github.com/egonelbre/exp@v0.0.0-20240430123955-ed1d3aa93911/niterator/onearrpremul/iterator.go (about)

     1  package onearrpremul
     2  
     3  import (
     4  	"io"
     5  
     6  	"github.com/egonelbre/exp/niterator/shape"
     7  )
     8  
     9  type Index struct {
    10  	Track  uint32
    11  	Shape  uint32
    12  	Stride uint32
    13  	Premul uint32
    14  }
    15  
    16  type Iterator struct {
    17  	*shape.AP
    18  
    19  	Track     []Index
    20  	NextIndex uint32
    21  	Done      bool
    22  }
    23  
    24  func NewIterator(ap *shape.AP) *Iterator {
    25  	track := make([]Index, len(ap.Shape))
    26  	for i := range ap.Shape {
    27  		track[i].Shape = uint32(ap.Shape[i])
    28  		track[i].Stride = uint32(ap.Stride[i])
    29  		track[i].Premul = uint32((ap.Shape[i] - 1) * ap.Stride[i])
    30  	}
    31  
    32  	return &Iterator{
    33  		AP:    ap,
    34  		Track: track,
    35  	}
    36  }
    37  
    38  func (it *Iterator) IsDone() bool {
    39  	return it.Done
    40  }
    41  
    42  func (it *Iterator) Next() (int, error) {
    43  	if it.Done {
    44  		return 0, io.EOF
    45  	}
    46  
    47  	last := len(it.Track) - 1
    48  	next := it.NextIndex
    49  	result := next
    50  
    51  	// the following 3 lines causes the compiler to perform bounds check here,
    52  	// instead of being done in the loop
    53  	track := it.Track[:last+1]
    54  	for i := last; i >= 0; i-- {
    55  		x := &track[i]
    56  		x.Track++
    57  		if x.Track == x.Shape {
    58  			if i == 0 {
    59  				it.Done = true
    60  			}
    61  			x.Track = 0
    62  			next -= x.Premul
    63  			continue
    64  		}
    65  		next += x.Stride
    66  		break
    67  	}
    68  	it.NextIndex = next
    69  	return int(result), nil
    70  }