jdk/src/java.base/share/classes/java/lang/StringCoding.java

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package java.lang;

import jdk.internal.util.Preconditions;
import jdk.internal.vm.annotation.IntrinsicCandidate;

import java.util.function.BiFunction;

/**
 * Utility class for string encoding and decoding.
 */
class StringCoding {

    private StringCoding() { }

    /**
     * Count the number of leading non-zero ascii chars in the range.
     */
    static int countNonZeroAscii(String s) {
        byte[] value = s.value();
        if (s.isLatin1()) {
            return countNonZeroAsciiLatin1(value, 0, value.length);
        } else {
            return countNonZeroAsciiUTF16(value, 0, s.length());
        }
    }

    /**
     * Count the number of non-zero ascii chars in the range.
     */
    private static int countNonZeroAsciiLatin1(byte[] ba, int off, int len) {
        int limit = off + len;
        for (int i = off; i < limit; i++) {
            if (ba[i] <= 0) {
                return i - off;
            }
        }
        return len;
    }

    /**
     * Count the number of leading non-zero ascii chars in the range.
     */
    private static int countNonZeroAsciiUTF16(byte[] ba, int off, int strlen) {
        int limit = off + strlen;
        for (int i = off; i < limit; i++) {
            char c = StringUTF16.charAt(ba, i);
            if (c == 0 || c > 0x7F) {
                return i - off;
            }
        }
        return strlen;
    }

    static boolean hasNegatives(byte[] ba, int off, int len) {
        return countPositives(ba, off, len) != len;
    }

    /**
     * Count the number of leading positive bytes in the range.
     *
     * @implSpec the implementation must return len if there are no negative
     *   bytes in the range. If there are negative bytes, the implementation must return
     *   a value that is less than or equal to the index of the first negative byte
     *   in the range.
     *
     * @param ba a byte array
     * @param off the index of the first byte to start reading from
     * @param len the total number of bytes to read
     * @throws NullPointerException if {@code ba} is null
     * @throws ArrayIndexOutOfBoundsException if the provided sub-range is
     *         {@linkplain Preconditions#checkFromIndexSize(int, int, int, BiFunction) out of bounds}
     */
    static int countPositives(byte[] ba, int off, int len) {
        Preconditions.checkFromIndexSize(
                off, len,
                ba.length,      // Implicit null check on `ba`
                Preconditions.AIOOBE_FORMATTER);
        return countPositives0(ba, off, len);
    }

    @IntrinsicCandidate
    private static int countPositives0(byte[] ba, int off, int len) {
        int limit = off + len;
        for (int i = off; i < limit; i++) {
            if (ba[i] < 0) {
                return i - off;
            }
        }
        return len;
    }

    /**
     * Encodes as many ISO-8859-1 codepoints as possible from the source byte
     * array containing characters encoded in UTF-16, into the destination byte
     * array, assuming that the encoding is ISO-8859-1 compatible.
     *
     * @param sa the source byte array containing characters encoded in UTF-16
     * @param sp the index of the <em>character (not byte!)</em> from the source array to start reading from
     * @param da the target byte array
     * @param dp the index of the target array to start writing to
     * @param len the maximum number of <em>characters (not bytes!)</em> to be encoded
     * @return the total number of <em>characters (not bytes!)</em> successfully encoded
     * @throws NullPointerException if any of the provided arrays is null
     */
    static int encodeISOArray(byte[] sa, int sp,
                              byte[] da, int dp, int len) {
        // This method should tolerate invalid arguments, matching the lenient behavior of the VM intrinsic.
        // Hence, using operator expressions instead of `Preconditions`, which throw on failure.
        int sl;
        if ((sp | dp | len) < 0 ||
                // Halving the length of `sa` to obtain the number of characters:
                sp >= (sl = sa.length >>> 1) ||     // Implicit null check on `sa`
                dp >= da.length) {                  // Implicit null check on `da`
            return 0;
        }
        int minLen = Math.min(len, Math.min(sl - sp, da.length - dp));
        return encodeISOArray0(sa, sp, da, dp, minLen);
    }

    @IntrinsicCandidate
    private static int encodeISOArray0(byte[] sa, int sp,
                                       byte[] da, int dp, int len) {
        int i = 0;
        for (; i < len; i++) {
            char c = StringUTF16.getChar(sa, sp++);
            if (c > '\u00FF')
                break;
            da[dp++] = (byte)c;
        }
        return i;
    }

    /**
     * Encodes as many ASCII codepoints as possible from the source
     * character array into the destination byte array, assuming that
     * the encoding is ASCII compatible.
     *
     * @param sa the source character array
     * @param sp the index of the source array to start reading from
     * @param da the target byte array
     * @param dp the index of the target array to start writing to
     * @param len the maximum number of characters to be encoded
     * @return the total number of characters successfully encoded
     * @throws NullPointerException if any of the provided arrays is null
     */
    static int encodeAsciiArray(char[] sa, int sp,
                                byte[] da, int dp, int len) {
        // This method should tolerate invalid arguments, matching the lenient behavior of the VM intrinsic.
        // Hence, using operator expressions instead of `Preconditions`, which throw on failure.
        if ((sp | dp | len) < 0 ||
                sp >= sa.length ||      // Implicit null check on `sa`
                dp >= da.length) {      // Implicit null check on `da`
            return 0;
        }
        int minLen = Math.min(len, Math.min(sa.length - sp, da.length - dp));
        return encodeAsciiArray0(sa, sp, da, dp, minLen);
    }

    @IntrinsicCandidate
    static int encodeAsciiArray0(char[] sa, int sp,
                                 byte[] da, int dp, int len) {
        int i = 0;
        for (; i < len; i++) {
            char c = sa[sp++];
            if (c >= '\u0080')
                break;
            da[dp++] = (byte)c;
        }
        return i;
    }

}