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-// © 2016 and later: Unicode, Inc. and others.
-// License & terms of use: http://www.unicode.org/copyright.html
-/*
-*******************************************************************************
-* Copyright (C) 2010, International Business Machines
-* Corporation and others. All Rights Reserved.
-*******************************************************************************
-* file name: denseranges.cpp
-* encoding: UTF-8
-* tab size: 8 (not used)
-* indentation:4
-*
-* created on: 2010sep25
-* created by: Markus W. Scherer
-*
-* Helper code for finding a small number of dense ranges.
-*/
-
-#include "unicode/utypes.h"
-#include "denseranges.h"
-
-// Definitions in the anonymous namespace are invisible outside this file.
-namespace {
-
-/**
- * Collect up to 15 range gaps and sort them by ascending gap size.
- */
-class LargestGaps {
-public:
- LargestGaps(int32_t max) : maxLength(max<=kCapacity ? max : kCapacity), length(0) {}
-
- void add(int32_t gapStart, int64_t gapLength) {
- int32_t i=length;
- while(i>0 && gapLength>gapLengths[i-1]) {
- --i;
- }
- if(i<maxLength) {
- // The new gap is now one of the maxLength largest.
- // Insert the new gap, moving up smaller ones of the previous
- // length largest.
- int32_t j= length<maxLength ? length++ : maxLength-1;
- while(j>i) {
- gapStarts[j]=gapStarts[j-1];
- gapLengths[j]=gapLengths[j-1];
- --j;
- }
- gapStarts[i]=gapStart;
- gapLengths[i]=gapLength;
- }
- }
-
- void truncate(int32_t newLength) {
- if(newLength<length) {
- length=newLength;
- }
- }
-
- int32_t count() const { return length; }
- int32_t gapStart(int32_t i) const { return gapStarts[i]; }
- int64_t gapLength(int32_t i) const { return gapLengths[i]; }
-
- int32_t firstAfter(int32_t value) const {
- if(length==0) {
- return -1;
- }
- int32_t minValue=0;
- int32_t minIndex=-1;
- for(int32_t i=0; i<length; ++i) {
- if(value<gapStarts[i] && (minIndex<0 || gapStarts[i]<minValue)) {
- minValue=gapStarts[i];
- minIndex=i;
- }
- }
- return minIndex;
- }
-
-private:
- static const int32_t kCapacity=15;
-
- int32_t maxLength;
- int32_t length;
- int32_t gapStarts[kCapacity];
- int64_t gapLengths[kCapacity];
-};
-
-} // namespace
-
-/**
- * Does it make sense to write 1..capacity ranges?
- * Returns 0 if not, otherwise the number of ranges.
- * @param values Sorted array of signed-integer values.
- * @param length Number of values.
- * @param density Minimum average range density, in 256th. (0x100=100%=perfectly dense.)
- * Should be 0x80..0x100, must be 1..0x100.
- * @param ranges Output ranges array.
- * @param capacity Maximum number of ranges.
- * @return Minimum number of ranges (at most capacity) that have the desired density,
- * or 0 if that density cannot be achieved.
- */
-U_CAPI int32_t U_EXPORT2
-uprv_makeDenseRanges(const int32_t values[], int32_t length,
- int32_t density,
- int32_t ranges[][2], int32_t capacity) {
- if(length<=2) {
- return 0;
- }
- int32_t minValue=values[0];
- int32_t maxValue=values[length-1]; // Assume minValue<=maxValue.
- // Use int64_t variables for intermediate-value precision and to avoid
- // signed-int32_t overflow of maxValue-minValue.
- int64_t maxLength=(int64_t)maxValue-(int64_t)minValue+1;
- if(length>=(density*maxLength)/0x100) {
- // Use one range.
- ranges[0][0]=minValue;
- ranges[0][1]=maxValue;
- return 1;
- }
- if(length<=4) {
- return 0;
- }
- // See if we can split [minValue, maxValue] into 2..capacity ranges,
- // divided by the 1..(capacity-1) largest gaps.
- LargestGaps gaps(capacity-1);
- int32_t i;
- int32_t expectedValue=minValue;
- for(i=1; i<length; ++i) {
- ++expectedValue;
- int32_t actualValue=values[i];
- if(expectedValue!=actualValue) {
- gaps.add(expectedValue, (int64_t)actualValue-(int64_t)expectedValue);
- expectedValue=actualValue;
- }
- }
- // We know gaps.count()>=1 because we have fewer values (length) than
- // the length of the [minValue..maxValue] range (maxLength).
- // (Otherwise we would have returned with the one range above.)
- int32_t num;
- for(i=0, num=2;; ++i, ++num) {
- if(i>=gaps.count()) {
- // The values are too sparse for capacity or fewer ranges
- // of the requested density.
- return 0;
- }
- maxLength-=gaps.gapLength(i);
- if(length>num*2 && length>=(density*maxLength)/0x100) {
- break;
- }
- }
- // Use the num ranges with the num-1 largest gaps.
- gaps.truncate(num-1);
- ranges[0][0]=minValue;
- for(i=0; i<=num-2; ++i) {
- int32_t gapIndex=gaps.firstAfter(minValue);
- int32_t gapStart=gaps.gapStart(gapIndex);
- ranges[i][1]=gapStart-1;
- ranges[i+1][0]=minValue=(int32_t)(gapStart+gaps.gapLength(gapIndex));
- }
- ranges[num-1][1]=maxValue;
- return num;
-}