I have this function to fill a buffer with a repeating pattern of N bytes.

void* memsetPattern(void* buf, size_t bufSize, const void* Pattern, size_t PatternSize) {
    if (buf == nullptr || Pattern == nullptr || PatternSize == 0) { return nullptr; }
    if (bufSize == 0) { return buf; } // 0 Bytes to copy
    if (PatternSize == 1) {
        memset(buf, ((uint8_t*)Pattern)[0], bufSize);
        return buf;
    }
    /* otherwise, if PatternSize >= 2 */
}

If the PatternSize is 1 byte, the function will instead run memset(buf, ((uint8_t*)Pattern)[0], bufSize), since memset runs slightly faster than my function.

If the user wanted to call memsetPattern(buf, bufSize, Pattern, 1), would it be possible to directly call (Pattern != nullptr && buf != nullptr) ? memset(buf, ((uint8_t*)Pattern)[0], bufSize) : nullptr since PatternSize would be known to equal 1 byte at compile time?

I suppose one way to do it is with Macros, but it just feels wrong.

#define memsetPattern_Macro(buf, bufSize, Pattern, PatternSize) 
(PatternSize == 1) ? ( 
    (Pattern != nullptr && buf != nullptr) ? memset(buf, ((uint8_t*)Pattern)[0], bufSize) : nullptr 
) : memsetPattern(buf, bufSize, Pattern, PatternSize)

Looking around, I did find if constexpr (), but it gives an error if I try if constexpr (PatternSize == 1) {.

How should I go about switching the function based on parameters that are known at compile time? Would I need to change the types of arguments that are passed into the memsetPattern() function?