package jiexi;

public class HexUtils {
    // 十六进制字符快速转换表 (ASCII范围内)
    private static final int[] HEX_VALUES = new int[128];
    static {
        for (int i = 0; i < HEX_VALUES.length; i++) {
            char c = (char) i;
            if (c >= '0' && c <= '9') HEX_VALUES[i] = c - '0';
            else if (c >= 'A' && c <= 'F') HEX_VALUES[i] = 10 + (c - 'A');
            else if (c >= 'a' && c <= 'f') HEX_VALUES[i] = 10 + (c - 'a');
            else HEX_VALUES[i] = -1;
        }
    }

    // 线程安全的字符缓冲区 (初始大小256)
    private static final ThreadLocal<char[]> CHAR_BUF_CACHE = 
        ThreadLocal.withInitial(() -> new char[256]);

    /**
     * 获取线程本地字符缓冲区
     * @return 可复用的char[256]缓冲区
     */
    public static char[] getThreadLocalBuffer() {
        return CHAR_BUF_CACHE.get();
    }

    /**
     * 快速将两个十六进制字符转换为字节
     * @param c1 高位字符 (0-9, A-F, a-f)
     * @param c2 低位字符 (0-9, A-F, a-f)
     * @return 转换后的字节值 (无效字符返回0)
     */
    public static int fastHexToByte(char c1, char c2) {
        int high = (c1 < 128) ? HEX_VALUES[c1] : -1;
        int low = (c2 < 128) ? HEX_VALUES[c2] : -1;
        if (high < 0 || low < 0) return 0;
        return (high << 4) | low;
    }
}