picopng does not support big-endian CPUs

[Sascha Hauer]

On Sun, Jan 25, 2015 at 10:26:29PM +0400, Antony Pavlov wrote:
> 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?

Can't we just fix it? Are there more difficult places than the ones
above? If it turns out to be difficult I'm fine with adding a dependency
to CPU_BIG_ENDIAN.

Sascha

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