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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * accompanied this code).
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package com.sun.tools.javac.util;

import java.util.Arrays;

/** A class for extensible, mutable bit sets.
 *
 *  

This is NOT part of any supported API. * If you write code that depends on this, you do so at your own risk. * This code and its internal interfaces are subject to change or * deletion without notice. */ public class Bits { // ____________ reset _________ // / UNKNOWN \ <-------- / UNINIT \ // \____________/ | \_________/ // | | | // |assign | | any // | ___________ | // ------> / NORMAL \ <---- // \___________/ | // | | // | | // ----------- // any protected enum BitsState { /* A Bits instance is in UNKNOWN state if it has been explicitly reset. * It is possible to get to this state from any other by calling the * reset method. An instance in the UNKNOWN state can pass to the * NORMAL state after being assigned another Bits instance. * * Bits instances are final fields in Flow so the UNKNOWN state models * the null assignment. */ UNKNOWN, /* A Bits instance is in UNINIT when it is created with the default * constructor but it isn't explicitly reset. The main objective of this * internal state is to save some memory. */ UNINIT, /* The normal state is reached after creating a Bits instance from an * existing one or after applying any operation to an instance on UNINIT * or NORMAL state. From this state a bits instance can pass to the * UNKNOWN state by calling the reset method. */ NORMAL; static BitsState getState(int[] someBits, boolean reset) { if (reset) { return UNKNOWN; } else { if (someBits != unassignedBits) { return NORMAL; } else { return UNINIT; } } } } private final static int wordlen = 32; private final static int wordshift = 5; private final static int wordmask = wordlen - 1; public int[] bits = null; // This field will store last version of bits after every change. private static final int[] unassignedBits = new int[0]; protected BitsState currentState; /** Construct an initially empty set. */ public Bits() { this(false); } public Bits(Bits someBits) { this(someBits.dup().bits, BitsState.getState(someBits.bits, false)); } public Bits(boolean reset) { this(unassignedBits, BitsState.getState(unassignedBits, reset)); } /** Construct a set consisting initially of given bit vector. */ protected Bits(int[] bits, BitsState initState) { this.bits = bits; this.currentState = initState; switch (initState) { case UNKNOWN: this.bits = null; break; case NORMAL: Assert.check(bits != unassignedBits); break; } } protected void sizeTo(int len) { if (bits.length < len) { bits = Arrays.copyOf(bits, len); } } /** This set = {}. */ public void clear() { Assert.check(currentState != BitsState.UNKNOWN); for (int i = 0; i < bits.length; i++) { bits[i] = 0; } currentState = BitsState.NORMAL; } public void reset() { internalReset(); } protected void internalReset() { bits = null; currentState = BitsState.UNKNOWN; } public boolean isReset() { return currentState == BitsState.UNKNOWN; } public Bits assign(Bits someBits) { bits = someBits.dup().bits; currentState = BitsState.NORMAL; return this; } /** Return a copy of this set. */ public Bits dup() { Assert.check(currentState != BitsState.UNKNOWN); Bits tmp = new Bits(); tmp.bits = dupBits(); currentState = BitsState.NORMAL; return tmp; } protected int[] dupBits() { int [] result; if (currentState != BitsState.NORMAL) { result = bits; } else { result = new int[bits.length]; System.arraycopy(bits, 0, result, 0, bits.length); } return result; } /** Include x in this set. */ public void incl(int x) { Assert.check(currentState != BitsState.UNKNOWN); Assert.check(x >= 0, "Value of x " + x); sizeTo((x >>> wordshift) + 1); bits[x >>> wordshift] = bits[x >>> wordshift] | (1 << (x & wordmask)); currentState = BitsState.NORMAL; } /** Include [start..limit) in this set. */ public void inclRange(int start, int limit) { Assert.check(currentState != BitsState.UNKNOWN); sizeTo((limit >>> wordshift) + 1); for (int x = start; x < limit; x++) { bits[x >>> wordshift] = bits[x >>> wordshift] | (1 << (x & wordmask)); } currentState = BitsState.NORMAL; } /** Exclude [start...end] from this set. */ public void excludeFrom(int start) { Assert.check(currentState != BitsState.UNKNOWN); Bits temp = new Bits(); temp.sizeTo(bits.length); temp.inclRange(0, start); internalAndSet(temp); currentState = BitsState.NORMAL; } /** Exclude x from this set. */ public void excl(int x) { Assert.check(currentState != BitsState.UNKNOWN); Assert.check(x >= 0); sizeTo((x >>> wordshift) + 1); bits[x >>> wordshift] = bits[x >>> wordshift] & ~(1 << (x & wordmask)); currentState = BitsState.NORMAL; } /** Is x an element of this set? */ public boolean isMember(int x) { Assert.check(currentState != BitsState.UNKNOWN); return 0 <= x && x < (bits.length << wordshift) && (bits[x >>> wordshift] & (1 << (x & wordmask))) != 0; } /** {@literal this set = this set & xs}. */ public Bits andSet(Bits xs) { Assert.check(currentState != BitsState.UNKNOWN); internalAndSet(xs); currentState = BitsState.NORMAL; return this; } protected void internalAndSet(Bits xs) { Assert.check(currentState != BitsState.UNKNOWN); sizeTo(xs.bits.length); for (int i = 0; i < xs.bits.length; i++) { bits[i] = bits[i] & xs.bits[i]; } } /** this set = this set | xs. */ public Bits orSet(Bits xs) { Assert.check(currentState != BitsState.UNKNOWN); sizeTo(xs.bits.length); for (int i = 0; i < xs.bits.length; i++) { bits[i] = bits[i] | xs.bits[i]; } currentState = BitsState.NORMAL; return this; } /** this set = this set \ xs. */ public Bits diffSet(Bits xs) { Assert.check(currentState != BitsState.UNKNOWN); for (int i = 0; i < bits.length; i++) { if (i < xs.bits.length) { bits[i] = bits[i] & ~xs.bits[i]; } } currentState = BitsState.NORMAL; return this; } /** this set = this set ^ xs. */ public Bits xorSet(Bits xs) { Assert.check(currentState != BitsState.UNKNOWN); sizeTo(xs.bits.length); for (int i = 0; i < xs.bits.length; i++) { bits[i] = bits[i] ^ xs.bits[i]; } currentState = BitsState.NORMAL; return this; } /** Count trailing zero bits in an int. Algorithm from "Hacker's * Delight" by Henry S. Warren Jr. (figure 5-13) */ private static int trailingZeroBits(int x) { Assert.check(wordlen == 32); if (x == 0) { return 32; } int n = 1; if ((x & 0xffff) == 0) { n += 16; x >>>= 16; } if ((x & 0x00ff) == 0) { n += 8; x >>>= 8; } if ((x & 0x000f) == 0) { n += 4; x >>>= 4; } if ((x & 0x0003) == 0) { n += 2; x >>>= 2; } return n - (x&1); } /** Return the index of the least bit position ≥ x that is set. * If none are set, returns -1. This provides a nice way to iterate * over the members of a bit set: *

{@code
     *  for (int i = bits.nextBit(0); i>=0; i = bits.nextBit(i+1)) ...
     *  }
*/ public int nextBit(int x) { Assert.check(currentState != BitsState.UNKNOWN); int windex = x >>> wordshift; if (windex >= bits.length) { return -1; } int word = bits[windex] & ~((1 << (x & wordmask))-1); while (true) { if (word != 0) { return (windex << wordshift) + trailingZeroBits(word); } windex++; if (windex >= bits.length) { return -1; } word = bits[windex]; } } /** a string representation of this set. */ @Override public String toString() { if (bits != null && bits.length > 0) { char[] digits = new char[bits.length * wordlen]; for (int i = 0; i < bits.length * wordlen; i++) { digits[i] = isMember(i) ? '1' : '0'; } return new String(digits); } else { return "[]"; } } /** Test Bits.nextBit(int). */ public static void main(String[] args) { java.util.Random r = new java.util.Random(); Bits bits = new Bits(); for (int i=0; i<125; i++) { int k; do { k = r.nextInt(250); } while (bits.isMember(k)); System.out.println("adding " + k); bits.incl(k); } int count = 0; for (int i = bits.nextBit(0); i >= 0; i = bits.nextBit(i+1)) { System.out.println("found " + i); count ++; } if (count != 125) { throw new Error(); } } }




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