blob_share_commitment_rules.go

package share

import (
	math "math"

	"golang.org/x/exp/constraints"
)

// BlobMinSquareSize returns the minimum square size that can contain shareCount
// number of shares.
func BlobMinSquareSize(shareCount int) int {
	return RoundUpPowerOfTwo(int(math.Ceil(math.Sqrt(float64(shareCount)))))
}

// SubTreeWidth determines the maximum number of leaves per subtree in the share
// commitment over a given blob. The input should be the total number of shares
// used by that blob. The reasoning behind this algorithm is discussed in depth
// in ADR013
// (celestia-app/docs/architecture/adr-013-non-interative-default-rules-for-zero-padding).
func SubTreeWidth(shareCount, subtreeRootThreshold int) int {
	// per ADR013, we use a predetermined threshold to determine width of sub
	// trees used to create share commitments
	s := (shareCount / subtreeRootThreshold)

	// round up if the width is not an exact multiple of the threshold
	if shareCount%subtreeRootThreshold != 0 {
		s++
	}

	// use a power of two equal to or larger than the multiple of the subtree
	// root threshold
	s = RoundUpPowerOfTwo(s)

	// use the minimum of the subtree width and the min square size, this
	// gurarantees that a valid value is returned
	return min(s, BlobMinSquareSize(shareCount))
}

func min[T constraints.Integer](i, j T) T {
	if i < j {
		return i
	}
	return j
}