Re: review request for 6798511/6860431: Include functionality of Surrogate in Character

[Ulf Zibis]

Am 26.08.2009 20:02, schrieb Xueming Shen:

For example, the isBMP(int), it might be convenient, but it can be easily archived by the one line code

(int)(char)codePoint == codePoint;

or more readable form

   codePoint < Character.MIN_SUPPLEMENTARY_COE_POINT;

In class sun.nio.cs.Surrogate we have:
    public static boolean isBMP(int uc) {
        return (int) (char) uc == uc;
    }

1.) It's enough to have:
        return (char)uc == uc;
    better:
        assert MIN_VALUE == 0 && MAX_VALUE == 0xFFFF;
        return (char)uc == uc;
        // Optimized form of: uc >= MIN_VALUE && uc <= MAX_VALUE

2.) Above code is compiled to (needs 16 bytes of machine code):
  0x00b87ad8: mov    %ebx,%ebp
  0x00b87ada: and    $0xffff,%ebp
  0x00b87ae0: cmp    %ebx,%ebp
  0x00b87ae2: jne    0x00b87c52
  0x00b87ae8:

    We could code:
        assert MIN_VALUE == 0 && (MAX_VALUE + 1) == (1 << 16);
        return (uc >> 16) == 0;
        // Optimized form of: uc >= MIN_VALUE && uc <= MAX_VALUE

    is compiled to (needs only 9 bytes of machine code):
  0x00b87aac: mov    %ebx,%ecx
  0x00b87aae: sar    $0x10,%ecx
  0x00b87ab1: test   %ecx,%ecx
  0x00b87ab3: je     0x00b87acb
  0x00b87ab5:

1.) If we have:
    public static boolean isSupplementaryCodePoint(int codePoint) {
        assert MIN_SUPPLEMENTARY_CODE_POINT == (1 << 16) &&
                (MAX_SUPPLEMENTARY_CODE_POINT + 1) % (1 << 16) == 0;
        return (codePoint >> 16) != 0
&& (codePoint >> 16) < (MAX_SUPPLEMENTARY_CODE_POINT + 1 >> 16);
        // Optimized form of: codePoint >= MIN_SUPPLEMENTARY_CODE_POINT
        // && codePoint <= MAX_SUPPLEMENTARY_CODE_POINT;
    }
and:
        if (Surrogate.isBMP(uc))
            ...;
        else if (Character.isSupplementaryCodePoint(uc))
            ...;
        else
            ...;

    we get (needs only 18 bytes of machine code):
  0x00b87aac: mov    %ebx,%ecx
  0x00b87aae: sar    $0x10,%ecx
  0x00b87ab1: test   %ecx,%ecx
  0x00b87ab3: je     0x00b87acb
  0x00b87ab5: cmp    $0x11,%ecx
  0x00b87ab8: jge    0x00b87ce6
  0x00b87abe:


-Ulf