65 lines
1.5 KiB
Go
65 lines
1.5 KiB
Go
package bits
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import (
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"math/big"
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"github.com/cockroachdb/errors"
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)
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// Range has a start and end
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type Range struct {
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Start Bitmap
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End Bitmap
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}
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func MaxRange() Range {
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return Range{
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Start: Bitmap{},
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End: MaxP(),
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}
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}
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// IntervalP divides the range into `num` intervals and returns the `n`th one
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// intervals are approximately the same size, but may not be exact because of rounding issues
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// the first interval always starts at the beginning of the range, and the last interval always ends at the end
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func (r Range) IntervalP(n, num int) Range {
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if num < 1 || n < 1 || n > num {
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panic(errors.WithStack(errors.Newf("invalid interval %d of %d", n, num)))
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}
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start := r.intervalStart(n, num)
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end := r.End.Big()
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if n < num {
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end = r.intervalStart(n+1, num)
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end.Sub(end, big.NewInt(1))
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}
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return Range{FromBigP(start), FromBigP(end)}
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}
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func (r Range) intervalStart(n, num int) *big.Int {
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// formula:
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// size = (end - start) / num
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// rem = (end - start) % num
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// intervalStart = rangeStart + (size * n-1) + ((rem * n-1) % num)
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size := new(big.Int)
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rem := new(big.Int)
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size.Sub(r.End.Big(), r.Start.Big()).DivMod(size, big.NewInt(int64(num)), rem)
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size.Mul(size, big.NewInt(int64(n-1)))
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rem.Mul(rem, big.NewInt(int64(n-1))).Mod(rem, big.NewInt(int64(num)))
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start := r.Start.Big()
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start.Add(start, size).Add(start, rem)
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return start
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}
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func (r Range) IntervalSize() *big.Int {
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return (&big.Int{}).Sub(r.End.Big(), r.Start.Big())
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}
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func (r Range) Contains(b Bitmap) bool {
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return r.Start.Cmp(b) <= 0 && r.End.Cmp(b) >= 0
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}
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