Convet HEX-encoded UCS2 string to text with support of Ukrainian

To convert a HEX-encoded UCS2 string to text with support for the Ukrainian language, you'll need to decode the HEX representation, convert it to UTF-16, and then further convert it to UTF-8 encoding. The following C code demonstrates how to accomplish this: 

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


int hex_to_int(char ch) {
    if (ch >= '0' && ch <= '9') return ch - '0';
    if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10;
    if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10;
    return -1;
}

int hex_to_utf16(const char *hex, uint16_t *utf16) {
    int len = strlen(hex);
    if (len % 4 != 0) return -1;

    for (int i = 0; i < len; i += 4) {
        int high_byte = (hex_to_int(hex[i]) << 4) + hex_to_int(hex[i + 1]);
        int low_byte = (hex_to_int(hex[i + 2]) << 4) + hex_to_int(hex[i + 3]);
        utf16[i / 4] = (high_byte << 8) | low_byte;
    }

    return len / 4;
}

int utf16_to_utf8(const uint16_t *utf16, int utf16_len, char *utf8) {
    int utf8_len = 0;
    for (int i = 0; i < utf16_len; i++) {
        uint16_t codepoint = utf16[i];

        if (codepoint <= 0x7F) {
            utf8[utf8_len++] = codepoint;
        } else if (codepoint <= 0x7FF) {
            utf8[utf8_len++] = 0xC0 | (codepoint >> 6);
            utf8[utf8_len++] = 0x80 | (codepoint & 0x3F);
        } else {
            utf8[utf8_len++] = 0xE0 | (codepoint >> 12);
            utf8[utf8_len++] = 0x80 | ((codepoint >> 6) & 0x3F);
            utf8[utf8_len++] = 0x80 | (codepoint & 0x3F);
        }
    }
    utf8[utf8_len] = '\0';
    return utf8_len;
}

int main() {
    const char *hex_encoded_ucs2 = "041F04400438043B0438043D0430";
    uint16_t utf16[strlen(hex_encoded_ucs2) / 4];

    int utf16_len = hex_to_utf16(hex_encoded_ucs2, utf16);
    if (utf16_len < 0) {
        fprintf(stderr, "Invalid HEX-encoded UCS2 string\n");
        return 1;
    }

    char utf8[utf16_len * 4];
    int utf8_len = utf16_to_utf8(utf16, utf16_len, utf8);
    if (utf8_len < 0) {
        fprintf(stderr, "Error converting UTF-16 to UTF-8\n");
        return 1;
    }

    printf("Converted text: %s\n", utf8);
    return 0;
}

What is UCS-2?

UCS-2 (Universal Character Set 2) is an early character encoding standard that uses a fixed-size 16-bit (2-byte) representation for each character. It was introduced in 1993 as a part of the Unicode standard, with the goal of providing a consistent way of encoding a wide range of characters from different writing systems. UCS-2 can represent a total of 65,536 unique characters, which was initially believed to be sufficient to cover most of the world's writing systems. However, it soon became clear that this was not enough to cover all characters, particularly with the inclusion of historic scripts, symbols, and additional characters from various languages. As a result, UCS-2 was effectively replaced by UTF-16 (Unicode Transformation Format 16-bit), which uses variable-length encoding (either 2 or 4 bytes) to represent a much larger range of characters. UTF-16 can represent over a million unique characters, providing better support for various writing systems, including those that require a large number of characters. While UCS-2 and UTF-16 are similar in many ways, there are some important differences. The main difference is that UCS-2 uses a fixed 2-byte representation for each character, whereas UTF-16 can use either 2 or 4 bytes, depending on the character being encoded. This means that UCS-2 is limited to the Basic Multilingual Plane (BMP), which includes the first 65,536 Unicode characters, while UTF-16 can represent characters from all Unicode planes.