#pragma once vs. #ifndef

#pragma once is NOT standard
But #ifndef is standard
#ifndef XXX_YYYY
#define XXX_YYYY


#endif // XXX_YYYY

In the compile-time #pragma once is faster.

https://stackoverflow.com/questions/1143936/pragma-once-vs-include-guards
https://beesbuzz.biz/code/1473-pragma-once-vs-ifndef-define

[VS Code] enable define in C & C++

Setting Visual Studio Code

c_cpp_properties.json
ctrl+shift+p
>C/C++:Edit Configuration (JSON)

Make c_cpp_properties.json in .vscode folder, and
 - Updated c_cpp_properties.json syntax

"configurations": [
    {
        "defines": [
            "WIN32",
        ],
        // ...
    }
],

AVX2 vs. AVX512

https://stackoverflow.com/questions/52523349/avx-512-vs-avx2-performance-for-simple-array-processing-loops

Daniel Lemire's blog
 - AVX-512: when and how to use these new instructions
 - The dangers of AVX-512 throttling: myth or reality?

How can I find what instruction set extension is supported in my Intel Processor?

https://www.intel.com/content/www/us/en/support/articles/000005779/processors.html

1. Go to https://ark.intel.com/content/www/us/en/ark.html site
2. Processors
3. Select Intel xxx Processor type
4. Select Product Name: Intel® Core™ i7-5500U Processor
5. Find "Advanced Technology"
You can find the supported SIMD instructions
 Intel i7-5500U can support: Intel® SSE4.1, Intel® SSE4.2, Intel® AVX2

And 
How to Identify My Intel® Processor
And gcc x86 options
https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html

How to add commend in "macro function" or #define ?

int small_func(int a)
{
    // input plus two
    return (a + 2);
}

#define SMALL_FUNC(a) ({ \
    int result;
    do { \
        /* input plus two */ \
        result = a + 2; \
    } while(0); \
    result; \
})

How to Add Comments to Macros

for loop multiple conditions

what is the right?
1. for (i = 0, j = 0; i < loop, j < loop2; i++, j++)
2. for (i = 0, j = 0; (i < loop) && (j < loop2); i++, j++)

The answers are
Are multiple conditions allowed in a for loop?
GeeksforGeeks: Output of C Program | Set 22, question 2

for example
i = 1, 2; is same as i = 2;

TI DSP memory & memory map

L2SRAM: very very fast
MSMCSRAM (Multi-core Shared Memory Controller, SRAM): very fast
DDR3: fast

TI Linker Command File Primer