perf: jpeg2000 valid_file implementation, much faster than trying to open (#4548)

Primary cost of detecting whether a given file is valid jpeg2000 file is
the thread pool initialization and shutdown that `Jpeg2000Input::open`
does (the actual thread pool part is inside OpenJpeg code).

So add a dedicated `valid_file()` implementation that only needs to
check 12 bytes of the header. While at it, I changed already existing
`isJp2File()` to `is_jp2_header()` to better match naming conventions
used elsewhere, and instead of trying to handle both little and big
endian cases by manual repetition of two sets of magic integers, let's
do just byte comparisons with `memcmp` instead.

On my PC (Ryzen 5950X, SSD, Windows VS2022), doing
`ImageInput::create()` on 1138 files where they are not images at all
(so OIIO in turns tries all the input plugins on them):

- Before: **3.4 seconds** spent in `Jpeg2000Input::open` (1.9s
`opj_thread_pool_create`, 1.3s `opj_thread_pool_destroy`)
- After: **33 milliseconds** spent in `Jpeg2000Input::valid_file`

No new tests. I checked behavior on the official Jpeg2000 conformance
data set
(https://github.com/uclouvain/openjpeg-data/tree/master/input/conformance),
seems to work.


Signed-off-by: Aras Pranckevicius <[email protected]>

Author: aras-p

src/jpeg2000.imageio/jpeg2000input.cpp

@@ -80,6 +80,7 @@ class Jpeg2000Input final : public ImageInput {
         return feature == "ioproxy";
         // FIXME: we should support Exif/IPTC, but currently don't.
     }
+    bool valid_file(Filesystem::IOProxy* ioproxy) const override;
     bool open(const std::string& name, ImageSpec& spec) override;
     bool open(const std::string& name, ImageSpec& newspec,
               const ImageSpec& config) override;
@@ -97,7 +98,8 @@ class Jpeg2000Input final : public ImageInput {
 
     void init(void);
 
-    bool isJp2File(const int* const p_magicTable) const;
+    static bool is_jp2_header(const uint8_t header[12]);
+    static bool is_j2k_header(const uint8_t header[5]);
 
     opj_codec_t* create_decompressor();
     void destroy_decompressor();
@@ -208,7 +210,19 @@ Jpeg2000Input::init(void)
     ioproxy_clear();
 }
 
+bool
+Jpeg2000Input::valid_file(Filesystem::IOProxy* ioproxy) const
+{
+    if (!ioproxy || ioproxy->mode() != Filesystem::IOProxy::Mode::Read)
+        return false;
 
+    uint8_t header[12];
+    auto r = ioproxy->pread(header, sizeof(header), 0);
+    if (r != sizeof(header)) {
+        return false;
+    }
+    return is_jp2_header(header) || is_j2k_header(header);
+}
 
 bool
 Jpeg2000Input::open(const std::string& name, ImageSpec& p_spec)
@@ -409,36 +423,32 @@ Jpeg2000Input::close(void)
     return true;
 }
 
-
 bool
-Jpeg2000Input::isJp2File(const int* const p_magicTable) const
+Jpeg2000Input::is_jp2_header(const uint8_t header[12])
 {
-    const int32_t JP2_MAGIC = 0x0000000C, JP2_MAGIC2 = 0x0C000000;
-    if (p_magicTable[0] == JP2_MAGIC || p_magicTable[0] == JP2_MAGIC2) {
-        const int32_t JP2_SIG1_MAGIC = 0x6A502020, JP2_SIG1_MAGIC2 = 0x2020506A;
-        const int32_t JP2_SIG2_MAGIC = 0x0D0A870A, JP2_SIG2_MAGIC2 = 0x0A870A0D;
-        if ((p_magicTable[1] == JP2_SIG1_MAGIC
-             || p_magicTable[1] == JP2_SIG1_MAGIC2)
-            && (p_magicTable[2] == JP2_SIG2_MAGIC
-                || p_magicTable[2] == JP2_SIG2_MAGIC2)) {
-            return true;
-        }
-    }
-    return false;
+    const uint8_t jp2_header[] = { 0x0,  0x0,  0x0,  0x0C, 0x6A, 0x50,
+                                   0x20, 0x20, 0x0D, 0x0A, 0x87, 0x0A };
+    return memcmp(header, jp2_header, sizeof(jp2_header)) == 0;
 }
 
+bool
+Jpeg2000Input::is_j2k_header(const uint8_t header[5])
+{
+    const uint8_t j2k_header[] = { 0xFF, 0x4F, 0xFF, 0x51, 0x00 };
+    return memcmp(header, j2k_header, sizeof(j2k_header)) == 0;
+}
 
 opj_codec_t*
 Jpeg2000Input::create_decompressor()
 {
-    int magic[3];
-    auto r = ioproxy()->pread(magic, sizeof(magic), 0);
-    if (r != 3 * sizeof(int)) {
+    uint8_t header[12];
+    auto r = ioproxy()->pread(header, sizeof(header), 0);
+    if (r != sizeof(header)) {
         errorfmt("Empty file \"{}\"", m_filename);
         return nullptr;
     }
-    return opj_create_decompress(isJp2File(magic) ? OPJ_CODEC_JP2
-                                                  : OPJ_CODEC_J2K);
+    return opj_create_decompress(is_jp2_header(header) ? OPJ_CODEC_JP2
+                                                       : OPJ_CODEC_J2K);
 }