picopng does not support big-endian CPUs

picopng does not support big-endian CPUs

[Antony Pavlov]

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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Re: 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

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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Re: picopng does not support big-endian CPUs

[Jean-Christophe PLAGNIOL-VILLARD]

> On Jan 26, 2015, at 3:58 PM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> 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.
> 


IIRC the code this can be fixed easy as I run this code on a mac G5 in the past

I’ll take a if I still have the code

Best Regards,
J.
> Sascha
> 
> -- 
> Pengutronix e.K.                           |                             |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |


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