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From 127b08a265f99ce517ea31ec7988a91fc17da4d9 Mon Sep 17 00:00:00 2001
From: Glenn Randers-Pehrson <glennrp at users.sourceforge.net>
Date: Sun, 5 May 2013 22:13:47 -0500
Subject: [PATCH 09/10] [libpng16] Calculate our own zlib windowBits when
decoding rather than
trusting the CMF bytes in the PNG datastream.
---
ANNOUNCE | 6 +++--
CHANGES | 5 +++-
pngrutil.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
3 files changed, 88 insertions(+), 10 deletions(-)
(foutrelis: pruned non-code changes to apply cleanly to libpng 1.6.2.)
diff --git a/pngrutil.c b/pngrutil.c
index 01c3679..9c10e26 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -18,8 +18,6 @@
#ifdef PNG_READ_SUPPORTED
-#define png_strtod(p,a,b) strtod(a,b)
-
png_uint_32 PNGAPI
png_get_uint_31(png_const_structrp png_ptr, png_const_bytep buf)
{
@@ -4165,6 +4163,75 @@ png_read_finish_row(png_structrp png_ptr)
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_READ_OPTIMIZE_WINDOWBITS_SUPPORTED
+/* This is the code to to select a windowBits value to match the smallest
+ * possible sliding window needed to contain the entire uncompressed image.
+ */
+static unsigned int
+required_window_bits(png_alloc_size_t data_size)
+{
+ unsigned int windowBits = 15;
+ if (data_size <= 16384) /* else windowBits must be 15 */
+ {
+ unsigned int half_z_window_size = 1U << (windowBits-1); /* 16384 */
+
+ do
+ {
+ half_z_window_size >>= 1;
+ --windowBits;
+ }
+ while (windowBits > 8 && data_size <= half_z_window_size);
+ }
+ return windowBits;
+}
+/* This is used below to find the size of an image to pass to png_deflate_claim,
+ * so it only needs to be accurate if the size is less than 16384 bytes (the
+ * point at which a lower LZ window size can be used.)
+ *
+ * To do: merge this with png_image_size() in pngwutil.c and put the result
+ * in png.c as a PNG_INTERNAL_FUNCTION.
+ */
+static png_alloc_size_t
+png_read_image_size(png_structrp png_ptr)
+{
+ /* Only return sizes up to the maximum of a png_uint_32, do this by limiting
+ * the width and height used to 15 bits.
+ */
+ png_uint_32 h = png_ptr->height;
+
+ if (png_ptr->rowbytes < 32768 && h < 32768)
+ {
+ if (png_ptr->interlaced)
+ {
+ /* Interlacing makes the image larger because of the replication of
+ * both the filter byte and the padding to a byte boundary.
+ */
+ png_uint_32 w = png_ptr->width;
+ unsigned int pd = png_ptr->pixel_depth;
+ png_alloc_size_t cb_base;
+ int pass;
+
+ for (cb_base=0, pass=0; pass<=6; ++pass)
+ {
+ png_uint_32 pw = PNG_PASS_COLS(w, pass);
+
+ if (pw > 0)
+ cb_base += (PNG_ROWBYTES(pd, pw)+1) * PNG_PASS_ROWS(h, pass);
+ }
+
+ return cb_base;
+ }
+
+ else
+ return (png_ptr->rowbytes+1) * h;
+ }
+
+ else
+ return 0xffffffffU;
+}
+
+#endif /* PNG_READ_OPTIMIZE_WINDOWBITS_SUPPORTED */
+
void /* PRIVATE */
png_read_start_row(png_structrp png_ptr)
{
@@ -4449,14 +4516,20 @@ defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
png_free(png_ptr, buffer);
}
- /* Finally claim the zstream for the inflate of the IDAT data, use the bits
- * value from the stream (note that this will result in a fatal error if the
- * IDAT stream has a bogus deflate header window_bits value, but this should
- * not be happening any longer!)
+ /* Finally claim the zstream for the inflate of the IDAT data, using the
+ * windowBts predicted from the uncompressed data size, not the value from
+ * the stream. If READ_OPTIMIZE_WINDOWBITS_SUPPORTED is not defined, then
+ * simply use a 32kbyte window (windowBits=15).
*/
- if (png_inflate_claim(png_ptr, png_IDAT, 0) != Z_OK)
+#ifdef PNG_READ_OPTIMIZE_WINDOWBITS_SUPPORTED
+ if (png_inflate_claim(png_ptr, png_IDAT,
+ required_window_bits(png_read_image_size(png_ptr))) != Z_OK)
+#else
+ if (png_inflate_claim(png_ptr, png_IDAT, 15) != Z_OK)
+#endif
png_error(png_ptr, png_ptr->zstream.msg);
png_ptr->flags |= PNG_FLAG_ROW_INIT;
}
+
#endif /* PNG_READ_SUPPORTED */
--
1.8.2.2
|