On (13 Jun 97) Kurt Wismer wrote to All...
 KW> ok, can someone tell me what i'm doing wrong here? the problematic
 KW> behaviour is described below...
I see a couple of problems, though I'm not sure if they're related to
the symptoms you're seeing or not.
 KW>    inc dx                   ;move sector pointer forward by 1
 KW>    mov cx, 1h               ;read 1 sector
 KW>    mov bx, offset buff      ;set read buffer
 KW>    int 25h                  ;absolute disk read cx sectors starting
 KW>                             ;at dx
int 25h leaves an extra word on the stack - if you don't get rid of it
(typically by popping it into a register) you'll eventually run into
problems.
 KW>    jc close                 ;close and exit on error
 KW>    mov bx, offset buff      ;prep buffer for comparison
 KW>    mov cx, 200h             ;200h byte string comparisons between
 KW> buffer
 KW> loop1:
 KW>    cmp byte ptr[bx], 0f6h   ;compare the sector to the hex byte f6
 KW> (empty)
 KW>    jne writ                 ;write sector at first instance of a
 KW> difference
 KW>    inc bx
 KW>    loop loop1
 KW>    jmp arge                 ;skip sector save routine if the sector is
 KW>                             ;full of f6h's
This isn't a bug as such, but I'd rewrite this loop:
    mov si, offset buff
    mov cx, 100h
loop1:
    lodsw
    cmp ax, 0f6f6h
    loopz   loop1
The conditional forms of `loop' are _really_ handy instructions at
times.  Doing comparisons on words instead of bytes should roughly
double the overall speed as well.
 KW> writ:
 KW>    push dx                  ;save sector index
 KW>    mov bx, offset buff + 200h    ;append sector index to buffered
 KW>    mov byte ptr[bx], dh          ;sector for later recovery
 KW>    mov byte ptr[bx + 1], dl
Umm...unless I'm mistaken, this is overwriting the last byte of the
sector with the first byte of the sector index number.
 KW> buff db 202 dup(?)
In your program you're using 202 HEX bytes, but you're only reserving
202 DECIMAL bytes for the buffer...
    Later,
    Jerry.
... The Universe is a figment of its own imagination.
--- PPoint 1.90
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