begin implementing routine to print packed messages

c64/basic/print_packed_message.s

@@ -0,0 +1,157 @@
+	;; This routine prints messages that have been packed
+	;; using the make_error_tables program.
+	;; The general idea is to save space in the ROM.
+
+	;; The output of make_error_tables is written to packed_messages.s, and
+	;; contains the following:
+	;; 
+	;; packed_message_words - List of nybl packed words.
+	;; packed_message_tokens - List of tokens that get joined to make messages
+	;; packed_message_chars - List of characters in messages sorted by frequency.
+	
+print_packed_message:
+	;; X = message number
+
+	lda #$ff
+	ldy #$ff
+packed_message_search:	
+	iny
+	cpx #$00
+	beq found_message_in_token_stream
+	lda packed_message_tokens,y
+	cmp #$ff
+	bne +
+	dex
+*
+	cpy #$ff
+	bne packed_message_search
+	;; Could not find message
+	sec
+	rts
+
+found_message_in_token_stream:
+	;; Now print each word in the message
+	tya
+	pha
+	lda packed_message_tokens,y
+	cmp #$ff
+	beq +
+	jsr print_packed_word
+	lda #$20
+	jsr $ffd2
+	pla
+	tay
+	iny
+	bne found_message_in_token_stream
+*
+	rts
+
+print_packed_word:
+	;; A = the word to print
+	tax
+
+	;; Find the word in the list
+	ldy #$ff
+packed_word_search:	
+	cpx #$00
+	beq found_packed_word
+	iny
+	lda packed_message_words,y
+	and #$0f
+	cmp #$00
+	bne +
+	dex
+*
+	cpy #$ff
+	bne packed_word_search
+	;; Could not find word
+	sec
+	rts
+
+found_packed_word:
+	inc $0427
+	
+	;; Y = offset into packed word data - 1
+	iny
+
+	;; Check for end of word
+	lda packed_message_words,y
+	cmp #$00
+	beq done_printing_word
+	and #$f0
+	beq done_printing_word
+
+	;; Check if it is an uncommon char
+	lda packed_message_words,y
+	and #$f0
+	cmp #$f0
+	beq is_uncommon_char
+
+	;; Is not an uncommon char, so get char of upper nybl
+	lda packed_message_words,y
+
+	;; Put high nybl into low bits of X
+	lsr
+	lsr
+	lsr
+	lsr
+	tax
+
+	;; Save Y so it doesn't get clobbered by $FFD2
+	tya
+	pha
+
+	;; X=1-14 = first 14 chars, so subtract one
+	lda packed_message_chars-1,x
+	jsr $FFD2
+	inc $426
+
+	;; See if there is a char in the low nybl to print
+	pla
+	tay
+	lda packed_message_words,y
+	and #$0f
+	beq no_lo_nybl_char
+	cmp #$0f
+	beq no_lo_nybl_char
+
+has_lo_nybl_char:	
+	;; We need to print the low nybl char as well
+	tax
+	tya
+	pha
+
+	;; Skip lower nybls of $F or $0 in nybl packed
+	;; bytes, as these do not encode characters
+	cpx #$f
+	beq +
+	cpx #0
+	beq +
+	
+	;; X=1-14 = first 14 chars, so subtract one
+	lda packed_message_chars-1,x
+	jsr $FFD2
+	inc $426	
+*
+	pla
+	tay
+	cpy #$ff
+	;; FALL THROUGH
+
+no_lo_nybl_char:
+
+	bne found_packed_word
+	;; Hit end of packed data
+	rts
+
+is_uncommon_char:
+	;; Lower nybl has offset into low-frequency part of the table
+
+	lda packed_message_words,y
+	and #$0f
+	clc
+	adc #14
+	jmp has_lo_nybl_char
+	
+done_printing_word:
+	rts