fs: check for file size bounds in GetC

apps/zasm/glue.asm

@@ -36,6 +36,7 @@
 ; fsGetC
 ; fsSeek
 ; fsTell
+; cpHLDE
 ; FS_HANDLE_SIZE
 
 ; *** Variables ***

apps/zasm/util.asm

@@ -12,16 +12,6 @@ callHL:
 	jp	(hl)
 	ret
 
-; Compare HL with DE and sets Z and C in the same way as a regular cp X where
-; HL is A and DE is X.
-cpHLDE:
-	ld	a, h
-	cp	d
-	ret	nz	; if not equal, flags are correct
-	ld	a, l
-	cp	e
-	ret		; flags are correct
-
 ; HL - DE -> HL
 subDEFromHL:
 	push	af

kernel/core.asm

@@ -22,6 +22,7 @@ addDE:
 .end:
 	ld	e, a
 	pop	af
+noop:				; piggy backing on the first "ret" we have
 	ret
 
 ; copy (DE) into DE, little endian style (addresses in z80 are always have
@@ -71,6 +72,16 @@ subHL:
 	pop	af
 	ret
 
+; Compare HL with DE and sets Z and C in the same way as a regular cp X where
+; HL is A and DE is X.
+cpHLDE:
+	ld	a, h
+	cp	d
+	ret	nz	; if not equal, flags are correct
+	ld	a, l
+	cp	e
+	ret		; flags are correct
+
 ; Write the contents of HL in (DE)
 writeHLinDE:
 	push	af
@@ -84,14 +95,12 @@ writeHLinDE:
 	ret
 
 ; jump to the location pointed to by IX. This allows us to call IX instead of
-; just jumping it. We use IX because we never use this for arguments.
+; just jumping it. We use IX because we seldom use this for arguments.
 callIX:
 	jp	(ix)
-	ret
 
 callIY:
 	jp	(iy)
-	ret
 
 ; Ensures that Z is unset (more complicated than it sounds...)
 unsetZ:

kernel/fs.asm

@@ -87,7 +87,8 @@
 ; Size in bytes of a FS handle:
 ; * 4 bytes for starting offset of the FS block
 ; * 2 bytes for current position relative to block's position
-.equ	FS_HANDLE_SIZE		6
+; * 2 bytes for file size
+.equ	FS_HANDLE_SIZE		8
 .equ	FS_ERR_NO_FS		0x5
 .equ	FS_ERR_NOT_FOUND	0x6
 
@@ -387,6 +388,11 @@ fsOpen:
 	; Current pos
 	ld	hl, FS_METASIZE
 	call	writeHLinDE
+	inc	de
+	inc	de
+	; file size
+	ld      hl, (FS_META+FS_META_FSIZE_OFFSET)
+	call	writeHLinDE
 	pop	af
 	pop	de
 	pop	hl
@@ -429,11 +435,37 @@ fsAdvanceH:
 	pop	af
 	ret
 
+; Sets Z according to whether file handle at (DE) is within bounds, that is, if
+; current position is smaller than file size.
+fsHandleWithinBounds:
+	push	hl
+	; current pos in HL, adjusted to remove FS_METASIZE
+	call	fsTell
+	push	de
+	push	de \ pop ix
+	; file size
+	ld	e, (ix+6)
+	ld	d, (ix+7)
+	call	cpHLDE
+	pop	de
+	pop	hl
+	jr	nc, .outOfBounds	; HL >= DE
+	cp	a			; ensure Z
+	ret
+.outOfBounds:
+	jp	unsetZ			; returns
+
 ; Read a byte in handle at (DE), put it into A and advance the handle's
 ; position.
 ; Z is set on success, unset if handle is at the end of the file.
-; TODO: detect end of file
 fsGetC:
+	call	fsHandleWithinBounds
+	jr	z, .proceed
+	; We want to unset Z, but also return 0 to ensure that a GetC that
+	; doesn't check Z doesn't end up with false data.
+	xor	a
+	jp	unsetZ		; returns
+.proceed:
 	push	ix
 	call	fsPlaceH
 	push	ix		; Save handle in IX for fsAdvanceH
@@ -514,3 +546,22 @@ fsOn:
 	pop	de
 	pop	hl
 	ret
+
+; Sets Z according to whether we have a filesystem mounted.
+fsIsOn:
+	; check whether (FS_GETC) is zero
+	push	hl
+	push	de
+	ld	hl, (FS_GETC)
+	ld	de, 0
+	call	cpHLDE
+	jr	nz, .mounted
+	; if equal, it means our FS is not mounted
+	call	unsetZ
+	jr	.end
+.mounted:
+	cp	a	; ensure Z
+.end:
+	pop	de
+	pop	hl
+	ret

tools/emul/user.h

@@ -20,3 +20,4 @@
 .equ    fsGetC         0x2d
 .equ    fsSeek         0x30
 .equ    fsTell         0x33
+.equ    cpHLDE         0x36

tools/emul/zasm/glue.asm

@@ -26,6 +26,7 @@ jp     fsOpen
 jp	fsGetC
 jp	fsSeek
 jp	fsTell
+jp	cpHLDE
 
 #include "core.asm"
 #include "parse.asm"

tools/tests/unit/test_core.asm

@@ -8,6 +8,7 @@ test:
 	ld	hl, 0xffff
 	ld	sp, hl
 
+	; *** subHL ***
 	ld	hl, 0x123
 	ld	a, 0x25
 	call	subHL
@@ -41,6 +42,26 @@ test:
 	jp	nz, fail
 	call	nexttest
 
+	; *** cpHLDE ***
+	ld	hl, 0x42
+	ld	de, 0x42
+	call	cpHLDE
+	jp	nz, fail
+	jp	c, fail
+	call	nexttest
+
+	ld	de, 0x4242
+	call	cpHLDE
+	jp	z, fail
+	jp	nc, fail
+	call	nexttest
+
+	ld	hl, 0x4243
+	call	cpHLDE
+	jp	z, fail
+	jp	c, fail
+	call	nexttest
+
 	; success
 	xor	a
 	halt

tools/tests/zasm/test7.asm

@@ -20,6 +20,7 @@
 .equ    fsGetC         0x2d
 .equ    fsSeek         0x30
 .equ    fsTell         0x33
+.equ    cpHLDE         0x36
 
 #include "zasm/const.asm"
 #include "zasm/util.asm"