Add signed support to BitStream and BitWriter

4 files changed, 36 insertions, 0 deletions

diff --git a/libqpdf/BitStream.cc b/libqpdf/BitStream.cc
index 14eae55d..bb52af31 100644
--- a/libqpdf/BitStream.cc
+++ b/libqpdf/BitStream.cc
@@ -30,6 +30,23 @@ BitStream::getBits(int nbits)
 		     this->bits_available, nbits);
 }
 
+long long
+BitStream::getBitsSigned(int 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))
+    {
+        result = static_cast<long long>(bits - (1 << nbits));
+    }
+    else
+    {
+        result = static_cast<long long>(bits);
+    }
+    return result;
+}
+
 void
 BitStream::skipToNextByte()
 {
diff --git a/libqpdf/BitWriter.cc b/libqpdf/BitWriter.cc
index 4fb375cb..7513ac76 100644
--- a/libqpdf/BitWriter.cc
+++ b/libqpdf/BitWriter.cc
@@ -18,6 +18,21 @@ BitWriter::writeBits(unsigned long long val, unsigned int bits)
 }
 
 void
+BitWriter::writeBitsSigned(long long val, unsigned int bits)
+{
+    unsigned long long uval = 0;
+    if (val < 0)
+    {
+        uval = static_cast<unsigned long long>((1 << bits) + val);
+    }
+    else
+    {
+        uval = static_cast<unsigned long long>(val);
+    }
+    writeBits(uval, bits);
+}
+
+void
 BitWriter::flush()
 {
     if (bit_offset < 7)
diff --git a/libqpdf/qpdf/BitStream.hh b/libqpdf/qpdf/BitStream.hh
index e45a90ee..8ea8bec4 100644
--- a/libqpdf/qpdf/BitStream.hh
+++ b/libqpdf/qpdf/BitStream.hh
@@ -15,6 +15,8 @@ class BitStream
     QPDF_DLL
     unsigned long long getBits(int nbits);
     QPDF_DLL
+    long long getBitsSigned(int nbits);
+    QPDF_DLL
     void skipToNextByte();
 
   private:
diff --git a/libqpdf/qpdf/BitWriter.hh b/libqpdf/qpdf/BitWriter.hh
index 7e3b07a9..3d93c0b7 100644
--- a/libqpdf/qpdf/BitWriter.hh
+++ b/libqpdf/qpdf/BitWriter.hh
@@ -16,6 +16,8 @@ class BitWriter
     BitWriter(Pipeline* pl);
     QPDF_DLL
     void writeBits(unsigned long long val, unsigned int bits);
+    QPDF_DLL
+    void writeBitsSigned(long long val, unsigned int bits);
     // Force any partial byte to be written to the pipeline.
     QPDF_DLL
     void flush();