github.com/onflow/flow-go@v0.35.7-crescendo-preview.23-atree-inlining/ledger/common/bitutils/utils.go (about)

     1  package bitutils
     2  
     3  // ReadBit returns the bit at index `idx` in the byte array `b` (big endian)
     4  // The function panics, if the byte slice is too short.
     5  func ReadBit(b []byte, idx int) int {
     6  	byteValue := int(b[idx>>3])
     7  	idx &= 7
     8  	return (byteValue >> (7 - idx)) & 1
     9  }
    10  
    11  // WriteBit assigns value `v` to the bit at index `i` in the byte array `b`.
    12  // The function panics, if the byte slice is too short. We follow the common
    13  // convention of converting between integer and boolean/bit values:
    14  //   - int value == 0   <=>   false   <=>   bit 0
    15  //   - int value != 0   <=>   true    <=>   bit 1
    16  func WriteBit(b []byte, i int, value int) {
    17  	if value == 0 {
    18  		ClearBit(b, i)
    19  	} else {
    20  		SetBit(b, i)
    21  	}
    22  }
    23  
    24  // SetBit sets the bit at index `i` in the byte array `b`, i.e. it assigns
    25  // value 1 to the bit. The function panics, if the byte slice is too short.
    26  func SetBit(b []byte, i int) {
    27  	byteIndex := i >> 3
    28  	i &= 7
    29  	mask := byte(1 << (7 - i))
    30  	b[byteIndex] |= mask
    31  }
    32  
    33  // ClearBit clears the bit at index `i` in the byte slice `b`, i.e. it assigns
    34  // value 0 to the bit. The function panics, if the byte slice is too short.
    35  func ClearBit(b []byte, i int) {
    36  	byteIndex := i >> 3
    37  	i &= 7
    38  	mask := byte(1 << (7 - i))
    39  	b[byteIndex] &= ^mask
    40  }
    41  
    42  // MakeBitVector allocates a byte slice of minimal size that can hold numberBits.
    43  func MakeBitVector(numberBits int) []byte {
    44  	return make([]byte, MinimalByteSliceLength(numberBits))
    45  }
    46  
    47  // MinimalByteSliceLength returns the minimal length of a byte slice that can store n bits.
    48  func MinimalByteSliceLength(n int) int {
    49  	return (n + 7) >> 3
    50  }