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Rewrote Sequence::FindBlock, without recursion, and with dictionary search

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This commit is contained in:
Paul Licameli 2016-02-03 12:59:44 -05:00
parent 6c28276daf
commit e6987284e3
2 changed files with 34 additions and 28 deletions
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60
src/Sequence.cpp
View File

@ -1046,40 +1046,48 @@ void Sequence::WriteXML(XMLWriter &xmlFile)
xmlFile.EndTag(wxT("sequence")); xmlFile.EndTag(wxT("sequence"));
} }
int Sequence::FindBlock(sampleCount pos, sampleCount lo,
sampleCount guess, sampleCount hi) const
{
const SeqBlock &block = mBlock.at(guess);
wxASSERT(block.f->GetLength() > 0);
wxASSERT(lo <= guess && guess <= hi && lo <= hi);
if (pos >= block.start &&
pos < block.start + block.f->GetLength())
return guess;
//this is a binary search, but we probably could benefit by something more like
//dictionary search where we guess something smarter than the binary division
//of the unsearched area, since samples are usually proportional to block file number.
if (pos < block.start)
return FindBlock(pos, lo, (lo + guess) / 2, guess);
else
return FindBlock(pos, guess + 1, (guess + 1 + hi) / 2, hi);
}
int Sequence::FindBlock(sampleCount pos) const int Sequence::FindBlock(sampleCount pos) const
{ {
wxASSERT(pos >= 0 && pos <= mNumSamples); wxASSERT(pos >= 0 && pos < mNumSamples);
int numBlocks = mBlock.size();
if (pos == 0) if (pos == 0)
return 0; return 0;
if (pos == mNumSamples) int numBlocks = mBlock.size();
return (numBlocks - 1);
int rval = FindBlock(pos, 0, numBlocks / 2, numBlocks); sampleCount lo = 0, loSamples = 0;
sampleCount hi = numBlocks, hiSamples = mNumSamples;
sampleCount guess;
while (true) {
//this is not a binary search, but a
//dictionary search where we guess something smarter than the binary division
//of the unsearched area, since samples are usually proportional to block file number.
const double frac = double(pos - loSamples) / (hiSamples - loSamples);
guess = std::min(hi - 1, lo + sampleCount(frac * (hi - lo)));
const SeqBlock &block = mBlock.at(guess);
wxASSERT(block.f->GetLength() > 0);
wxASSERT(lo <= guess && guess < hi && lo < hi);
if (pos < block.start) {
wxASSERT(lo != guess);
hi = guess;
hiSamples = block.start;
}
else {
const sampleCount nextStart = block.start + block.f->GetLength();
if (pos < nextStart)
break;
else {
wxASSERT(guess < hi - 1);
lo = guess + 1;
loSamples = nextStart;
}
}
}
const int rval = guess;
wxASSERT(rval >= 0 && rval < numBlocks && wxASSERT(rval >= 0 && rval < numBlocks &&
pos >= mBlock.at(rval).start && pos >= mBlock.at(rval).start &&
pos < mBlock.at(rval).start + mBlock.at(rval).f->GetLength()); pos < mBlock.at(rval).start + mBlock.at(rval).f->GetLength());

2
src/Sequence.h
View File

@ -242,8 +242,6 @@ class Sequence: public XMLTagHandler {
void CalcSummaryInfo(); void CalcSummaryInfo();
int FindBlock(sampleCount pos) const; int FindBlock(sampleCount pos) const;
int FindBlock(sampleCount pos, sampleCount lo,
sampleCount guess, sampleCount hi) const;
bool AppendBlock(const SeqBlock &b); bool AppendBlock(const SeqBlock &b);