more work on variables support

src/basic/engine/fetch_variable.s

@@ -77,8 +77,135 @@ fetch_variable_type_string:
 
 fetch_variable_find_addr:
 
-	// Now try to find variable address
+	// Now try to find variable address between VARTAB and ARYTAB, see
+	// - https://www.c64-wiki.com/wiki/Memory_(BASIC)
+
+	lda VARTAB+0
+	sta VARPNT+0
+	lda VARTAB+1
+	sta VARPNT+1
+
+	// FALLTROUGH
+
+fetch_variable_find_addr_loop:
+
+	// Check if end of search loop
+
+	lda VARPNT+1
+	cmp ARYTAB+1
+	bne !+
+	lda VARPNT+0
+	cmp VARPNT+0
+	beq fetch_variable_alocate
+!:
+	// Compare current variable name with searched one
+	// XXX consider creating optimized version for 46K/50K memory models
+
+	ldy #$00
+
+#if CONFIG_MEMORY_MODEL_60K
+	ldx #<VARPNT
+	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_VARPNT
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (VARPNT),y
+#endif
+
+	cmp VARNAM+0
+	bne fetch_variable_find_addr_next
+
+	iny
+
+#if CONFIG_MEMORY_MODEL_60K
+	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_VARPNT
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (VARPNT),y
+#endif
+
+	cmp VARNAM+1
+	bne fetch_variable_find_addr_next
+
+	// FALLTROUGH
+
+fetch_variable_adjust_VARPNT:
+
+	// Adjust VARPNT to point just after variable name and quit
+
+#if !HAS_OPCODES_65CE02
+
+	clc
+	lda VARPNT+0
+	adc #$02
+	sta VARPNT+0
+	bcc !+
+	inc VARPNT+1
+!:
+#else // HAS_OPCODES_65CE02
+
+	inw VARPNT
+	inw VARPNT
+
+#endif
+
+	rts
+
+fetch_variable_find_addr_next:
+
+	// Increase VARPNT by 7 - constant value, each variable uses 7 bytes, see:
+	// - https://sites.google.com/site/h2obsession/CBM/basic/variable-format
+
+	clc
+	lda VARPNT+0
+	adc #$07
+	sta VARPNT+0
+	bcc fetch_variable_find_addr_loop
+	inc VARPNT+1
+	bne fetch_variable_find_addr_loop  // branch always
+
+fetch_variable_alocate:
+	
+	// First check if we have enough space for a new descriptor
 
 	// XXX
 
-	rts
+	// If needed, move all the arrays up
+
+	// XXX
+
+	// Set pointer to new variable
+
+	// XXX
+
+	// Fill-in the new variable name, descriptor (it is enough to zero first 2 bytes of content)
+
+	ldy #$00
+
+#if CONFIG_MEMORY_MODEL_60K
+	
+	// XXX
+
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	
+	lda VARNAM+0
+	sta (VARPNT),y
+	iny
+	lda VARNAM+1
+	sta (VARPNT),y
+	iny
+	lda #$00
+	sta (VARPNT),y
+	iny
+	sta (VARPNT),y
+
+#endif
+
+	// Adjust variable pointer and quit
+
+#if HAS_OPCODES_65C02
+	bra fetch_variable_adjust_VARPNT
+#else
+	jmp fetch_variable_adjust_VARPNT
+#endif