DoubleConsts.java

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package jdk.internal.math;

/**
 * This class contains additional constants documenting limits of the {@code double} type.
 *
 * @author Joseph D. Darcy
 */
// 双精度浮点数结构常量
public class DoubleConsts {
    /**
     * The number of logical bits in the significand of a {@code double} number, including the implicit bit.
     */
    
    public static final int SIGNIFICAND_WIDTH = 53; // 符号位和小数位所占的位数之和
    
    /**
     * The exponent the smallest positive {@code double} subnormal value would have if it could be normalized..
     */
    public static final int MIN_SUB_EXPONENT = Double.MIN_EXPONENT - (SIGNIFICAND_WIDTH - 1);
    
    /**
     * Bias used in representing a {@code double} exponent.
     */
    public static final int EXP_BIAS = 1023;    // 指数位偏移量
    
    /**
     * Bit mask to isolate the sign bit of a {@code double}.
     */
    public static final long SIGN_BIT_MASK = 0x8000000000000000L;   // 符号位掩码
    
    /**
     * Bit mask to isolate the exponent field of a {@code double}.
     */
    public static final long EXP_BIT_MASK = 0x7FF0000000000000L;    // 指数位掩码
    
    /**
     * Bit mask to isolate the significand field of a
     * {@code double}.
     */
    public static final long SIGNIF_BIT_MASK = 0x000FFFFFFFFFFFFFL; // 小数位掩码
    
    static {
        // verify bit masks cover all bit positions and that the bit
        // masks are non-overlapping
        assert (
            ((SIGN_BIT_MASK | EXP_BIT_MASK | SIGNIF_BIT_MASK) == ~0L)
                && (
                ((SIGN_BIT_MASK & EXP_BIT_MASK) == 0L)
                    && ((SIGN_BIT_MASK & SIGNIF_BIT_MASK) == 0L)
                    && ((EXP_BIT_MASK & SIGNIF_BIT_MASK) == 0L)
            )
        );
    }
    
    /**
     * Don't let anyone instantiate this class.
     */
    private DoubleConsts() {
    }
}