213 lines
4.2 KiB
ArmAsm
213 lines
4.2 KiB
ArmAsm
// #LAYOUT# STD * #TAKE
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// #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
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// #LAYOUT# * BASIC_0 #TAKE
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// #LAYOUT# * * #IGNORE
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// Well-known BASIC routine, described in:
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//
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// - [CM64] Computes Mapping the Commodore 64 - page 102
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// - https://sta.c64.org/cbm64basconv.html
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//
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// Output:
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// - VALTYP - $00 = floating number, $FF = string
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// - INTFLG (XXX float/integer, probably)
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// - for float: FAC1
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// - for string: __FAC1 + 0 = length, __FAC1 + 1 = pointer to string
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//
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// Idea:
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// - use a stack to reorder operations, so that they can be executed
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// in a correct order
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//
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// XXX finish the implementation
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FRMEVL:
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// Put the sentinel to the stack
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lda #$00
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pha
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// FALLTROUGH
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FRMEVL_loop:
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// Check if end of statement
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jsr end_of_statement_check
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bcs_16 do_SYNTAX_error
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// There are 4 basic possibilities: a string, a float, an opening bracket, or a token
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jsr fetch_character
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cmp #$22 // check for opening quote
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beq FRMEVL_fetch_string
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cmp #$28 // check for opening bracket
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beq FRMEVL_handle_bracket
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cmp #$7F // check for a token
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bcc FRMEVL_fetch_float
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// Search for a value or unary operator, starting from the most probable
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// XXX check for BASIC functions here, too
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cmp #$AB // check for unary minus
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beq_16 do_NOT_IMPLEMENTED_error // XXX
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cmp #$A8 // check for NOT
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beq_16 do_NOT_IMPLEMENTED_error // XXX
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cmp #$FF // check for PI
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beq_16 do_NOT_IMPLEMENTED_error // XXX
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cmp #$AA // check for unary plus (ignore this one)
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beq FRMEVL_loop
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// Nothing recognized
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jmp do_SYNTAX_error
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FRMEVL_handle_bracket:
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// Brackets are easy to handle - just call FRMEVL recursively
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// and consume the closing bracket afterwards
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jsr FRMEVL
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jsr fetch_character
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cmp #$29 // closing bracket
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beq FRMEVL_got_value
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jmp do_SYNTAX_error
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FRMEVL_fetch_float:
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// XXX implement this
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jmp do_SYNTAX_error
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FRMEVL_fetch_string:
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// Mark return value as a string, set initial length as 0
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ldx #$FF
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stx VALTYP
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inx
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stx __FAC1 + 0
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// Set pointer to start of the string
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ldx TXTPTR + 0
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stx __FAC1 + 1
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ldx TXTPTR + 1
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stx __FAC1 + 2
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!:
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// Search for closing quote
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jsr fetch_character
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cmp #$22
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beq FRMEVL_got_value
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inc __FAC1 + 0
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bne !-
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jmp do_STRING_TOO_LONG_error
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FRMEVL_got_value:
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jsr end_of_statement_check
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bcs FRMEVL_calculate
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// FALLTROUGH
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FRMEVL_fetch_operator:
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// We have a value, but this is not the end of expression. We expect
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// a two argument operator here. First make sure we have enough space
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// on a stack - we will surely need it
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tsx
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cpx #$40 // XXX is this a safe threshold?
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bcc_16 do_FORMULA_TOO_COMPLEX_error
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// Now look for an operator
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// XXX for now only plus operator is implemented
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jsr fetch_character
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cmp #$AA // check for a plus operator
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beq FRMEVL_push_value_operator
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// Something unknown - consider this the end of expression
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jsr unconsume_character
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// FALTROUGH
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FRMEVL_calculate: // this is the exit point for the operators
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// Now, we have to calculate all the operations; at this point we
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// should have a value in FAC1 and (possibly) operator on the top of the stack
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pla
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beq FRMEVL_done // branch if sentinel
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// Priority does not matter at this point - just jump to the operator
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// FALLTROUGH
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FRMEVL_done:
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rts
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FRMEVL_push_value_operator:
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// First push the return address
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lda #>(FRMEVL_calculate - 1)
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pha
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lda #<(FRMEVL_calculate - 1)
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pha
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// Push the value from FAC1
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ldx VALTYP
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bmi FRMEVL_push_string
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// Push float
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// XXX implement this
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FRMEVL_push_string:
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// Push string - address, length, type
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lda __FAC1+1
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pha
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lda __FAC1+2
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pha
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lda __FAC1+0
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pha
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txa
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pha
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FRMEVL_push_operator_address:
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// Push the operator address to stack, in a form
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// suitable for RTS
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// XXX add support for other operators
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lda #>(oper_plus - 1)
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pha
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lda #<(oper_plus - 1)
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pha
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// Push operator priority
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lda #$01 // XXX add support for other operators
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pha
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// Continue
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jmp FRMEVL_loop
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