Subversion Repositories HelenOS

#include <errno.h>

#include <string.h>

/** Byte mask consisting of lowest @n bits (out of 8) */

#define LO_MASK_8(n)  ((uint8_t) ((1 << (n)) - 1))

/** Byte mask consisting of lowest @n bits (out of 32) */

#define LO_MASK_32(n)  ((uint32_t) ((1 << (n)) - 1))

/** Byte mask consisting of highest @n bits (out of 8) */

#define HI_MASK_8(n)  (~LO_MASK_8(8 - (n)))

/** Number of data bits in a UTF-8 continuation byte */

#define CONT_BITS  6

/** Decode a single character from a string.

 *

 * Decode a single character from a string of size @a size. Decoding starts

 * at @a offset and this offset is moved to the beginning of the next

 * character. In case of decoding error, offset generally advances at least

 * by one. However, offset is never moved beyond size.

 *

 * @param str    String (not necessarily NULL-terminated).

 * @param offset Byte offset in string where to start decoding.

 * @param size   Size of the string (in bytes).

 *

 * @return Value of decoded character, U_SPECIAL on decoding error or

 *         NULL if attempt to decode beyond @a size.

 *

 */

wchar_t str_decode(const char *str, size_t *offset, size_t size)

{

    if (*offset + 1 > size)

        return 0;

    /* First byte read from string */

    uint8_t b0 = (uint8_t) str[(*offset)++];

    /* Determine code length */

    unsigned int b0_bits;  /* Data bits in first byte */

    unsigned int cbytes;   /* Number of continuation bytes */

    if ((b0 & 0x80) == 0) {

        /* 0xxxxxxx (Plain ASCII) */

        b0_bits = 7;

        cbytes = 0;

    } else if ((b0 & 0xe0) == 0xc0) {

        /* 110xxxxx 10xxxxxx */

        b0_bits = 5;

        cbytes = 1;

    } else if ((b0 & 0xf0) == 0xe0) {

        /* 1110xxxx 10xxxxxx 10xxxxxx */

        b0_bits = 4;

        cbytes = 2;

    } else if ((b0 & 0xf8) == 0xf0) {

        /* 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx */

        b0_bits = 3;

        cbytes = 3;

    } else {

        /* 10xxxxxx -- unexpected continuation byte */

        return U_SPECIAL;

    }

    if (*offset + cbytes > size)

        return U_SPECIAL;

    wchar_t ch = b0 & LO_MASK_8(b0_bits);

    /* Decode continuation bytes */

    while (cbytes > 0) {

        uint8_t b = (uint8_t) str[(*offset)++];

        /* Must be 10xxxxxx */

        if ((b & 0xc0) != 0x80)

            return U_SPECIAL;

        /* Shift data bits to ch */

        ch = (ch << CONT_BITS) | (wchar_t) (b & LO_MASK_8(CONT_BITS));

        cbytes--;

    }

    return ch;

}

/** Encode a single character to string representation.

 *

 * Encode a single character to string representation (i.e. UTF-8) and store

 * it into a buffer at @a offset. Encoding starts at @a offset and this offset

 * is moved to the position where the next character can be written to.

 *

 * @param ch     Input character.

 * @param str    Output buffer.

 * @param offset Byte offset where to start writing.

 * @param size   Size of the output buffer (in bytes).

 *

 * @return EOK if the character was encoded successfully, EOVERFLOW if there

 *     was not enough space in the output buffer or EINVAL if the character

 *     code was invalid.

 */

int chr_encode(const wchar_t ch, char *str, size_t *offset, size_t size)

{

    if (*offset >= size)

        return EOVERFLOW;

    if (!chr_check(ch))

        return EINVAL;

    /* Unsigned version of ch (bit operations should only be done

       on unsigned types). */

    uint32_t cc = (uint32_t) ch;

    /* Determine how many continuation bytes are needed */

    unsigned int b0_bits;  /* Data bits in first byte */

    unsigned int cbytes;   /* Number of continuation bytes */

    if ((cc & ~LO_MASK_32(7)) == 0) {

        b0_bits = 7;

        cbytes = 0;

    } else if ((cc & ~LO_MASK_32(11)) == 0) {

        b0_bits = 5;

        cbytes = 1;

    } else if ((cc & ~LO_MASK_32(16)) == 0) {

        b0_bits = 4;

        cbytes = 2;

    } else if ((cc & ~LO_MASK_32(21)) == 0) {

        b0_bits = 3;

        cbytes = 3;

    } else {

        /* Codes longer than 21 bits are not supported */

        return EINVAL;

    }

    /* Check for available space in buffer */

    if (*offset + cbytes >= size)

        return EOVERFLOW;

    /* Encode continuation bytes */

    unsigned int i;

    for (i = cbytes; i > 0; i--) {

        str[*offset + i] = 0x80 | (cc & LO_MASK_32(CONT_BITS));

        cc = cc >> CONT_BITS;

    }

    /* Encode first byte */

    str[*offset] = (cc & LO_MASK_32(b0_bits)) | HI_MASK_8(8 - b0_bits - 1);

    /* Advance offset */

    *offset += cbytes + 1;

    return EOK;

}

/** Check whether character is valid

 *

 * @return True if character is a valid Unicode code point.

 *

 */

bool chr_check(const wchar_t ch)

{

    if ((ch >= 0) && (ch <= 1114111))

        return true;

    return false;

}