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Optimization attempt of findPeriod using binary search #163

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Optimization attempt of findPeriod using binary search #163

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17 changes: 12 additions & 5 deletions src/ace/managers/ptplayer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1059,13 +1059,20 @@ static void printVoices(const tModVoice *pVoices) {
}

static inline UBYTE findPeriod(const UWORD *pPeriods, UWORD uwNote) {
// Find nearest period for a note value
for(UBYTE ubPeriodPos = 0; ubPeriodPos < MOD_PERIOD_TABLE_LENGTH; ++ubPeriodPos) {
if (uwNote >= pPeriods[ubPeriodPos]) {
return ubPeriodPos;
// Find nearest period (equal or lower) for a note value using a binary search lookup
UBYTE ubPeriodPos = 0;
UBYTE maxBound = MOD_PERIOD_TABLE_LENGTH;
while (ubPeriodPos != maxBound) {
UBYTE currentIndex = (ubPeriodPos + maxBound) >> 1;
// if this period is greater, skip 'bottom half' of the array and continue searching
if (pPeriods[currentIndex] > uwNote) {
ubPeriodPos = currentIndex + 1;
}
else { // else, the period we seek is between ubPeriodPos and currentIndex
maxBound = currentIndex;
}
}
return 0;
return ubPeriodPos;
}

static void ptSongStep(void) {
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