %import textio
 %import floats
+%import test_stack
 %zeropage dontuse
 
 main {
     sub start()  {
         float value1 = -0.8
         float value2 = 0.3
-        float two = 2.0
+        float one = 1.0
 
-        float result = value1*two + value2*two  ; TODO FIX: invalid result on c64, ok when the *two is removed or expression is split (it's not caused by pushFAC1/popFAC1)
+        float result = value1*one + value2*one  ; TODO FIX: invalid result on c64, ok when the *one is removed or expression is split (it's not caused by pushFAC1/popFAC1)
+        ; TODO is it floats.CONUPK??
         floats.print_f(result)
         txt.nl()
-        txt.print("-1 was expected\n\n")       ; on C64: -1.1 is printed :(
+        txt.print("-.5 was expected\n\n")       ; on C64: -1.1 is printed :(
 
-        result = value2*two + value1*two        ; swapped operands around, now it's suddenly fine on C64...
+;        result = value2*one + value1*one        ; swapped operands around, now it's suddenly fine on C64...
-        floats.print_f(result)
+;        floats.print_f(result)
-        txt.nl()
+;        txt.nl()
-        txt.print("-1 was expected\n\n")       ; on C64: correct value is printed
+;        txt.print("-.5 was expected\n\n")       ; on C64: correct value is printed
 
 
-        value1 = 0.8
+;        value1 = 0.8
-        value2 = 0.3
+;        value2 = 0.3
-        result = value1*two + value2*two
+;        result = value1*one + value2*one
-        floats.print_f(result)
+;        floats.print_f(result)
-        txt.nl()
+;        txt.nl()
-        txt.print("2.2 was expected\n\n")       ; on C64: correct value is printed
+;        txt.print("1.1 was expected\n\n")       ; on C64: correct value is printed
+;
+;        printFAC1()
+;        printFAC1()
+;        printFAC1()
 
         repeat {
         }
     }
+
+    sub printFAC1() {
+        ubyte[20] fac_save
+        sys.memcopy($60, fac_save, sizeof(fac_save))
+        txt.print("fac1=")
+        %asm {{
+		jsr  floats.FOUT		; fac1 to string in A/Y
+		sta  P8ZP_SCRATCH_W1
+		sty  P8ZP_SCRATCH_W1+1
+		ldy  #0
+-		lda  (P8ZP_SCRATCH_W1),y
+		beq  +
+		jsr  cbm.CHROUT
+		iny
+		bne  -
++       }}
+        txt.nl()
+        sys.memcopy(fac_save, $60, sizeof(fac_save))
+    }
 }