work on parsing numbers from strings.

c64/basic/inject_number.s

@@ -0,0 +1,111 @@
+	;; Parse a number from the input buffer at $0200+tokenise_work1
+	;; Result is put into FAC1.
+	;; tokenise_work1 is updated with first position after the number.
+
+	;; XXX - Remember decimal position and exponent, and apply them
+	;; after to produce normalised floating point number.
+
+ij_not_a_digit:
+	;; XXX check for ".", "E", "+" and "-"
+	;; Other chars terminate the accumulation.
+	CLC
+	RTS
+	
+inject_number:
+	;; Clear FAC1
+	jsr erase_fac1
+
+	;; Clear decimal position flag
+	lda #$ff
+	sta tokenise_work2
+
+	;; Check if leading char is a - sign
+	;; Note: the - will have been tokenised to $AB
+	;; XXX - implement
+	
+ij_loop1:	
+	ldx tokenise_work1
+	lda $0200,x
+	cmp #$30
+	bcc ij_not_a_digit
+	cmp #$39
+	bcs ij_not_a_digit
+
+	;; It is a digit
+
+	;; Only add digit if we have not overflowed the accuracy of
+	;; the mantissa
+	lda basic_fac1_exponent
+	beq ij_accept_precision
+
+	;; We have an extra digit after saturating our precision.
+	;; Thus we should ignore the digit, and just multiply the FAC
+	;; by 10, but only if we have not seen a decimal point.
+	;; If we have seen a decimal point, then we can completely ignore
+	;; the digit, as it is contributing not recordable information
+
+	lda tokenise_work2
+	cmp #$ff
+	bne ij_seen_decimal_point
+	
+	jsr fac1_mul10
+	;; Fall through
+ij_seen_decimal_point:
+	jmp ij_consider_next_digit
+	
+ij_accept_precision:
+	;; We can accept more precision, so multiply the mantissa by 10, so that
+	;; we can add the new digit in
+	jsr fac1_mul10
+
+	lda basic_fac1_exponent
+	bne ij_consider_next_digit
+	
+	;; Get digit
+	ldx tokenise_work1
+	lda $0200,x
+	sec
+	sbc #$30
+
+	;; Add to FAC1 mantissa
+	clc
+	adc basic_fac1_mantissa+0
+	sta basic_fac1_mantissa+0
+	ldx #1
+	ldy #3
+ij_loop2:	
+	lda basic_fac1_mantissa,x
+	adc #$00
+	sta basic_fac1_mantissa+1,x
+	inx
+	dey
+	bne ij_loop2
+
+	bcc +
+	;; Carry set, so we have overflowed.
+	;; We should shift everything right one digit, and increase
+	;; the exponent by one.  The non-zero exponent tells us that we
+	;; can't fit any more precision in.
+	jsr fac1_mantissa_div2
+*
+
+ij_consider_next_digit:	
+	;; Consider next digit
+	inc tokenise_work1
+	jmp ij_loop1
+	
+	rts
+
+
+erase_fac1:	
+	lda #$00
+	ldx #7
+*
+	sta basic_fac1_exponent,x
+	dex
+	bpl -
+	sta basic_fac1_mantissa_lob
+
+	rts
+	
+