add example and dev files to LodePNG repository

1 files changed, 653 insertions, 0 deletions

diff --git a/lodepng_util.cpp b/lodepng_util.cpp
new file mode 100644
index 0000000..3784b6e
--- /dev/null
+++ b/lodepng_util.cpp
@@ -0,0 +1,653 @@
+/*
+LodePNG Utils
+
+Copyright (c) 2005-2014 Lode Vandevenne
+
+This software is provided 'as-is', without any express or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+    1. The origin of this software must not be misrepresented; you must not
+    claim that you wrote the original software. If you use this software
+    in a product, an acknowledgment in the product documentation would be
+    appreciated but is not required.
+
+    2. Altered source versions must be plainly marked as such, and must not be
+    misrepresented as being the original software.
+
+    3. This notice may not be removed or altered from any source
+    distribution.
+*/
+
+#include "lodepng_util.h"
+#include <iostream>
+
+namespace lodepng
+{
+
+LodePNGInfo getPNGHeaderInfo(const std::vector<unsigned char>& png)
+{
+  unsigned w, h;
+  lodepng::State state;
+  lodepng_inspect(&w, &h, &state, &png[0], png.size());
+  return state.info_png;
+}
+
+unsigned getChunkInfo(std::vector<std::string>& names, std::vector<size_t>& sizes,
+                      const std::vector<unsigned char>& png)
+{
+  // Listing chunks is based on the original file, not the decoded png info.
+  const unsigned char *chunk, *begin, *end;
+  end = &png.back() + 1;
+  begin = chunk = &png.front() + 8;
+
+  while(chunk + 8 < end && chunk >= begin)
+  {
+    char type[5];
+    lodepng_chunk_type(type, chunk);
+    if(std::string(type).size() != 4) return 1;
+
+    names.push_back(type);
+    sizes.push_back(lodepng_chunk_length(chunk));
+
+    chunk = lodepng_chunk_next_const(chunk);
+  }
+  return 0;
+}
+
+unsigned getChunks(std::vector<std::string> names[3],
+                   std::vector<std::vector<unsigned char> > chunks[3],
+                   const std::vector<unsigned char>& png)
+{
+  const unsigned char *chunk, *next, *begin, *end;
+  end = &png.back() + 1;
+  begin = chunk = &png.front() + 8;
+
+  int location = 0;
+
+  while(chunk + 8 < end && chunk >= begin)
+  {
+    char type[5];
+    lodepng_chunk_type(type, chunk);
+    std::string name(type);
+    if(name.size() != 4) return 1;
+
+    next = lodepng_chunk_next_const(chunk);
+
+    if(name == "IHDR")
+    {
+      location = 0;
+    }
+    else if(name == "PLTE")
+    {
+      location = 1;
+    }
+    else if(name == "IDAT")
+    {
+      location = 2;
+    }
+    else if(name != "IEND")
+    {
+      names[location].push_back(name);
+      chunks[location].push_back(std::vector<unsigned char>(chunk, next));
+    }
+
+    chunk = next;
+  }
+  return 0;
+}
+
+
+unsigned insertChunks(std::vector<unsigned char>& png,
+                      const std::vector<std::vector<unsigned char> > chunks[3])
+{
+  const unsigned char *chunk, *next, *begin, *end;
+  end = &png.back() + 1;
+  begin = chunk = &png.front() + 8;
+
+  long l0 = 0; //location 0: IHDR-l0-PLTE (or IHDR-l0-l1-IDAT)
+  long l1 = 0; //location 1: PLTE-l1-IDAT (or IHDR-l0-l1-IDAT)
+  long l2 = 0; //location 2: IDAT-l2-IEND
+
+  while(chunk + 8 < end && chunk >= begin)
+  {
+    char type[5];
+    lodepng_chunk_type(type, chunk);
+    std::string name(type);
+    if(name.size() != 4) return 1;
+
+    next = lodepng_chunk_next_const(chunk);
+
+    if(name == "PLTE")
+    {
+      if(l0 == 0) l0 = chunk - begin + 8;
+    }
+    else if(name == "IDAT")
+    {
+      if(l0 == 0) l0 = chunk - begin + 8;
+      if(l1 == 0) l1 = chunk - begin + 8;
+    }
+    else if(name == "IEND")
+    {
+      if(l2 == 0) l2 = chunk - begin + 8;
+    }
+
+    chunk = next;
+  }
+
+  std::vector<unsigned char> result;
+  result.insert(result.end(), png.begin(), png.begin() + l0);
+  for(size_t i = 0; i < chunks[0].size(); i++) result.insert(result.end(), chunks[0][i].begin(), chunks[0][i].end());
+  result.insert(result.end(), png.begin() + l0, png.begin() + l1);
+  for(size_t i = 0; i < chunks[1].size(); i++) result.insert(result.end(), chunks[1][i].begin(), chunks[1][i].end());
+  result.insert(result.end(), png.begin() + l1, png.begin() + l2);
+  for(size_t i = 0; i < chunks[2].size(); i++) result.insert(result.end(), chunks[2][i].begin(), chunks[2][i].end());
+  result.insert(result.end(), png.begin() + l2, png.end());
+
+  png = result;
+  return 0;
+}
+
+unsigned getFilterTypesInterlaced(std::vector<std::vector<unsigned char> >& filterTypes,
+                                  const std::vector<unsigned char>& png)
+{
+  //Get color type and interlace type
+  lodepng::State state;
+  unsigned w, h;
+  unsigned error;
+  error = lodepng_inspect(&w, &h, &state, &png[0], png.size());
+
+  if(error) return 1;
+
+  //Read literal data from all IDAT chunks
+  const unsigned char *chunk, *begin, *end;
+  end = &png.back() + 1;
+  begin = chunk = &png.front() + 8;
+
+  std::vector<unsigned char> zdata;
+
+  while(chunk + 8 < end && chunk >= begin)
+  {
+    char type[5];
+    lodepng_chunk_type(type, chunk);
+    if(std::string(type).size() != 4) return 1; //Probably not a PNG file
+
+    if(std::string(type) == "IDAT")
+    {
+      const unsigned char* cdata = lodepng_chunk_data_const(chunk);
+      unsigned clength = lodepng_chunk_length(chunk);
+
+      for(unsigned i = 0; i < clength; i++)
+      {
+        zdata.push_back(cdata[i]);
+      }
+    }
+
+    chunk = lodepng_chunk_next_const(chunk);
+  }
+
+  //Decompress all IDAT data
+  std::vector<unsigned char> data;
+  error = lodepng::decompress(data, &zdata[0], zdata.size());
+
+  if(error) return 1;
+
+  if(state.info_png.interlace_method == 0)
+  {
+    filterTypes.resize(1);
+
+    //A line is 1 filter byte + all pixels
+    size_t linebytes = 1 + lodepng_get_raw_size(w, 1, &state.info_png.color);
+
+    for(size_t i = 0; i < data.size(); i += linebytes)
+    {
+      filterTypes[0].push_back(data[i]);
+    }
+  }
+  else
+  {
+    //Interlaced
+    filterTypes.resize(7);
+    static const unsigned ADAM7_IX[7] = { 0, 4, 0, 2, 0, 1, 0 }; /*x start values*/
+    static const unsigned ADAM7_IY[7] = { 0, 0, 4, 0, 2, 0, 1 }; /*y start values*/
+    static const unsigned ADAM7_DX[7] = { 8, 8, 4, 4, 2, 2, 1 }; /*x delta values*/
+    static const unsigned ADAM7_DY[7] = { 8, 8, 8, 4, 4, 2, 2 }; /*y delta values*/
+    size_t pos = 0;
+    for(size_t j = 0; j < 7; j++)
+    {
+      unsigned w2 = (w - ADAM7_IX[j] + ADAM7_DX[j] - 1) / ADAM7_DX[j];
+      unsigned h2 = (h - ADAM7_IY[j] + ADAM7_DY[j] - 1) / ADAM7_DY[j];
+      if(ADAM7_IX[j] >= w || ADAM7_IY[j] >= h) w2 = h2 = 0;
+      size_t linebytes = 1 + lodepng_get_raw_size(w2, 1, &state.info_png.color);
+      for(size_t i = 0; i < h2; i++)
+      {
+        filterTypes[j].push_back(data[pos]);
+        pos += linebytes;
+      }
+    }
+  }
+  return 0; /* OK */
+}
+
+
+unsigned getFilterTypes(std::vector<unsigned char>& filterTypes, const std::vector<unsigned char>& png)
+{
+  std::vector<std::vector<unsigned char> > passes;
+  unsigned error = getFilterTypesInterlaced(passes, png);
+  if(error) return error;
+
+  if(passes.size() == 1)
+  {
+    filterTypes.swap(passes[0]);
+  }
+  else
+  {
+    lodepng::State state;
+    unsigned w, h;
+    lodepng_inspect(&w, &h, &state, &png[0], png.size());
+    /*
+    Interlaced. Simplify it: put pass 6 and 7 alternating in the one vector so
+    that one filter per scanline of the uninterlaced image is given, with that
+    filter corresponding the closest to what it would be for non-interlaced
+    image.
+    */
+    for(size_t i = 0; i < h; i++)
+    {
+      filterTypes.push_back(i % 2 == 0 ? passes[5][i / 2] : passes[6][i / 2]);
+    }
+  }
+  return 0; /* OK */
+}
+
+int getPaletteValue(const unsigned char* data, size_t i, int bits)
+{
+  if(bits == 8) return data[i];
+  else if(bits == 4) return (data[i / 2] >> ((i % 2) * 4)) & 15;
+  else if(bits == 2) return (data[i / 4] >> ((i % 4) * 2)) & 3;
+  else if(bits == 1) return (data[i / 8] >> (i % 8)) & 1;
+  else return 0;
+}
+
+//This uses a stripped down version of picoPNG to extract detailed zlib information while decompressing.
+static const unsigned long LENBASE[29] =
+    {3,4,5,6,7,8,9,10,11,13,15,17,19,23,27,31,35,43,51,59,67,83,99,115,131,163,195,227,258};
+static const unsigned long LENEXTRA[29] =
+    {0,0,0,0,0,0,0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,  4,  5,  5,  5,  5,  0};
+static const unsigned long DISTBASE[30] =
+    {1,2,3,4,5,7,9,13,17,25,33,49,65,97,129,193,257,385,513,769,1025,1537,2049,3073,4097,6145,8193,12289,16385,24577};
+static const unsigned long DISTEXTRA[30] =
+    {0,0,0,0,1,1,2, 2, 3, 3, 4, 4, 5, 5,  6,  6,  7,  7,  8,  8,   9,   9,  10,  10,  11,  11,  12,   12,   13,   13};
+static const unsigned long CLCL[19] =
+    {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}; //code length code lengths
+
+struct ExtractZlib // Zlib decompression and information extraction
+{
+  std::vector<ZlibBlockInfo>* zlibinfo;
+  ExtractZlib(std::vector<ZlibBlockInfo>* info) : zlibinfo(info) {};
+  int error;
+
+  unsigned long readBitFromStream(size_t& bitp, const unsigned char* bits)
+  {
+    unsigned long result = (bits[bitp >> 3] >> (bitp & 0x7)) & 1;
+    bitp++;
+    return result;
+  }
+
+  unsigned long readBitsFromStream(size_t& bitp, const unsigned char* bits, size_t nbits)
+  {
+    unsigned long result = 0;
+    for(size_t i = 0; i < nbits; i++) result += (readBitFromStream(bitp, bits)) << i;
+    return result;
+  }
+
+  struct HuffmanTree
+  {
+    int makeFromLengths(const std::vector<unsigned long>& bitlen, unsigned long maxbitlen)
+    { //make tree given the lengths
+      unsigned long numcodes = (unsigned long)(bitlen.size()), treepos = 0, nodefilled = 0;
+      std::vector<unsigned long> tree1d(numcodes), blcount(maxbitlen + 1, 0), nextcode(maxbitlen + 1, 0);
+      //count number of instances of each code length
+      for(unsigned long bits = 0; bits < numcodes; bits++) blcount[bitlen[bits]]++;
+      for(unsigned long bits = 1; bits <= maxbitlen; bits++)
+      {
+        nextcode[bits] = (nextcode[bits - 1] + blcount[bits - 1]) << 1;
+      }
+      //generate all the codes
+      for(unsigned long n = 0; n < numcodes; n++) if(bitlen[n] != 0) tree1d[n] = nextcode[bitlen[n]]++;
+      tree2d.clear(); tree2d.resize(numcodes * 2, 32767); //32767 here means the tree2d isn't filled there yet
+      for(unsigned long n = 0; n < numcodes; n++) //the codes
+      for(unsigned long i = 0; i < bitlen[n]; i++) //the bits for this code
+      {
+        unsigned long bit = (tree1d[n] >> (bitlen[n] - i - 1)) & 1;
+        if(treepos > numcodes - 2) return 55;
+        if(tree2d[2 * treepos + bit] == 32767) //not yet filled in
+        {
+          if(i + 1 == bitlen[n])
+          {
+            //last bit
+            tree2d[2 * treepos + bit] = n;
+            treepos = 0;
+          }
+          else
+          {
+            //addresses are encoded as values > numcodes
+            tree2d[2 * treepos + bit] = ++nodefilled + numcodes;
+            treepos = nodefilled;
+          }
+        }
+        else treepos = tree2d[2 * treepos + bit] - numcodes; //subtract numcodes from address to get address value
+      }
+      return 0;
+    }
+    int decode(bool& decoded, unsigned long& result, size_t& treepos, unsigned long bit) const
+    { //Decodes a symbol from the tree
+      unsigned long numcodes = (unsigned long)tree2d.size() / 2;
+      if(treepos >= numcodes) return 11; //error: you appeared outside the codetree
+      result = tree2d[2 * treepos + bit];
+      decoded = (result < numcodes);
+      treepos = decoded ? 0 : result - numcodes;
+      return 0;
+    }
+    //2D representation of a huffman tree: one dimension is "0" or "1", the other contains all nodes and leaves.
+    std::vector<unsigned long> tree2d;
+  };
+
+  void inflate(std::vector<unsigned char>& out, const std::vector<unsigned char>& in, size_t inpos = 0)
+  {
+    size_t bp = 0, pos = 0; //bit pointer and byte pointer
+    error = 0;
+    unsigned long BFINAL = 0;
+    while(!BFINAL && !error)
+    {
+      size_t uncomprblockstart = pos;
+      size_t bpstart = bp;
+      if(bp >> 3 >= in.size()) { error = 52; return; } //error, bit pointer will jump past memory
+      BFINAL = readBitFromStream(bp, &in[inpos]);
+      unsigned long BTYPE = readBitFromStream(bp, &in[inpos]); BTYPE += 2 * readBitFromStream(bp, &in[inpos]);
+      zlibinfo->resize(zlibinfo->size() + 1);
+      zlibinfo->back().btype = BTYPE;
+      if(BTYPE == 3) { error = 20; return; } //error: invalid BTYPE
+      else if(BTYPE == 0) inflateNoCompression(out, &in[inpos], bp, pos, in.size());
+      else inflateHuffmanBlock(out, &in[inpos], bp, pos, in.size(), BTYPE);
+      size_t uncomprblocksize = pos - uncomprblockstart;
+      zlibinfo->back().compressedbits = bp - bpstart;
+      zlibinfo->back().uncompressedbytes = uncomprblocksize;
+    }
+  }
+
+  void generateFixedTrees(HuffmanTree& tree, HuffmanTree& treeD) //get the tree of a deflated block with fixed tree
+  {
+    std::vector<unsigned long> bitlen(288, 8), bitlenD(32, 5);;
+    for(size_t i = 144; i <= 255; i++) bitlen[i] = 9;
+    for(size_t i = 256; i <= 279; i++) bitlen[i] = 7;
+    tree.makeFromLengths(bitlen, 15);
+    treeD.makeFromLengths(bitlenD, 15);
+  }
+
+  //the code tree for Huffman codes, dist codes, and code length codes
+  HuffmanTree codetree, codetreeD, codelengthcodetree;
+  unsigned long huffmanDecodeSymbol(const unsigned char* in, size_t& bp, const HuffmanTree& tree, size_t inlength)
+  {
+    //decode a single symbol from given list of bits with given code tree. return value is the symbol
+    bool decoded; unsigned long ct;
+    for(size_t treepos = 0;;)
+    {
+      if((bp & 0x07) == 0 && (bp >> 3) > inlength) { error = 10; return 0; } //error: end reached without endcode
+      error = tree.decode(decoded, ct, treepos, readBitFromStream(bp, in));
+      if(error) return 0; //stop, an error happened
+      if(decoded) return ct;
+    }
+  }
+
+  void getTreeInflateDynamic(HuffmanTree& tree, HuffmanTree& treeD,
+                             const unsigned char* in, size_t& bp, size_t inlength)
+  {
+    size_t bpstart = bp;
+    //get the tree of a deflated block with dynamic tree, the tree itself is also Huffman compressed with a known tree
+    std::vector<unsigned long> bitlen(288, 0), bitlenD(32, 0);
+    if(bp >> 3 >= inlength - 2) { error = 49; return; } //the bit pointer is or will go past the memory
+    size_t HLIT =  readBitsFromStream(bp, in, 5) + 257; //number of literal/length codes + 257
+    size_t HDIST = readBitsFromStream(bp, in, 5) + 1; //number of dist codes + 1
+    size_t HCLEN = readBitsFromStream(bp, in, 4) + 4; //number of code length codes + 4
+    zlibinfo->back().hlit = HLIT - 257;
+    zlibinfo->back().hdist = HDIST - 1;
+    zlibinfo->back().hclen = HCLEN - 4;
+    std::vector<unsigned long> codelengthcode(19); //lengths of tree to decode the lengths of the dynamic tree
+    for(size_t i = 0; i < 19; i++) codelengthcode[CLCL[i]] = (i < HCLEN) ? readBitsFromStream(bp, in, 3) : 0;
+    //code length code lengths
+    for(size_t i = 0; i < codelengthcode.size(); i++) zlibinfo->back().clcl.push_back(codelengthcode[i]);
+    error = codelengthcodetree.makeFromLengths(codelengthcode, 7); if(error) return;
+    size_t i = 0, replength;
+    while(i < HLIT + HDIST)
+    {
+      unsigned long code = huffmanDecodeSymbol(in, bp, codelengthcodetree, inlength); if(error) return;
+      zlibinfo->back().treecodes.push_back(code); //tree symbol code
+      if(code <= 15)  { if(i < HLIT) bitlen[i++] = code; else bitlenD[i++ - HLIT] = code; } //a length code
+      else if(code == 16) //repeat previous
+      {
+        if(bp >> 3 >= inlength) { error = 50; return; } //error, bit pointer jumps past memory
+        replength = 3 + readBitsFromStream(bp, in, 2);
+        unsigned long value; //set value to the previous code
+        if((i - 1) < HLIT) value = bitlen[i - 1];
+        else value = bitlenD[i - HLIT - 1];
+        for(size_t n = 0; n < replength; n++) //repeat this value in the next lengths
+        {
+          if(i >= HLIT + HDIST) { error = 13; return; } //error: i is larger than the amount of codes
+          if(i < HLIT) bitlen[i++] = value; else bitlenD[i++ - HLIT] = value;
+        }
+      }
+      else if(code == 17) //repeat "0" 3-10 times
+      {
+        if(bp >> 3 >= inlength) { error = 50; return; } //error, bit pointer jumps past memory
+        replength = 3 + readBitsFromStream(bp, in, 3);
+        zlibinfo->back().treecodes.push_back(replength); //tree symbol code repetitions
+        for(size_t n = 0; n < replength; n++) //repeat this value in the next lengths
+        {
+          if(i >= HLIT + HDIST) { error = 14; return; } //error: i is larger than the amount of codes
+          if(i < HLIT) bitlen[i++] = 0; else bitlenD[i++ - HLIT] = 0;
+        }
+      }
+      else if(code == 18) //repeat "0" 11-138 times
+      {
+        if(bp >> 3 >= inlength) { error = 50; return; } //error, bit pointer jumps past memory
+        replength = 11 + readBitsFromStream(bp, in, 7);
+        zlibinfo->back().treecodes.push_back(replength); //tree symbol code repetitions
+        for(size_t n = 0; n < replength; n++) //repeat this value in the next lengths
+        {
+          if(i >= HLIT + HDIST) { error = 15; return; } //error: i is larger than the amount of codes
+          if(i < HLIT) bitlen[i++] = 0; else bitlenD[i++ - HLIT] = 0;
+        }
+      }
+      else { error = 16; return; } //error: somehow an unexisting code appeared. This can never happen.
+    }
+    if(bitlen[256] == 0) { error = 64; return; } //the length of the end code 256 must be larger than 0
+    error = tree.makeFromLengths(bitlen, 15);
+    if(error) return; //now we've finally got HLIT and HDIST, so generate the code trees, and the function is done
+    error = treeD.makeFromLengths(bitlenD, 15);
+    if(error) return;
+    zlibinfo->back().treebits = bp - bpstart;
+    //lit/len/end symbol lengths
+    for(size_t j = 0; j < bitlen.size(); j++) zlibinfo->back().litlenlengths.push_back(bitlen[j]);
+    //dist lengths
+    for(size_t j = 0; j < bitlenD.size(); j++) zlibinfo->back().distlengths.push_back(bitlenD[j]);
+  }
+
+  void inflateHuffmanBlock(std::vector<unsigned char>& out,
+                           const unsigned char* in, size_t& bp, size_t& pos, size_t inlength, unsigned long btype)
+  {
+    size_t numcodes = 0, numlit = 0, numlen = 0; //for logging
+    if(btype == 1) { generateFixedTrees(codetree, codetreeD); }
+    else if(btype == 2) { getTreeInflateDynamic(codetree, codetreeD, in, bp, inlength); if(error) return; }
+    for(;;)
+    {
+      unsigned long code = huffmanDecodeSymbol(in, bp, codetree, inlength); if(error) return;
+      numcodes++;
+      zlibinfo->back().lz77_lcode.push_back(code); //output code
+      zlibinfo->back().lz77_dcode.push_back(0);
+      zlibinfo->back().lz77_lbits.push_back(0);
+      zlibinfo->back().lz77_dbits.push_back(0);
+      zlibinfo->back().lz77_lvalue.push_back(0);
+      zlibinfo->back().lz77_dvalue.push_back(0);
+
+      if(code == 256) break; //end code
+      else if(code <= 255) //literal symbol
+      {
+        out.push_back((unsigned char)(code));
+        pos++;
+        numlit++;
+      }
+      else if(code >= 257 && code <= 285) //length code
+      {
+        size_t length = LENBASE[code - 257], numextrabits = LENEXTRA[code - 257];
+        if((bp >> 3) >= inlength) { error = 51; return; } //error, bit pointer will jump past memory
+        length += readBitsFromStream(bp, in, numextrabits);
+        unsigned long codeD = huffmanDecodeSymbol(in, bp, codetreeD, inlength); if(error) return;
+        if(codeD > 29) { error = 18; return; } //error: invalid dist code (30-31 are never used)
+        unsigned long dist = DISTBASE[codeD], numextrabitsD = DISTEXTRA[codeD];
+        if((bp >> 3) >= inlength) { error = 51; return; } //error, bit pointer will jump past memory
+        dist += readBitsFromStream(bp, in, numextrabitsD);
+        size_t start = pos, back = start - dist; //backwards
+        for(size_t i = 0; i < length; i++)
+        {
+          out.push_back(out[back++]);
+          pos++;
+          if(back >= start) back = start - dist;
+        }
+        numlen++;
+        zlibinfo->back().lz77_dcode.back() = codeD; //output distance code
+        zlibinfo->back().lz77_lbits.back() = numextrabits; //output length extra bits
+        zlibinfo->back().lz77_dbits.back() = numextrabitsD; //output dist extra bits
+        zlibinfo->back().lz77_lvalue.back() = length; //output length
+        zlibinfo->back().lz77_dvalue.back() = dist; //output dist
+      }
+    }
+    zlibinfo->back().numlit = numlit; //output number of literal symbols
+    zlibinfo->back().numlen = numlen; //output number of length symbols
+  }
+
+  void inflateNoCompression(std::vector<unsigned char>& out,
+                            const unsigned char* in, size_t& bp, size_t& pos, size_t inlength)
+  {
+    while((bp & 0x7) != 0) bp++; //go to first boundary of byte
+    size_t p = bp / 8;
+    if(p >= inlength - 4) { error = 52; return; } //error, bit pointer will jump past memory
+    unsigned long LEN = in[p] + 256u * in[p + 1], NLEN = in[p + 2] + 256u * in[p + 3]; p += 4;
+    if(LEN + NLEN != 65535) { error = 21; return; } //error: NLEN is not one's complement of LEN
+    if(p + LEN > inlength) { error = 23; return; } //error: reading outside of in buffer
+    for(unsigned long n = 0; n < LEN; n++)
+    {
+      out.push_back(in[p++]); //read LEN bytes of literal data
+      pos++;
+    }
+    bp = p * 8;
+  }
+
+  int decompress(std::vector<unsigned char>& out, const std::vector<unsigned char>& in) //returns error value
+  {
+    if(in.size() < 2) { return 53; } //error, size of zlib data too small
+    //error: 256 * in[0] + in[1] must be a multiple of 31, the FCHECK value is supposed to be made that way
+    if((in[0] * 256 + in[1]) % 31 != 0) { return 24; }
+    unsigned long CM = in[0] & 15, CINFO = (in[0] >> 4) & 15, FDICT = (in[1] >> 5) & 1;
+    //error: only compression method 8: inflate with sliding window of 32k is supported by the PNG spec
+    if(CM != 8 || CINFO > 7) { return 25; }
+    //error: the PNG spec says about the zlib stream: "The additional flags shall not specify a preset dictionary."
+    if(FDICT != 0) { return 26; }
+    inflate(out, in, 2);
+    return error; //note: adler32 checksum was skipped and ignored
+  }
+};
+
+struct ExtractPNG //PNG decoding and information extraction
+{
+  std::vector<ZlibBlockInfo>* zlibinfo;
+  ExtractPNG(std::vector<ZlibBlockInfo>* info) : zlibinfo(info) {};
+  int error;
+  void decode(const unsigned char* in, size_t size)
+  {
+    error = 0;
+    if(size == 0 || in == 0) { error = 48; return; } //the given data is empty
+    readPngHeader(&in[0], size); if(error) return;
+    size_t pos = 33; //first byte of the first chunk after the header
+    std::vector<unsigned char> idat; //the data from idat chunks
+    bool IEND = false;
+    //loop through the chunks, ignoring unknown chunks and stopping at IEND chunk.
+    //IDAT data is put at the start of the in buffer
+    while(!IEND)
+    {
+      //error: size of the in buffer too small to contain next chunk
+      if(pos + 8 >= size) { error = 30; return; }
+      size_t chunkLength = read32bitInt(&in[pos]); pos += 4;
+      if(chunkLength > 2147483647) { error = 63; return; }
+      //error: size of the in buffer too small to contain next chunk
+      if(pos + chunkLength >= size) { error = 35; return; }
+      //IDAT chunk, containing compressed image data
+      if(in[pos + 0] == 'I' && in[pos + 1] == 'D' && in[pos + 2] == 'A' && in[pos + 3] == 'T')
+      {
+        idat.insert(idat.end(), &in[pos + 4], &in[pos + 4 + chunkLength]);
+        pos += (4 + chunkLength);
+      }
+      else if(in[pos + 0] == 'I' && in[pos + 1] == 'E' && in[pos + 2] == 'N' && in[pos + 3] == 'D')
+      {
+          pos += 4;
+          IEND = true;
+      }
+      else //it's not an implemented chunk type, so ignore it: skip over the data
+      {
+        pos += (chunkLength + 4); //skip 4 letters and uninterpreted data of unimplemented chunk
+      }
+      pos += 4; //step over CRC (which is ignored)
+    }
+    std::vector<unsigned char> out; //now the out buffer will be filled
+    ExtractZlib zlib(zlibinfo); //decompress with the Zlib decompressor
+    error = zlib.decompress(out, idat);
+    if(error) return; //stop if the zlib decompressor returned an error
+  }
+
+  //read the information from the header and store it in the Info
+  void readPngHeader(const unsigned char* in, size_t inlength)
+  {
+    if(inlength < 29) { error = 27; return; } //error: the data length is smaller than the length of the header
+    if(in[0] != 137 || in[1] != 80 || in[2] != 78 || in[3] != 71
+    || in[4] != 13 || in[5] != 10 || in[6] != 26 || in[7] != 10) { error = 28; return; } //no PNG signature
+    //error: it doesn't start with a IHDR chunk!
+    if(in[12] != 'I' || in[13] != 'H' || in[14] != 'D' || in[15] != 'R') { error = 29; return; }
+  }
+
+  unsigned long readBitFromReversedStream(size_t& bitp, const unsigned char* bits)
+  {
+    unsigned long result = (bits[bitp >> 3] >> (7 - (bitp & 0x7))) & 1;
+    bitp++;
+    return result;
+  }
+
+  unsigned long readBitsFromReversedStream(size_t& bitp, const unsigned char* bits, unsigned long nbits)
+  {
+    unsigned long result = 0;
+    for(size_t i = nbits - 1; i < nbits; i--) result += ((readBitFromReversedStream(bitp, bits)) << i);
+    return result;
+  }
+
+  void setBitOfReversedStream(size_t& bitp, unsigned char* bits, unsigned long bit)
+  {
+    bits[bitp >> 3] |=  (bit << (7 - (bitp & 0x7))); bitp++;
+  }
+
+  unsigned long read32bitInt(const unsigned char* buffer)
+  {
+    return (unsigned int)((buffer[0] << 24u) | (buffer[1] << 16u) | (buffer[2] << 8u) | buffer[3]);
+  }
+};
+
+void extractZlibInfo(std::vector<ZlibBlockInfo>& zlibinfo, const std::vector<unsigned char>& in)
+{
+  ExtractPNG decoder(&zlibinfo);
+  decoder.decode(&in[0], in.size());
+
+  if(decoder.error) std::cout << "extract error: " << decoder.error << std::endl;
+}
+
+} // namespace lodepng