/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/.

 *

 *    Copyright 2024 (c) Fraunhofer IOSB (Author: Julius Pfrommer)

 */

#include "utf8.h"

#define UTF_PARSE_BYTE(pos) do {                        \

        byte = str[pos];                                \

        if(UTF_UNLIKELY(byte < 0x80 || byte > 0xBF))    \

            return 0; /* Not a continuation byte */     \

        *codepoint = (*codepoint << 6) + (byte & 0x3F); \

    } while(0)

unsigned

utf8_to_codepoint(const unsigned char *str, size_t len, unsigned *codepoint) {

    /* Ensure there is a character to read */

    if(UTF_UNLIKELY(len == 0))

        return 0;

    *codepoint = str[0];

    if(UTF_LIKELY(*codepoint < 0x80))

        return 1; /* Normal ASCII */

    if(UTF_UNLIKELY(*codepoint <= 0xC1))

        return 0; /* Continuation byte not allowed here */

    unsigned count;

    unsigned char byte;

    if(*codepoint <= 0xDF) { /* 2-byte sequence */

        if(len < 2)

            return 0;

        count = 2;

        *codepoint &= 0x1F;

        UTF_PARSE_BYTE(1);

        if(UTF_UNLIKELY(*codepoint < 0x80))

            return 0; /* Too small for the encoding length */

    } else if(*codepoint <= 0xEF) { /* 3-byte sequence */

        if(len < 3)

            return 0;

        count = 3;

        *codepoint &= 0xF;

        UTF_PARSE_BYTE(1);

        UTF_PARSE_BYTE(2);

        if(UTF_UNLIKELY(*codepoint < 0x800))

            return 0; /* Too small for the encoding length */

    } else if(*codepoint <= 0xF4) { /* 4-byte sequence */

        if(len < 4)

            return 0;

        count = 4;

        *codepoint &= 0x7;

        UTF_PARSE_BYTE(1);

        UTF_PARSE_BYTE(2);

        UTF_PARSE_BYTE(3);

        if(UTF_UNLIKELY(*codepoint < 0x10000))

            return 0; /* Too small for the encoding length */

    } else {

        return 0; /* Invalid utf8 encoding */

    }

    if(UTF_UNLIKELY(*codepoint > 0x10FFFF))

        return 0; /* Not in the Unicode range */

    return count;

}