Source file src/github.com/boombuler/barcode/utils/galoisfield.go

Documentation: github.com/boombuler/barcode/utils

     1  package utils
     2  
     3  // GaloisField encapsulates galois field arithmetics
     4  type GaloisField struct {
     5  	Size    int
     6  	Base    int
     7  	ALogTbl []int
     8  	LogTbl  []int
     9  }
    10  
    11  // NewGaloisField creates a new galois field
    12  func NewGaloisField(pp, fieldSize, b int) *GaloisField {
    13  	result := new(GaloisField)
    14  
    15  	result.Size = fieldSize
    16  	result.Base = b
    17  	result.ALogTbl = make([]int, fieldSize)
    18  	result.LogTbl = make([]int, fieldSize)
    19  
    20  	x := 1
    21  	for i := 0; i < fieldSize; i++ {
    22  		result.ALogTbl[i] = x
    23  		x = x * 2
    24  		if x >= fieldSize {
    25  			x = (x ^ pp) & (fieldSize - 1)
    26  		}
    27  	}
    28  
    29  	for i := 0; i < fieldSize; i++ {
    30  		result.LogTbl[result.ALogTbl[i]] = int(i)
    31  	}
    32  
    33  	return result
    34  }
    35  
    36  func (gf *GaloisField) Zero() *GFPoly {
    37  	return NewGFPoly(gf, []int{0})
    38  }
    39  
    40  // AddOrSub add or substract two numbers
    41  func (gf *GaloisField) AddOrSub(a, b int) int {
    42  	return a ^ b
    43  }
    44  
    45  // Multiply multiplys two numbers
    46  func (gf *GaloisField) Multiply(a, b int) int {
    47  	if a == 0 || b == 0 {
    48  		return 0
    49  	}
    50  	return gf.ALogTbl[(gf.LogTbl[a]+gf.LogTbl[b])%(gf.Size-1)]
    51  }
    52  
    53  // Divide divides two numbers
    54  func (gf *GaloisField) Divide(a, b int) int {
    55  	if b == 0 {
    56  		panic("divide by zero")
    57  	} else if a == 0 {
    58  		return 0
    59  	}
    60  	return gf.ALogTbl[(gf.LogTbl[a]-gf.LogTbl[b])%(gf.Size-1)]
    61  }
    62  
    63  func (gf *GaloisField) Invers(num int) int {
    64  	return gf.ALogTbl[(gf.Size-1)-gf.LogTbl[num]]
    65  }
    66  

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