// Copyright (C) 2004-2021 Artifex Software, Inc.

//

// This file is part of MuPDF.

//

// MuPDF is free software: you can redistribute it and/or modify it under the

// terms of the GNU Affero General Public License as published by the Free

// Software Foundation, either version 3 of the License, or (at your option)

// any later version.

//

// MuPDF is distributed in the hope that it will be useful, but WITHOUT ANY

// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS

// FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more

// details.

//

// You should have received a copy of the GNU Affero General Public License

// along with MuPDF. If not, see <https://www.gnu.org/licenses/agpl-3.0.en.html>

//

// Alternative licensing terms are available from the licensor.

// For commercial licensing, see <https://www.artifex.com/> or contact

// Artifex Software, Inc., 39 Mesa Street, Suite 108A, San Francisco,

// CA 94129, USA, for further information.

#include "mupdf/fitz.h"

#include "pixmap-imp.h"

#include <string.h>

#include <limits.h>

struct info

{

  int gif89a;

  unsigned int width, height;

  unsigned char aspect;

  unsigned int xres, yres;

  unsigned int image_left, image_top;

  unsigned int image_width, image_height;

  unsigned int image_interlaced;

  int has_gct;

  int gct_entries;

  unsigned char *gct;

  unsigned int gct_background;

  int has_lct;

  int lct_entries;

  unsigned char *lct;

  int has_transparency;

  unsigned int transparent;

  unsigned char *mask;

  fz_pixmap *pix;

};

/* default color table, where the first two entries are black and white */

static const unsigned char dct[256 * 3] = {

  0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02,

  0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x05, 0x05, 0x05, 0x06, 0x06, 0x06,

  0x07, 0x07, 0x07, 0x08, 0x08, 0x08, 0x09, 0x09, 0x09, 0x0a, 0x0a, 0x0a,

  0x0b, 0x0b, 0x0b, 0x0c, 0x0c, 0x0c, 0x0d, 0x0d, 0x0d, 0x0e, 0x0e, 0x0e,

  0x0f, 0x0f, 0x0f, 0x10, 0x10, 0x10, 0x11, 0x11, 0x11, 0x12, 0x12, 0x12,

  0x13, 0x13, 0x13, 0x14, 0x14, 0x14, 0x15, 0x15, 0x15, 0x16, 0x16, 0x16,

  0x17, 0x17, 0x17, 0x18, 0x18, 0x18, 0x19, 0x19, 0x19, 0x1a, 0x1a, 0x1a,

  0x1b, 0x1b, 0x1b, 0x1c, 0x1c, 0x1c, 0x1d, 0x1d, 0x1d, 0x1e, 0x1e, 0x1e,

  0x1f, 0x1f, 0x1f, 0x20, 0x20, 0x20, 0x21, 0x21, 0x21, 0x22, 0x22, 0x22,

  0x23, 0x23, 0x23, 0x24, 0x24, 0x24, 0x25, 0x25, 0x25, 0x26, 0x26, 0x26,

  0x27, 0x27, 0x27, 0x28, 0x28, 0x28, 0x29, 0x29, 0x29, 0x2a, 0x2a, 0x2a,

  0x2b, 0x2b, 0x2b, 0x2c, 0x2c, 0x2c, 0x2d, 0x2d, 0x2d, 0x2e, 0x2e, 0x2e,

  0x2f, 0x2f, 0x2f, 0x30, 0x30, 0x30, 0x31, 0x31, 0x31, 0x32, 0x32, 0x32,

  0x33, 0x33, 0x33, 0x34, 0x34, 0x34, 0x35, 0x35, 0x35, 0x36, 0x36, 0x36,

  0x37, 0x37, 0x37, 0x38, 0x38, 0x38, 0x39, 0x39, 0x39, 0x3a, 0x3a, 0x3a,

  0x3b, 0x3b, 0x3b, 0x3c, 0x3c, 0x3c, 0x3d, 0x3d, 0x3d, 0x3e, 0x3e, 0x3e,

  0x3f, 0x3f, 0x3f, 0x40, 0x40, 0x40, 0x41, 0x41, 0x41, 0x42, 0x42, 0x42,

  0x43, 0x43, 0x43, 0x44, 0x44, 0x44, 0x45, 0x45, 0x45, 0x46, 0x46, 0x46,

  0x47, 0x47, 0x47, 0x48, 0x48, 0x48, 0x49, 0x49, 0x49, 0x4a, 0x4a, 0x4a,

  0x4b, 0x4b, 0x4b, 0x4c, 0x4c, 0x4c, 0x4d, 0x4d, 0x4d, 0x4e, 0x4e, 0x4e,

  0x4f, 0x4f, 0x4f, 0x50, 0x50, 0x50, 0x51, 0x51, 0x51, 0x52, 0x52, 0x52,

  0x53, 0x53, 0x53, 0x54, 0x54, 0x54, 0x55, 0x55, 0x55, 0x56, 0x56, 0x56,

  0x57, 0x57, 0x57, 0x58, 0x58, 0x58, 0x59, 0x59, 0x59, 0x5a, 0x5a, 0x5a,

  0x5b, 0x5b, 0x5b, 0x5c, 0x5c, 0x5c, 0x5d, 0x5d, 0x5d, 0x5e, 0x5e, 0x5e,

  0x5f, 0x5f, 0x5f, 0x60, 0x60, 0x60, 0x61, 0x61, 0x61, 0x62, 0x62, 0x62,

  0x63, 0x63, 0x63, 0x64, 0x64, 0x64, 0x65, 0x65, 0x65, 0x66, 0x66, 0x66,

  0x67, 0x67, 0x67, 0x68, 0x68, 0x68, 0x69, 0x69, 0x69, 0x6a, 0x6a, 0x6a,

  0x6b, 0x6b, 0x6b, 0x6c, 0x6c, 0x6c, 0x6d, 0x6d, 0x6d, 0x6e, 0x6e, 0x6e,

  0x6f, 0x6f, 0x6f, 0x70, 0x70, 0x70, 0x71, 0x71, 0x71, 0x72, 0x72, 0x72,

  0x73, 0x73, 0x73, 0x74, 0x74, 0x74, 0x75, 0x75, 0x75, 0x76, 0x76, 0x76,

  0x77, 0x77, 0x77, 0x78, 0x78, 0x78, 0x79, 0x79, 0x79, 0x7a, 0x7a, 0x7a,

  0x7b, 0x7b, 0x7b, 0x7c, 0x7c, 0x7c, 0x7d, 0x7d, 0x7d, 0x7e, 0x7e, 0x7e,

  0x7f, 0x7f, 0x7f, 0x80, 0x80, 0x80, 0x81, 0x81, 0x81, 0x82, 0x82, 0x82,

  0x83, 0x83, 0x83, 0x84, 0x84, 0x84, 0x85, 0x85, 0x85, 0x86, 0x86, 0x86,

  0x87, 0x87, 0x87, 0x88, 0x88, 0x88, 0x89, 0x89, 0x89, 0x8a, 0x8a, 0x8a,

  0x8b, 0x8b, 0x8b, 0x8c, 0x8c, 0x8c, 0x8d, 0x8d, 0x8d, 0x8e, 0x8e, 0x8e,

  0x8f, 0x8f, 0x8f, 0x90, 0x90, 0x90, 0x91, 0x91, 0x91, 0x92, 0x92, 0x92,

  0x93, 0x93, 0x93, 0x94, 0x94, 0x94, 0x95, 0x95, 0x95, 0x96, 0x96, 0x96,

  0x97, 0x97, 0x97, 0x98, 0x98, 0x98, 0x99, 0x99, 0x99, 0x9a, 0x9a, 0x9a,

  0x9b, 0x9b, 0x9b, 0x9c, 0x9c, 0x9c, 0x9d, 0x9d, 0x9d, 0x9e, 0x9e, 0x9e,

  0x9f, 0x9f, 0x9f, 0xa0, 0xa0, 0xa0, 0xa1, 0xa1, 0xa1, 0xa2, 0xa2, 0xa2,

  0xa3, 0xa3, 0xa3, 0xa4, 0xa4, 0xa4, 0xa5, 0xa5, 0xa5, 0xa6, 0xa6, 0xa6,

  0xa7, 0xa7, 0xa7, 0xa8, 0xa8, 0xa8, 0xa9, 0xa9, 0xa9, 0xaa, 0xaa, 0xaa,

  0xab, 0xab, 0xab, 0xac, 0xac, 0xac, 0xad, 0xad, 0xad, 0xae, 0xae, 0xae,

  0xaf, 0xaf, 0xaf, 0xb0, 0xb0, 0xb0, 0xb1, 0xb1, 0xb1, 0xb2, 0xb2, 0xb2,

  0xb3, 0xb3, 0xb3, 0xb4, 0xb4, 0xb4, 0xb5, 0xb5, 0xb5, 0xb6, 0xb6, 0xb6,

  0xb7, 0xb7, 0xb7, 0xb8, 0xb8, 0xb8, 0xb9, 0xb9, 0xb9, 0xba, 0xba, 0xba,

  0xbb, 0xbb, 0xbb, 0xbc, 0xbc, 0xbc, 0xbd, 0xbd, 0xbd, 0xbe, 0xbe, 0xbe,

  0xbf, 0xbf, 0xbf, 0xc0, 0xc0, 0xc0, 0xc1, 0xc1, 0xc1, 0xc2, 0xc2, 0xc2,

  0xc3, 0xc3, 0xc3, 0xc4, 0xc4, 0xc4, 0xc5, 0xc5, 0xc5, 0xc6, 0xc6, 0xc6,

  0xc7, 0xc7, 0xc7, 0xc8, 0xc8, 0xc8, 0xc9, 0xc9, 0xc9, 0xca, 0xca, 0xca,

  0xcb, 0xcb, 0xcb, 0xcc, 0xcc, 0xcc, 0xcd, 0xcd, 0xcd, 0xce, 0xce, 0xce,

  0xcf, 0xcf, 0xcf, 0xd0, 0xd0, 0xd0, 0xd1, 0xd1, 0xd1, 0xd2, 0xd2, 0xd2,

  0xd3, 0xd3, 0xd3, 0xd4, 0xd4, 0xd4, 0xd5, 0xd5, 0xd5, 0xd6, 0xd6, 0xd6,

  0xd7, 0xd7, 0xd7, 0xd8, 0xd8, 0xd8, 0xd9, 0xd9, 0xd9, 0xda, 0xda, 0xda,

  0xdb, 0xdb, 0xdb, 0xdc, 0xdc, 0xdc, 0xdd, 0xdd, 0xdd, 0xde, 0xde, 0xde,

  0xdf, 0xdf, 0xdf, 0xe0, 0xe0, 0xe0, 0xe1, 0xe1, 0xe1, 0xe2, 0xe2, 0xe2,

  0xe3, 0xe3, 0xe3, 0xe4, 0xe4, 0xe4, 0xe5, 0xe5, 0xe5, 0xe6, 0xe6, 0xe6,

  0xe7, 0xe7, 0xe7, 0xe8, 0xe8, 0xe8, 0xe9, 0xe9, 0xe9, 0xea, 0xea, 0xea,

  0xeb, 0xeb, 0xeb, 0xec, 0xec, 0xec, 0xed, 0xed, 0xed, 0xee, 0xee, 0xee,

  0xef, 0xef, 0xef, 0xf0, 0xf0, 0xf0, 0xf1, 0xf1, 0xf1, 0xf2, 0xf2, 0xf2,

  0xf3, 0xf3, 0xf3, 0xf4, 0xf4, 0xf4, 0xf5, 0xf5, 0xf5, 0xf6, 0xf6, 0xf6,

  0xf7, 0xf7, 0xf7, 0xf8, 0xf8, 0xf8, 0xf9, 0xf9, 0xf9, 0xfa, 0xfa, 0xfa,

  0xfb, 0xfb, 0xfb, 0xfc, 0xfc, 0xfc, 0xfd, 0xfd, 0xfd, 0xfe, 0xfe, 0xfe,

};

static const unsigned char *

gif_read_subblocks(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end, fz_buffer *buf)

{

  int len;

  do

  {

    if (end - p < 1)

      fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in data subblocks in gif image");

    len = *p;

    p += 1;

    if (len > 0)

    {

      if (end - p < len)

        fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in data subblock in gif image");

      if (buf)

        fz_append_data(ctx, buf, p, len);

      p += len;

    }

  } while (len > 0);

  return p;

}

static const unsigned char *

gif_read_header(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < 6)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in header in gif image");

  if (memcmp(&p[0], "GIF", 3))

    fz_throw(ctx, FZ_ERROR_FORMAT, "invalid signature in gif image");

  if (memcmp(&p[3], "87a", 3) && memcmp(&p[3], "89a", 3))

    fz_throw(ctx, FZ_ERROR_FORMAT, "unsupported version in gif image");

  info->gif89a = !memcmp(p, "GIF89a", 6);

  return p + 6;

}

/* coverity[-tainted_data_return] */

static unsigned int

safe_load_u16(const unsigned char *p)

{

  return p[1] << 8 | p[0];

}

static const unsigned char *

gif_read_lsd(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < 7)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in logical screen descriptor in gif image");

  info->width = safe_load_u16(p);

  info->height = safe_load_u16(p+2);

  if (info->width <= 0)

    fz_throw(ctx, FZ_ERROR_FORMAT, "image width must be > 0");

  if (info->height <= 0)

    fz_throw(ctx, FZ_ERROR_FORMAT, "image height must be > 0");

  if (info->height > UINT_MAX / info->width / 3 /* components */)

    fz_throw(ctx, FZ_ERROR_LIMIT, "image dimensions might overflow");

  info->has_gct = (p[4] >> 7) & 0x1;

  if (info->has_gct)

  {

    info->gct_entries = 1 << ((p[4] & 0x7) + 1);

    info->gct_background = fz_clampi(p[5], 0, info->gct_entries - 1);

  }

  info->aspect = p[6];

  info->xres = 96;

  info->yres = 96;

  if (info->aspect > 0)

    info->yres = (((float) info->aspect + 15) / 64) * 96;

  return p + 7;

}

static const unsigned char *

gif_read_gct(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < info->gct_entries * 3)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in global color table in gif image");

  info->gct = Memento_label(fz_malloc(ctx, info->gct_entries * 3), "gif_gct");

  memmove(info->gct, p, info->gct_entries * 3);

  return p + info->gct_entries * 3;

}

static const unsigned char *

gif_read_id(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < 10)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in image descriptor in gif image");

  info->image_left = p[2] << 8 | p[1];

  info->image_top = p[4] << 8 | p[3];

  info->image_width = p[6] << 8 | p[5];

  info->image_height = p[8] << 8 | p[7];

  info->has_lct = (p[9] >> 7) & 0x1;

  info->image_interlaced = (p[9] >> 6) & 0x1;

  if (info->has_lct)

    info->lct_entries = 1 << ((p[9] & 0x7) + 1);

  return p + 10;

}

static const unsigned char *

gif_read_lct(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < info->lct_entries * 3)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in local color table in gif image");

  info->lct = Memento_label(fz_malloc(ctx, info->lct_entries * 3), "gif_lct");

  memmove(info->lct, p, info->lct_entries * 3);

  return p + info->lct_entries * 3;

}

static void

gif_read_line(fz_context *ctx, struct info *info, int ct_entries, const unsigned char *ct, unsigned int y, unsigned char *sp)

{

  unsigned int index = (info->image_top + y) * info->width + info->image_left;

  unsigned char *samples = fz_pixmap_samples(ctx, info->pix);

  unsigned char *dp = &samples[index * 4];

  unsigned char *mp = &info->mask[index];

  unsigned int x, k;

  if (info->image_top + y >= info->height)

    return;

  for (x = 0; x < info->image_width && info->image_left + x < info->width; x++, sp++, mp++, dp += 4)

    if (!info->has_transparency || *sp != info->transparent)

    {

      *mp = 0x02;

      for (k = 0; k < 3; k++)

        dp[k] = ct[fz_clampi(*sp, 0, ct_entries - 1) * 3 + k];

      dp[3] = 255;

    }

    else if (*mp == 0x01)

      *mp = 0x00;

}

static const unsigned char *

gif_read_tbid(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  fz_stream *stm = NULL, *lzwstm = NULL;

  unsigned int mincodesize, y;

  fz_buffer *compressed = NULL, *uncompressed = NULL;

  const unsigned char *ct;

  unsigned char *sp;

  int ct_entries;

  if (end - p < 1)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in table based image data in gif image");

  mincodesize = *p;

  /* if there is no overlap, avoid pasting image data, just consume it */

  if (info->image_top >= info->height || info->image_left >= info->width)

  {

    p = gif_read_subblocks(ctx, info, p + 1, end, NULL);

    return p;

  }

  fz_var(compressed);

  fz_var(lzwstm);

  fz_var(stm);

  fz_var(uncompressed);

  fz_try(ctx)

  {

    compressed = fz_new_buffer(ctx, 0);

    p = gif_read_subblocks(ctx, info, p + 1, end, compressed);

    stm = fz_open_buffer(ctx, compressed);

    lzwstm = fz_open_lzwd(ctx, stm, 0, mincodesize + 1, 1, 1);

    uncompressed = fz_read_all(ctx, lzwstm, 0);

    if (uncompressed->len < (size_t)info->image_width * info->image_height)

    {

      fz_warn(ctx, "premature end in compressed table based image data in gif image");

      while (uncompressed->len < (size_t)info->image_width * info->image_height)

        fz_append_byte(ctx, uncompressed, 0x00);

    }

    if (info->has_lct)

    {

      ct = info->lct;

      ct_entries = info->lct_entries;

    }

    else if (info->has_gct)

    {

      ct = info->gct;

      ct_entries = info->gct_entries;

    }

    else

    {

      ct = dct;

      ct_entries = 256;

    }

    sp = uncompressed->data;

    if (info->image_interlaced)

    {

      for (y = 0; y < info->image_height; y += 8, sp += info->image_width)

        gif_read_line(ctx, info, ct_entries, ct, y, sp);

      for (y = 4; y < info->image_height; y += 8, sp += info->image_width)

        gif_read_line(ctx, info, ct_entries, ct, y, sp);

      for (y = 2; y < info->image_height; y += 4, sp += info->image_width)

        gif_read_line(ctx, info, ct_entries, ct, y, sp);

      for (y = 1; y < info->image_height; y += 2, sp += info->image_width)

        gif_read_line(ctx, info, ct_entries, ct, y, sp);

    }

    else

      for (y = 0; y < info->image_height; y++, sp += info->image_width)

        gif_read_line(ctx, info, ct_entries, ct, y, sp);

  }

  fz_always(ctx)

  {

    fz_drop_buffer(ctx, uncompressed);

    fz_drop_buffer(ctx, compressed);

    fz_drop_stream(ctx, lzwstm);

    fz_drop_stream(ctx, stm);

  }

  fz_catch(ctx)

  {

    fz_rethrow(ctx);

  }

  return p;

}

static const unsigned char *

gif_read_gce(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < 8)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in graphic control extension in gif image");

  if (p[2] != 0x04)

    fz_throw(ctx, FZ_ERROR_FORMAT, "out of range graphic control extension block size in gif image");

  info->has_transparency = p[3] & 0x1;

  if (info->has_transparency)

    info->transparent = p[6];

  return p + 8;

}

static const unsigned char *

gif_read_ce(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  return gif_read_subblocks(ctx, info, p + 2, end, NULL);

}

static const unsigned char*

gif_read_pte(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  if (end - p < 15)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in plain text extension in gif image");

  if (p[2] != 0x0c)

    fz_throw(ctx, FZ_ERROR_FORMAT, "out of range plain text extension block size in gif image");

  return gif_read_subblocks(ctx, info, p + 15, end, NULL);

}

static const unsigned char *

gif_read_icc(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

#if FZ_ENABLE_ICC

  fz_colorspace *icc = NULL;

  fz_buffer *buf = NULL;

  fz_var(p);

  buf = fz_new_buffer(ctx, 0);

  fz_try(ctx)

  {

    p = gif_read_subblocks(ctx, info, p, end, buf);

    icc = fz_new_icc_colorspace(ctx, FZ_COLORSPACE_RGB, 0, NULL, buf);

    fz_drop_colorspace(ctx, info->pix->colorspace);

    info->pix->colorspace = icc;

  }

  fz_always(ctx)

    fz_drop_buffer(ctx, buf);

  fz_catch(ctx)

  {

    fz_rethrow_if(ctx, FZ_ERROR_SYSTEM);

    fz_report_error(ctx);

    fz_warn(ctx, "ignoring embedded ICC profile in GIF");

  }

  return p;

#else

  return gif_read_subblocks(ctx, info, p, end, NULL);

#endif

}

/*

NETSCAPE2.0

  http://odur.let.rug.nl/~kleiweg/gif/netscape.html

  http://www.vurdalakov.net/misc/gif/netscape-looping-application-extension

  http://www.vurdalakov.net/misc/gif/netscape-buffering-application-extension

  https://code.google.com/p/gifdotnet/source/browse/src/GifDotNet/GifApplicationExtensionBlock.cs#95

  http://trac.webkit.org/browser/trunk/Source/WebCore/platform/image-decoders/gif/GIFImageReader.cpp#L617

ANIMEXTS1.0

  http://www.vurdalakov.net/misc/gif/animexts-looping-application-extension

  https://code.google.com/p/gifdotnet/source/browse/src/GifDotNet/GifApplicationExtensionBlock.cs#95

ICCRGBG1012

  http://www.color.org/icc1V42.pdf

XMP DataXMP

  http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart3.pdf

fractint

  http://fractint.net/fractsvn/trunk/fractint/common/loadfile.c

ZGATEXTI5 ZGATILEI5 ZGACTRLI5 ZGANPIMGI5

ZGAVECTI5 ZGAALPHAI5 ZGATITLE4.0 ZGATEXTI4.0

  Zoner GIF animator 4.0 and 5.0

*/

static const unsigned char *

gif_read_ae(fz_context *ctx, struct info *info, const unsigned char *p, const unsigned char *end)

{

  static char *ignorable[] = {

    "NETSACPE2.0", "ANIMEXTS1.0", "XMP DataXMP",

    "ZGATEXTI5\0\0", "ZGATILEI5\0\0", "ZGANPIMGI5\0", "ZGACTRLI5\0\0",

    "ZGAVECTI5\0\0", "ZGAALPHAI5\0", "ZGATITLE4.0", "ZGATEXTI4.0",

  };

  int i, ignored;

  if (end - p < 14)

    fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in application extension in gif image");

  if (p[2] != 0x0b)

    fz_throw(ctx, FZ_ERROR_FORMAT, "out of range application extension block size in gif image");

  ignored = 0;

  for (i = 0; i < (int)nelem(ignorable); i++)

    ignored |= memcmp(&p[3], ignorable[i], 8 + 3);

  if (!ignored)

  {

    char extension[9];

    memmove(extension, &p[3], 8);

    extension[8] = '\0';

    fz_warn(ctx, "ignoring unsupported application extension '%s' in gif image", extension);

  }

  if (!memcmp(&p[3], "ICCRGBG1012", 11))

    return gif_read_icc(ctx, info, p + 14, end);

  return gif_read_subblocks(ctx, info, p + 14, end, NULL);

}

static void

gif_mask_transparency(fz_context *ctx, struct info *info)

{

  unsigned char *mp = info->mask;

  unsigned char *dp = fz_pixmap_samples(ctx, info->pix);

  unsigned int x, y;

  for (y = 0; y < info->height; y++)

    for (x = 0; x < info->width; x++, mp++, dp += 4)

      if (*mp == 0x00)

        dp[3] = 0;

}

static fz_pixmap *

gif_read_image(fz_context *ctx, struct info *info, const unsigned char *p, size_t total, int only_metadata)

{

  const unsigned char *end = p + total;

  memset(info, 0x00, sizeof (*info));

  /* Read header */

  p = gif_read_header(ctx, info, p, end);

  /* Read logical screen descriptor */

  p = gif_read_lsd(ctx, info, p, end);

  if (only_metadata)

    return NULL;

  info->pix = fz_new_pixmap(ctx, fz_device_rgb(ctx), info->width, info->height, NULL, 1);

  fz_try(ctx)

  {

    info->mask = fz_calloc(ctx, (size_t)info->width * info->height, 1);

    /* Read optional global color table */

    if (info->has_gct)

    {

      unsigned char *bp, *dp = fz_pixmap_samples(ctx, info->pix);

      unsigned int x, y, k;

      p = gif_read_gct(ctx, info, p, end);

      bp = &info->gct[info->gct_background * 3];

      memset(info->mask, 0x01, (size_t)info->width * info->height);

      for (y = 0; y < info->height; y++)

        for (x = 0; x < info->width; x++, dp += 4)

        {

          for (k = 0; k < 3; k++)

            dp[k] = bp[k];

          dp[3] = 255;

        }

    }

    while (1)

    {

      /* Read block indicator */

      if (end - p < 1)

        fz_throw(ctx, FZ_ERROR_FORMAT, "premature end of block indicator in gif image");

      /* Read trailer */

      if (p[0] == 0x3b)

      {

        break;

      }

      /* Read extension */

      else if (p[0] == 0x21)

      {

        /* Read extension label */

        if (end - p < 2)

          fz_throw(ctx, FZ_ERROR_FORMAT, "premature end in extension label in gif image");

        if (p[1] == 0x01 && info->gif89a)

        {

          /* Read plain text extension */

          p = gif_read_pte(ctx, info, p, end);

          /* Graphic control extension applies only to the graphic rendering block following it */

          info->transparent = 0;

          info->has_transparency = 0;

        }

        else if (p[1] == 0xf9 && info->gif89a)

          /* Read graphic control extension */

          p = gif_read_gce(ctx, info, p, end);

        else if (p[1] == 0xfe && info->gif89a)

          /* Read comment extension */

          p = gif_read_ce(ctx, info, p, end);

        else if (p[1] == 0xff && info->gif89a)

          /* Read application extension */

          p = gif_read_ae(ctx, info, p, end);

        else

        {

          fz_warn(ctx, "ignoring unsupported extension label %02x in gif image", p[1]);

          p = gif_read_subblocks(ctx, info, p + 2, end, NULL);

        }

      }

      /* Read image descriptor */

      else if (p[0] == 0x2c)

      {

        p = gif_read_id(ctx, info, p, end);

        if (info->has_lct)

          /* Read local color table */

          p = gif_read_lct(ctx, info, p, end);

        /* Read table based image data */

        p = gif_read_tbid(ctx, info, p, end);

        /* Graphic control extension applies only to the graphic rendering block following it */

        info->transparent = 0;

        info->has_transparency = 0;

        /* Image descriptor applies only to the table based image data following it */

        info->image_left = info->image_top = 0;

        info->image_width = info->width;

        info->image_height = info->height;

        info->image_interlaced = 0;

        fz_free(ctx, info->lct);

        info->lct = NULL;

        info->has_lct = 0;

      }

      else

        fz_throw(ctx, FZ_ERROR_FORMAT, "unsupported block indicator %02x in gif image", p[0]);

    }

    gif_mask_transparency(ctx, info);

    fz_premultiply_pixmap(ctx, info->pix);

  }

  fz_always(ctx)

  {

    fz_free(ctx, info->mask);

    fz_free(ctx, info->lct);

    fz_free(ctx, info->gct);

  }

  fz_catch(ctx)

  {

    fz_drop_pixmap(ctx, info->pix);

    fz_rethrow(ctx);

  }

  return info->pix;

}

fz_pixmap *

fz_load_gif(fz_context *ctx, const unsigned char *p, size_t total)

{

  fz_pixmap *image;

  struct info gif;

  image = gif_read_image(ctx, &gif, p, total, 0);

  image->xres = gif.xres;

  image->yres = gif.yres;

  return image;

}

void

fz_load_gif_info(fz_context *ctx, const unsigned char *p, size_t total, int *wp, int *hp, int *xresp, int *yresp, fz_colorspace **cspacep)

{

  struct info gif;

  gif_read_image(ctx, &gif, p, total, 1);

  *cspacep = fz_keep_colorspace(ctx, fz_device_rgb(ctx));

  *wp = gif.width;

  *hp = gif.height;

  *xresp = gif.xres;

  *yresp = gif.yres;

}