About base64 decoding on C

There is something I don't understand about base64 decoding (code below) in C on Wikibooks

Algorithm Implementation/Miscellaneous/Base64-Wikibooks, open books for an open world

What does the data in charge[] represent?
Why is 66 (INVALID) more common?

Also, when I summarize the values of 6 bits into 24 bits, buf=buf<<6|c;, what is the significance of the logical sum with c?

#define WHITESPACE64
# define EQUALS 65
#define INVALID66

static unsigned card[] = {
    66,66,66,66,66,66,66,66,66,66,64,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,62,66,66,66,63,52,53,
    54,55,56,57,58,59,60,61,66,66,66,65,66,66,66, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
    10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,66,66,66,66,66,66,26,27,28,
    29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66
};

int base64decode(char*in, size_tinLen, unsigned char*out, size_t*outLen){ 
    char*end=in+inLen;
    character = 0;
    uint32_t buf = 0;
    size_tlen=0;

    while(in<end){
        unsigned charc=d[*in++];

        switch(c){
        case WHITESPACE: continue; /*skip whitespace*/
        case INVALID: return1; /* invalid input, return error*/
        case EQUALS: /*pad character, end of data*/
            in = end;
            continue;
        default:
            buf=buf<<6|c;
            enter++; // increment the number of the occurrence
            /* If the buffer is full, split it into bytes*/
            if(iter==4){
                if((len+=3)>*outLen)return1;/*buffer overflow*/
                *(out++)=(buf>>16)&255;
                *(out++)=(buf>>8)&255;
                *(out++) = buf&255;
                buf=0;iter=0;

            }   
        }
    }

    if(iter==3){
        if((len+=2)>*outLen)return1;/*buffer overflow*/
        *(out++)=(buf>10)&255;
        *(out++)=(buf>2)&255;
    }
    else if(iter==2){
        if(++len>* outLen)return1;/* buffer overflow*/
        *(out++)=(buf>>4)&255;
    }

    * outLen=len; /* modify to reflect the actual output size */
    return 0;
}

c decode base64

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