[Crash-utility] Re: [PATCH v4 ] Adding the zram decompression algorithm "lzo-rle" to support kernel versions >= 5.1

[lijiang <lijiang@xxxxxxxxxx>]

On Tue, Apr 16, 2024 at 4:01 PM HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab@xxxxxxx> wrote:

On 2024/04/16 15:49, Yulong Tang wrote:
>> On Mon, Apr 15, 2024 at 2:32 PM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab(a)nec.com&gt;
>> wrote:
>>
>>
>> Sure. The macro '#if __BYTE_ORDER == __BIG_ENDIAN' takes effect on a
>> big-endian machine. But it requires to include the header file 'byteswap.h'
>> as below:
>> #include <byteswap.h>
>>
>> In addition, there is a similar implementation, but I haven't tested it
>> with Yulong's case. Can you help to check if this can work well for you?
>> Yulong.
>>
>> static inline uint16_t
>> get_unaligned_le16 (const uint8_t *p)
>> {
>>    return p[0] | p[1] << 8;
>> }

Ah nice, this looks simple and better.  If it works well on a big-endian
machine too, let's go with this.

I tested these two functions with a test case, for example:

unsigned int x = 0x76543210;

big-endian machine:
call get_unaligned_le16_v1(): 0x5476

call get_unaligned_le16_v2(): 0x5476

little-endian machine:
call get_unaligned_le16_v1(): 0x3210

call get_unaligned_le16_v2(): 0x3210

---------------------------code---------------------------------------

static uint16_t get_unaligned_le16_v1(const void *p) {
uint16_t value;
memcpy(&value, p, sizeof(uint16_t));
   #if __BYTE_ORDER == __BIG_ENDIAN
       return bswap_16(value);
   #else
       return value;
   #endif
}

static inline uint16_t
get_unaligned_le16_v2(const uint8_t *p)
{
  return p[0] | p[1] << 8;
}

---------------------------code---------------------------------------

They have the same results on the little-endian/big-endian machine from my side.

>>
>
> Hi, Lianbo
>
> It works well in my case(little-endian). This looks promising, but I don't have a big-

Thank you for the confirmation, Yulong.

 

Thanks

Lianbo

endian machine to test it on.

Thank you for testing, Yulong.

Thanks,
Kazu

--
Crash-utility mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxxxxxx
https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/
Contribution Guidelines: https://github.com/crash-utility/crash/wiki