Re: Simple string conversion from UCS2 to ISO8859-1

On Fri, 21 Feb 2025 12:40:06 +0100, pozz <pozzugno@gmail.com> wrote:

I want to write a simple function that converts UCS2 string into ISO8859-1:
>
void ucs2_to_iso8859p1(char *ucs2, size_t size);
>
ucs2 is a string of type "00480065006C006C006F" for "Hello". I'm passing
size because ucs2 isn't null terminated.
>
I know I can use iconv() feature, but I'm on an embedded platform
without an OS and without iconv() function.
>
It is trivial to convert "0000"-"007F" chars: it's a simple cast from
unsigned int to char.
>
It isn't so simple to convert higher codes. For example, the small e
with grave "00E8" can be converted to 0xE8 in ISO8859-1, so it's trivial
again. But I saw the code "2019" (apostrophe) that can be rendered as
0x27 in ISO8859-1.
>
Is there a simplified mapping table that can be written with if/switch?
>
if (code < 0x80) {
  *dst++ = (char)code;
} else {
  switch (code) {
    case 0x2019: *dst++ = 0x27; break;  // Apostrophe
    case 0x...: *dst++ = ...; break;
    default: *ds++ = ' ';
  }
}
>
I'm not searching a very detailed and correct mapping, but just a
"sufficient" implementation.
>

#include <stdint.h>
#include <stddef.h>

// Function to convert UCS2 to ISO8859-1
void UCS2ToISO88591(const uint16_t* ucs2, size_t length, char* iso88591) {
    for (size_t i = 0; i < length; ++i) {
        uint16_t ucs2_char = ucs2[i];
        if (ucs2_char <= 0x00FF) {
            iso88591[i] = (char)ucs2_char;
        } else {
            // Handle characters that cannot be represented in ISO8859-1
            iso88591[i] = '?'; // Replace with a placeholder character
        }
    }
    // Null-terminate the ISO8859-1 string
    iso88591[length] = '\0';
}