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package com.sun.org.apache.bcel.internal.generic;

SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or TABLESWITCH instruction, depending on whether the match values (int[]) can be sorted with no gaps between the numbers.
Version:$Id: SWITCH.java 1749603 2016-06-21 20:50:19Z ggregory $
/** * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or * TABLESWITCH instruction, depending on whether the match values (int[]) can be * sorted with no gaps between the numbers. * * @version $Id: SWITCH.java 1749603 2016-06-21 20:50:19Z ggregory $ */
public final class SWITCH implements CompoundInstruction { private int[] match; private InstructionHandle[] targets; private Select instruction; private int match_length;
Template for switch() constructs. If the match array can be sorted in ascending order with gaps no larger than max_gap between the numbers, a TABLESWITCH instruction is generated, and a LOOKUPSWITCH otherwise. The former may be more efficient, but needs more space. Note, that the key array always will be sorted, though we leave the original arrays unaltered.
Params:
  • match – array of match values (case 2: ... case 7: ..., etc.)
  • targets – the instructions to be branched to for each case
  • target – the default target
  • max_gap – maximum gap that may between case branches
/** * Template for switch() constructs. If the match array can be * sorted in ascending order with gaps no larger than max_gap * between the numbers, a TABLESWITCH instruction is generated, and * a LOOKUPSWITCH otherwise. The former may be more efficient, but * needs more space. * * Note, that the key array always will be sorted, though we leave * the original arrays unaltered. * * @param match array of match values (case 2: ... case 7: ..., etc.) * @param targets the instructions to be branched to for each case * @param target the default target * @param max_gap maximum gap that may between case branches */
public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target, final int max_gap) { this.match = match.clone(); this.targets = targets.clone(); if ((match_length = match.length) < 2) { instruction = new TABLESWITCH(match, targets, target); } else { sort(0, match_length - 1); if (matchIsOrdered(max_gap)) { fillup(max_gap, target); instruction = new TABLESWITCH(this.match, this.targets, target); } else { instruction = new LOOKUPSWITCH(this.match, this.targets, target); } } } public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target) { this(match, targets, target, 1); } private void fillup( final int max_gap, final InstructionHandle target ) { final int max_size = match_length + match_length * max_gap; final int[] m_vec = new int[max_size]; final InstructionHandle[] t_vec = new InstructionHandle[max_size]; int count = 1; m_vec[0] = match[0]; t_vec[0] = targets[0]; for (int i = 1; i < match_length; i++) { final int prev = match[i - 1]; final int gap = match[i] - prev; for (int j = 1; j < gap; j++) { m_vec[count] = prev + j; t_vec[count] = target; count++; } m_vec[count] = match[i]; t_vec[count] = targets[i]; count++; } match = new int[count]; targets = new InstructionHandle[count]; System.arraycopy(m_vec, 0, match, 0, count); System.arraycopy(t_vec, 0, targets, 0, count); }
Sort match and targets array with QuickSort.
/** * Sort match and targets array with QuickSort. */
private void sort( final int l, final int r ) { int i = l; int j = r; int h; final int m = match[(l + r) / 2]; InstructionHandle h2; do { while (match[i] < m) { i++; } while (m < match[j]) { j--; } if (i <= j) { h = match[i]; match[i] = match[j]; match[j] = h; // Swap elements h2 = targets[i]; targets[i] = targets[j]; targets[j] = h2; // Swap instructions, too i++; j--; } } while (i <= j); if (l < j) { sort(l, j); } if (i < r) { sort(i, r); } }
Returns:match is sorted in ascending order with no gap bigger than max_gap?
/** * @return match is sorted in ascending order with no gap bigger than max_gap? */
private boolean matchIsOrdered( final int max_gap ) { for (int i = 1; i < match_length; i++) { if (match[i] - match[i - 1] > max_gap) { return false; } } return true; } @Override public final InstructionList getInstructionList() { return new InstructionList(instruction); } public final Instruction getInstruction() { return instruction; } }