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C++: Is it possible to condense `bool` objects within the same byte?


C++: Is it possible to condense `bool` objects within the same byte?

By : Clark Gibson
Date : November 17 2020, 04:01 AM
will help you You can use bitfields. Works with Repl.it's gcc version 4.6.3.
code :
#include <iostream>

struct Test 
{
  bool a:1;
  bool b:1;
  bool c:1;
  bool d:1;
  bool e:1;
  bool f:1;
  bool g:1;
  bool h:1;
  //bool i:1; //would increase size to 2 bytes.
};

int main()
{
  Test t;
  std::cout << sizeof(t) << std::endl;
  return 0;
}


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Extract the low bit of each bool byte in a __m128i? bool array to packed bitmap

Extract the low bit of each bool byte in a __m128i? bool array to packed bitmap


By : user7911342
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further So your source data is contiguous? You should use _mm_load_si128 instead of messing around with scalar components of vector types.
code :
#include <immintrin.h>
#include <stdint.h>

// n is the number of uint16_t dst elements
// We access n*16 bool elements from src.
void pack_bools(uint16_t *dst, const bool *src, size_t n)
{
     // you can later access dst with __m128i loads/stores

    __m128i carry_to_highbit = _mm_set1_epi8(0x7F);
    for (size_t i = 0 ; i < n ; i+=1) {
        __m128i boolvec = _mm_loadu_si128( (__m128i*)&src[i*16] );
        __m128i highbits = _mm_add_epi8(boolvec, carry_to_highbit);
        dst[i] = _mm_movemask_epi8(highbits);
    }
}
.L3:
    movdqu  xmm0, XMMWORD PTR [rsi]
    add     rsi, 16
    add     rdi, 2
    paddb   xmm0, xmm1
    pmovmskb        eax, xmm0
    mov     WORD PTR [rdi-2], ax
    cmp     rdx, rsi
    jne     .L3
Condense a list of objects if a property on the object is the same

Condense a list of objects if a property on the object is the same


By : bob
Date : March 29 2020, 07:55 AM
Hope this helps I have a list of objects that look like this: , You can indeed make this more concise.
code :
List<MyObject> condense(List<MyObject> fullList) {
      Map<String, MyObject> tempMap = new HashMap<>();
      fullList.forEach(a -> tempMap.merge(a.getId(), a, MyObject::merge));
      return new ArrayList<>(tempMap.values());
}
Flatbuffers: table bool value set with byte instead of bool

Flatbuffers: table bool value set with byte instead of bool


By : Omar Saadoun
Date : March 29 2020, 07:55 AM
it fixes the issue Booleans are certainly stored as a byte in the FlatBuffers binary format, but there is no reason it can't convert it to boolean upon access, as happens in other languages.
So this may well be a bug in Go code generator, I'd file an issue on github, tagged by [Go].
What is a efficient way to condense a List of objects to based on an object value?

What is a efficient way to condense a List of objects to based on an object value?


By : Nicholas K Koskie
Date : March 29 2020, 07:55 AM
will help you You can define a Map where the key is the name and value is the object instance.
Go through the list and for each instance check whether it exists in the map.
[]byte to []int or []bool

[]byte to []int or []bool


By : nix1138
Date : March 29 2020, 07:55 AM
this will help There is no ready function in the standard lib that would do that. Here's a possible solution using a loop:
code :
func convert(data []byte) []bool {
    res := make([]bool, len(data)*8)
    for i := range res {
        res[i] = data[i/8]&(0x80>>byte(i&0x7)) != 0
    }
    return res
}
data := []byte{0x41, 0x01}
fmt.Println("intput bytes:", data)

bi := big.NewInt(0)
bi.SetBytes(data)
fmt.Println("data:", bi.Text(2))

fmt.Println("7. bit before:", bi.Bit(7))
bi.SetBit(bi, 7, 1)
fmt.Println("7. bit after:", bi.Bit(7))
fmt.Println("data:", bi.Text(2))
fmt.Println("output bytes:", bi.Bytes())
intput bytes: [65 1]
data: 100000100000001
7. bit before: 0
7. bit after: 1
data: 100000110000001
output bytes: [65 129]
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