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SDFI, SDFO–System Data Format I/O Routines
The SDFIOA$ entry point is the same as SDFIO$ except that the calling program can
specify a word offset into the initial read sector address. This allows SDFI to begin
reading on a word boundary instead of a sector boundary. The word offset must be in
the range of 0 through 27. If the word offset is 0, SDFIOA$ performs the same as
SDFIO$.
Calling Sequence for SDFIO$
Auto Switch Common Bank or Relocatable Relocatable
L,U A0,address-of-packet
LMJ X11,CBSDFIO$-1
error return
normal return
Calling Sequence for SDFIOA$
L,U A0,address-of-packet
I$BJ X11,CBSDFIO$
error return
normal return
L,U A0,address-of-packet
LMJ X11,SDFIO$
error return
normal return
Auto Switch Common Bank or Relocatable Relocatable
L,U A0,address-of-packet
L A1,word-offset
LMJ X11,CBSDFIOA$-1
error return
normal return
L,U A0,address-of-packet
L A1,word-offset
I$BJ X11,CBSDFIOA$
error return
normal return
L,U A0,address-of-packet
L A1,word-offset
LMJ X11,SDFIOA$
error return
normal return
If SDFI takes the error return, register A4 contains the error code. See 21.3 for an
explanation of error codes.
If SDFI takes the normal return, SDFI is opened and ready to read images.
21.1.2.2. Read an Image
Each call to SDFI$ or SDFINT$ reads one image from the file or element. SDFI returns
the image in the image buffer and returns the image control word (ICW) in word 10 of
the packet. There are two entry points to read an image.
SDFI$ read an image (truncation if image overflows image buffer)
SDFINT$ read an image (no truncation)
The only difference between SDFI$ and SDFINT$ is how they handle an image buffer
overflow. The SDFI$ entry point truncates images that are too long to fit in the image
buffer. The image buffer is filled, and the rest of the image is lost. SDFI returns the total
length of the image in word 10 (T1) of the FCT if the image is truncated. Therefore, the
caller may detect if an image was truncated by checking whether the image length
returned in word 10 (T1) of the FCT is greater than the image buffer length.
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