CODEWITHSUNDEEP
cc-preprocessor
JDC
JDC

Reputation: 43

Advance way to search for define in c

/* UART HEADER */
#define featureA        0xA0
#define featureB        0xB0
#define featureC        0x20
        -
        -
        -
        - // increment on feature, value of feature are random
        -
        -
#define featureZ     0x??

#define CHECK_CHAR(x) ((x==featureA)||(x==featureB)||(x==featureC) ------- (x==featureZ)? TRUE: FALSE)

Hi all, I got a set of UART header that to indicate what the commands for. So every time I am checking the header using the macro, but I realize that when the command is keep increasing and the macro length also keep increasing, it make the code very messy. I am looking for a mechanism to handle this checking when the feature is more and more.

Upvotes: 0

Views: 92

Answers (2)

Lundin
Lundin

Reputation: 213711

Since this seems to be a run-time check, you can speed up the program considerably by using a look-up table instead. It will also make the code more readable. Assuming you can spare 256 bytes of flash and all codes are unique, then:

bool CHECK_CHAR (uint8_t ch)
{
  const bool LOOKUP [256] = 
  {
    [featureA] = true,
    [featureB] = true,
    [featureC] = true,
  };

  return LOOKUP[ch];
}

The second best option is a sorted array of uint8_t constants + binary search.

Upvotes: 1

Daniel Walker
Daniel Walker

Reputation: 6740

Assuming that your values follow the simple pattern above, this would work:

#define CHECK_CHAR(x) ( ((x)&0xf) == 0 && (x) >= featureA && (x) < featureInvalid )

where you define featureInvalid to be the next logical value after featureZ.

Upvotes: 0

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