New function _dirskip that allows to skip an amount of bytes from the

directory with error check. git-svn-id: svn://svn.cc65.org/cc65/trunk@5668 b7a2c559-68d2-44c3-8de9-860c34a00d81
2012-06-01 19:23:34 +00:00
parent 8087959e18
commit eab5f250ad
5 changed files with 117 additions and 10 deletions
--- a/libsrc/cbm/dir.s
+++ b/libsrc/cbm/dir.s
@@ -0,0 +1,92 @@
+;
+; Ullrich von Bassewitz, 2012-06-01
+;
+; unsigned char __fastcall__ _dirskip (unsigned char count, struct DIR* dir);
+; /* Skip bytes from the directory and make sure, errno is set if this isn't
+;  * possible. Return true if anything is ok and false otherwise. For
+;  * simplicity we assume that read will never return less than count if there
+;  * is no error and end-of-file is not reached.
+;  * Note: count must not be more than 254.
+;  */
+;
+
+        .include        "dir.inc"
+        .include        "errno.inc"
+        .include        "zeropage.inc"
+
+        .import         _read
+        .import         pushax, pushptr1idx
+        .import         subysp, addysp1
+
+
+.proc   __dirskip
+
+        sta     ptr1
+        stx     ptr1+1          ; Save dir
+
+; Get count and allocate space on the stack
+
+        ldy     #0
+        lda     (sp),y
+        pha
+        tay
+        jsr     subysp
+
+; Save current value of sp
+
+        lda     sp
+        pha
+        lda     sp+1
+        pha
+
+; Push dir->fd
+
+        ldy     #DIR::fd+1
+        jsr     pushptr1idx
+
+; Push pointer to buffer
+
+        pla
+        tax
+        pla
+        jsr     pushax
+
+; Load count and call read
+
+        pla
+        pha
+        ldx     #0
+        jsr     _read
+
+; Check for errors. In case of errors, errno is already set.
+
+        cpx     #$FF
+        bne     L2
+
+; read() returned an error
+
+        pla                     ; Count
+        tay
+        lda     #0
+        tax
+L1:     jmp     addysp1         ; Drop buffer plus count
+
+; read() was successful, check number of bytes read. We assume that read will
+; not return more than count, so X is zero if we come here.
+
+L2:     sta     tmp1
+        pla                     ; count
+        tay
+        cmp     tmp1
+        beq     L1              ; Drop variables, return count
+
+; Didn't read enough bytes. This is an error for us, but errno is not set
+
+        lda     #<EIO
+        sta     __errno
+        stx     __errno+1
+        txa                     ; A=X=0
+        beq     L1              ; Branch always
+
+.endproc
+