#C - Display Hexidecimal as Little Endian instead of Big Endian

31 messages · Page 1 of 1 (latest)

untold field
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I for the life of me cannot figure out how to output hexidecimal as little endian, I know there's a way to do it without rewriting the book of life.

I don't really want someone to solve it for me, just help me jog my memory a bit, it's gotta be simple.

📎 PPIT_XYR.c
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#

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untold field
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Please ignore the brute force use of unions, it's just a temporary utility.

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I have to flip the results manually, don't I? 😐

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untold field
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My attempt at rewriting this failed, so re-asking the question so hopefully someone else knows the answer.

jagged flame
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What is PRIx32?

verbal mural
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maybe you could convert the number to little endian before printing it?

untold field
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PRIX32 is a lowercase hexadecimal printf format for uint32_t

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That's the thing, I'm trying to figure out how, is there a way print it out in little endian

verbal mural
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I mean just printing out the integer converted to little endian, for example with htole32()

#

just flip the numbers endianess

calm oyster
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@untold field Could you give a sample input and output?

untold field
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Input: 30 40 90
Output:
''X Coord : 30.000000 is 0x41f00000
Y Coord : 40.000000 is 0x42200000
Rotation : 90.000000 is 0x42b40000''
Wanted Output:
''X Coord : 30.000000 is 0x0000f041
Y Coord : 40.000000 is 0x00002042
Rotation : 90.000000 is 0x0000b442''

untold field
verbal mural
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it just needs to be the opposite of the host endian

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though I just realized that it converts leading zeros to trailing zeroes

calm oyster
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@untold field Do you know an algorithm for adding up the digits of a number?

untold field
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Oh my god, digit summing, I was hoping for something akin to htobe32(), but I'm afraid I'm in a Windows DE, which means I can't use endian.h.

calm oyster
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Will you answer my question?

untold field
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Afraid I do not.

calm oyster
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unsigned change_endianness(unsigned x)
{
    unsigned y = 0;
    
    while (x != 0)
    {
        y = (y << 8) + x % 256U;
        x = x / 256U;
    }
    
    return y;
}
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Here's an idea.

untold field
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Wow. that's more than an idea.

calm oyster
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unsigned change_endianness(unsigned x)
{
    unsigned y = 0;
    
    for (int i = 0; i < sizeof x; ++i)
    {
        y = (y << 8) + x % 256;
        x = x / 256;
    }
    
    return y;
}
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@untold field This implementation is better.

untold field
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Much appreciated!

jagged flame
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You could also use smth like

union int_bytes {
  uint32_t val;
  uint8_t bytes[sizeof(uint32_t)];
}

Then construct a union from the passed x and iterate from the last to first array element, which are the individual bytes from least significant to most significant, and print them.

#

Could even do something like:

union int_bytes {
  uint32_t val;
  struct {
    uint8_t most_significant;
    uint8_t second_most_significant;
    uint8_t second_least_significant;
    uint8_t least_significant;
  }
}