Simplify BitStorage implement

save/bitstorage.go

@@ -12,90 +12,15 @@ type BitStorage struct {
 
 	bits, size    int
 	valuesPerLong int
-
-	divideMul   int
-	divideAdd   int
-	divideShift int
 }
 
 // NewBitStorage create a new BitStorage, // TODO: document
 func NewBitStorage(bits, size int, arrl []uint64) (b *BitStorage) {
-	var _MAGIC = [...]int{
-		-1, -1, 0,
-		math.MinInt32, 0, 0,
-		1431655765, 1431655765, 0,
-		math.MinInt32, 0, 1,
-		858993459, 858993459, 0,
-		715827882, 715827882, 0,
-		613566756, 613566756, 0,
-		math.MinInt32, 0, 2,
-		477218588, 477218588, 0,
-		429496729, 429496729, 0,
-		390451572, 390451572, 0,
-		357913941, 357913941, 0,
-		330382099, 330382099, 0,
-		306783378, 306783378, 0,
-		286331153, 286331153, 0,
-		math.MinInt32, 0, 3,
-		252645135, 252645135, 0,
-		238609294, 238609294, 0,
-		226050910, 226050910, 0,
-		214748364, 214748364, 0,
-		204522252, 204522252, 0,
-		195225786, 195225786, 0,
-		186737708, 186737708, 0,
-		178956970, 178956970, 0,
-		171798691, 171798691, 0,
-		165191049, 165191049, 0,
-		159072862, 159072862, 0,
-		153391689, 153391689, 0,
-		148102320, 148102320, 0,
-		143165576, 143165576, 0,
-		138547332, 138547332, 0,
-		math.MinInt32, 0, 4,
-		130150524, 130150524, 0,
-		126322567, 126322567, 0,
-		122713351, 122713351, 0,
-		119304647, 119304647, 0,
-		116080197, 116080197, 0,
-		113025455, 113025455, 0,
-		110127366, 110127366, 0,
-		107374182, 107374182, 0,
-		104755299, 104755299, 0,
-		102261126, 102261126, 0,
-		99882960, 99882960, 0,
-		97612893, 97612893, 0,
-		95443717, 95443717, 0,
-		93368854, 93368854, 0,
-		91382282, 91382282, 0,
-		89478485, 89478485, 0,
-		87652393, 87652393, 0,
-		85899345, 85899345, 0,
-		84215045, 84215045, 0,
-		82595524, 82595524, 0,
-		81037118, 81037118, 0,
-		79536431, 79536431, 0,
-		78090314, 78090314, 0,
-		76695844, 76695844, 0,
-		75350303, 75350303, 0,
-		74051160, 74051160, 0,
-		72796055, 72796055, 0,
-		71582788, 71582788, 0,
-		70409299, 70409299, 0,
-		69273666, 69273666, 0,
-		68174084, 68174084, 0,
-		math.MinInt32, 0, 5,
-	}
-
-	n3 := 3 * (64/bits - 1)
 	b = &BitStorage{
 		mask:          1<<bits - 1,
 		bits:          bits,
 		size:          size,
 		valuesPerLong: 64 / bits,
-		divideMul:     _MAGIC[n3+0],
-		divideAdd:     _MAGIC[n3+1],
-		divideShift:   _MAGIC[n3+2],
 	}
 	dataLen := (size + b.valuesPerLong - 1) / b.valuesPerLong
 	if arrl != nil {
@@ -110,7 +35,8 @@ func NewBitStorage(bits, size int, arrl []uint64) (b *BitStorage) {
 }
 
 func (b *BitStorage) cellIndex(n int) int {
-	return int((uint64(uint32(n))*uint64(b.divideMul) + uint64(b.divideAdd)) >> 32 >> b.divideShift)
+	elemPerLong := 64 / b.bits
+	return n / elemPerLong
 }
 
 func (b *BitStorage) Swap(i, v int) (old int) {