Hi All!

Current lib/gui/picopng.c has problems on big-endian CPUs.

Here are two examples from PNG_readPngHeader():

        if (*(uint64_t *) in != PNG_SIGNATURE) {
...
        if (*(uint32_t *) &in[12] != CHUNK_IHDR) {


Using memcmp in this situation is much better, e.g.

+       uint8_t png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
...
+       if (memcmp(in, png_signature, 8)) {


+       uint8_t chunk_header[4] = {0x49, 0x48, 0x44, 0x52};
...
+       if (memcmp(&in[12], chunk_header, 4)) {


Current lodepng works fine on big-endian, but can we disable picopng
in Kconfig for big-endian CPUs?

On mips I have CPU_BIG_ENDIAN option, so I can add
'depends on !CPU_BIG_ENDIAN' to lib/gui/Kconfig, e.g.

 config PICOPNG
+       depends on !CPU_BIG_ENDIAN
        bool "picoPNG"

-- 
Best regards,
  Antony Pavlov

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