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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <knet.h>
include <mach.h>
include "fmio.h"
# FM_LFBINREAD -- Asynchronous blocked binary read from an lfile. We deal
# only with binary data here; unpacking of text must be done at a higher
# level. The basic procedure is to convert the indicated lfile segment into
# a range of lfile pages, then use the pagemap for the lfile to map these onto
# physical datafile pages. I/O is done in chunks of contiguous pages until
# the requested amount of data has been transferred.
procedure fm_lfbinread (lf, buf, maxbytes, offset)
pointer lf #I lfile descriptor
char buf[ARB] #O output data buffer
int maxbytes #I max bytes to read
long offset #I lfile offset
pointer fm, pm
int status, chan, nleft, szbpage
int l1,l2, p1,p2, d1,d2, op, nb, np
begin
fm = LF_FM(lf)
pm = LF_PAGEMAP(lf)
# Verify descriptor.
if (fm == NULL || pm == NULL) {
LF_STATUS(lf) = ERR
return
} else
LF_STATUS(lf) = 0
np = LF_NPAGES(lf)
chan = FM_CHAN(fm)
# Check that the read is in bounds.
nleft = min (offset + maxbytes, LF_FSIZE(lf) + 1) - offset
if (nleft <= 0)
return # read at EOF
# Map lfile offset,nbytes into a range of lfile pages.
# I/O transfers are required to be aligned on page boundaries.
# Note that less than full page may be transferred in a read.
szbpage = FM_SZBPAGE(fm)
l1 = (offset - 1) / szbpage + 1
l2 = l1 + ((nleft + szbpage-1) / szbpage) - 1
# Read the data from the physical datafile into the user buffer,
# mapping lfile pages to physical offsets and moving data in chunks
# of as many contiguous pages as possible.
op = 1
for (p1=l1; nleft > 0 && p1 <= l2; p1=p2) {
# Get a contiguous range of datafile pages.
d1 = Memi[pm+p1-1]
for (p2=p1+1; p2 <= l2; p2=p2+1) {
d2 = Memi[pm+p2-1]
if (d2 - d1 != p2 - p1)
break
}
# Read in the file segment.
nb = min (nleft, (p2 - p1) * szbpage)
call zardbf (chan, buf[op], nb, (d1-1)*szbpage + FM_DATASTART(fm))
LF_FLAGS(lf) = or (LF_FLAGS(lf), LFF_IOINPROGRESS)
LF_LTSIZE(lf) = nb
# Bump the i/o counters.
op = op + nb / SZB_CHAR
nleft = nleft - nb
# If we didn't read all the data, wait until the read completes.
if (nleft > 0) {
call zawtbf (chan, status)
LF_FLAGS(lf) = and (LF_FLAGS(lf), not(LFF_IOINPROGRESS))
if (status == ERR) {
LF_STATUS(lf) = ERR
return
} else if (status == 0) {
break
} else
LF_STATUS(lf) = LF_STATUS(lf) + status
}
}
end
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