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redo padding calculation for first half xref stream; old calculation

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failed to consider the effect of compressing the strema


git-svn-id: svn+q:///qpdf/trunk@932 71b93d88-0707-0410-a8cf-f5a4172ac649
This commit is contained in:
Jay Berkenbilt 2010-01-24 22:05:16 +00:00
parent 3416c60fe9
commit 05a6d9669d
1 changed files with 35 additions and 18 deletions
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49
libqpdf/QPDFWriter.cc
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@ -1734,14 +1734,15 @@ QPDFWriter::writeXRefStream(int objid, int max_id, int max_offset,
trailer_e which, int first, int last, int size)
{
return writeXRefStream(objid, max_id, max_offset,
which, first, last, size, 0, 0, 0, 0);
which, first, last, size, 0, 0, 0, 0, false);
}
int
QPDFWriter::writeXRefStream(int xref_id, int max_id, int max_offset,
trailer_e which, int first, int last, int size,
int prev, int hint_id,
int hint_offset, int hint_length)
int hint_offset, int hint_length,
bool skip_compression)
{
int xref_offset = this->pipeline->getCount();
int space_before_zero = xref_offset - 1;
@ -1764,8 +1765,14 @@ QPDFWriter::writeXRefStream(int xref_id, int max_id, int max_offset,
if (! ((this->stream_data_mode == qpdf_s_uncompress) || this->qdf_mode))
{
compressed = true;
if (! skip_compression)
{
// Write the stream dictionary for compression but don't
// actually compress. This helps us with computation of
// padding for pass 1 of linearization.
p = pushPipeline(
new Pl_Flate("compress xref", p, Pl_Flate::a_deflate));
}
p = pushPipeline(
new Pl_PNGFilter(
"pngify xref", p, Pl_PNGFilter::a_encode, esize, 0));
@ -2024,12 +2031,15 @@ QPDFWriter::writeLinearized()
// Must pad here too.
if (pass == 1)
{
// first_half_max_obj_offset is very likely to fall
// within the first 64K of the document (thus
// requiring two bytes for offsets) since it is the
// offset of the last uncompressed object in page 1.
// We allow for it to do otherwise though.
first_half_max_obj_offset = 65535;
// Set first_half_max_obj_offset to a value large
// enough to force four bytes to be reserved for each
// file offset. This would provide adequate space for
// the xref stream as long as the last object in page
// 1 starts with in the first 4 GB of the file, which
// is extremely likely. In the second pass, we will
// know the actual value for this, but it's okay if
// it's smaller.
first_half_max_obj_offset = 1 << 25;
}
pos = this->pipeline->getCount();
writeXRefStream(first_half_xref, first_half_end,
@ -2037,19 +2047,24 @@ QPDFWriter::writeLinearized()
t_lin_first, first_half_start, first_half_end,
first_trailer_size,
hint_length + second_xref_offset,
hint_id, hint_offset, hint_length);
hint_id, hint_offset, hint_length,
(pass == 1));
int endpos = this->pipeline->getCount();
if (pass == 1)
{
// Pad so we have enough room for the real xref
// stream. In an extremely unlikely worst case,
// first_half_max_obj_offset could be enough larger to
// require two extra bytes beyond what we calculated
// in pass 1. This means we need to save two extra
// bytes for each xref entry. To that, we'll add 10
// extra bytes for number length increases.
// stream. We've written the stream without
// compression (but with all the stream dictionary
// parameters to enable it) and assuming a very
// generous allowance for writing file offsets. We
// need a little extra padding to allow for zlib's
// output to be larger than its input (6 bytes plus 5
// bytes per 16K), and then we'll add 10 extra bytes
// for number length increases.
unsigned int xref_bytes = endpos - pos;
int possible_extra =
10 + (2 * (first_half_end - first_half_start + 1));
16 + (5 * ((xref_bytes + 16383) / 16384));
for (int i = 0; i < possible_extra; ++i)
{
writeString(" ");
@ -2064,6 +2079,8 @@ QPDFWriter::writeLinearized()
{
writeString(" ");
}
// A failure of this insertion means we didn't allow
// enough padding for the first pass xref stream.
assert(this->pipeline->getCount() == first_xref_end);
}
writeString("\n");