Fix sign and conversion warnings (major)

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.

1 files changed, 17 insertions, 7 deletions

diff --git a/libqpdf/BitStream.cc b/libqpdf/BitStream.cc
index bb52af31..95ca47c5 100644
--- a/libqpdf/BitStream.cc
+++ b/libqpdf/BitStream.cc
@@ -1,10 +1,11 @@
 #include <qpdf/BitStream.hh>
+#include <qpdf/QIntC.hh>
 
 // See comments in bits.cc
 #define BITS_READ 1
 #include "bits.icc"
 
-BitStream::BitStream(unsigned char const* p, int nbytes) :
+BitStream::BitStream(unsigned char const* p, size_t nbytes) :
     start(p),
     nbytes(nbytes)
 {
@@ -16,7 +17,7 @@ BitStream::reset()
 {
     p = start;
     bit_offset = 7;
-    if (static_cast<unsigned int>(nbytes) > static_cast<unsigned int>(-1) / 8)
+    if (QIntC::to_uint(nbytes) > static_cast<unsigned int>(-1) / 8)
     {
 	throw std::runtime_error("array too large for bitstream");
     }
@@ -24,21 +25,21 @@ BitStream::reset()
 }
 
 unsigned long long
-BitStream::getBits(int nbits)
+BitStream::getBits(size_t nbits)
 {
     return read_bits(this->p, this->bit_offset,
 		     this->bits_available, nbits);
 }
 
 long long
-BitStream::getBitsSigned(int nbits)
+BitStream::getBitsSigned(size_t nbits)
 {
     unsigned long long bits = read_bits(this->p, this->bit_offset,
                                         this->bits_available, nbits);
     long long result = 0;
-    if (static_cast<long long>(bits) > 1 << (nbits - 1))
+    if (static_cast<long long>(bits) > 1LL << (nbits - 1))
     {
-        result = static_cast<long long>(bits - (1 << nbits));
+        result = static_cast<long long>(bits -(1ULL << nbits));
     }
     else
     {
@@ -47,12 +48,21 @@ BitStream::getBitsSigned(int nbits)
     return result;
 }
 
+int
+BitStream::getBitsInt(size_t nbits)
+{
+    return static_cast<int>(
+        QIntC::to_uint(
+            read_bits(this->p, this->bit_offset,
+                      this->bits_available, nbits)));
+}
+
 void
 BitStream::skipToNextByte()
 {
     if (bit_offset != 7)
     {
-	unsigned int bits_to_skip = bit_offset + 1;
+	size_t bits_to_skip = bit_offset + 1;
 	if (bits_available < bits_to_skip)
 	{
 	    throw std::logic_error(