search for mem with hex pattern contains wildcards

mem_scan.c

#include <stdio.h>
#include <stdlib.h>

static void* mem_scan(const void* addr, size_t size, const char* hex_pattern) {
    union pattern_holder {
        struct {
            unsigned char content : 8;
            unsigned char mask : 8;
        };
        wchar_t pat_char;
    } pattern[1024] = { 0 };
    int pat_len = 0;
    const int pat_c_init = 0x1FF;
    int pat_c = pat_c_init;
    while(pat_len < 1024) {
        char c = *hex_pattern++;
        if (!c) {
            break;
        }
        switch (c) {
        case '\t':
        case '\n':
        case '\r':
        case ' ':
        case ',':
        case '-':
        case ':':
            continue;
        default:
            break;
        }

        unsigned char uc = (unsigned char)c;
        
        if (uc - '0' <= 9u) {
            pat_c = (pat_c << 4) | (uc - '0');
        } else if (uc - 'A' <= 6u) {
            pat_c = (pat_c << 4) | (uc - 'A' + 10);
        } else if (uc - 'a' <= 6u) {
            pat_c = (pat_c << 4) | (uc - 'a' + 10);
        } else if (c == '?') {
            pat_c = (pat_c ^ 0xF0) << 4;
        } else {
            return NULL;
        }
        if (pat_c & 0xFFFF0000) {
            pattern[pat_len++].pat_char = pat_c;
            pat_c = pat_c_init;
        }
    }
    if (!pat_len) return NULL;
    
    char* _addr = (char*)addr;
    for (int addr_off = 0; addr_off < size; addr_off++) {
        for (int pat_off = 0; pat_off <= pat_len; pat_off++) {
            if (pat_off == pat_len) {
                return _addr + addr_off;
            }
            if ((pattern[pat_off].mask & _addr[addr_off + pat_off]) != pattern[pat_off].content) {
                break;
            }
        }
    }
    return NULL;
}

int main() {
    char buf1[] = "ABCDEFGHIJKLMNOPQRST";
    char pat[] = "44 45 46 4? 48";
    //char pat[] = "41 4? 43";
    char *ret = (char *)mem_scan(buf1, sizeof(buf1), pat);
    printf("%d", ret - buf1);
}