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improvements to bit reader

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This commit is contained in:
Alex Yatskov 2019-01-22 19:06:13 -08:00
parent ce9e1b9958
commit 2705d6a506
3 changed files with 42 additions and 13 deletions
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20
formats/dcc/dcc.go
View File

@ -88,52 +88,52 @@ func NewFromReader(reader io.ReadSeeker) (*Sprite, error) {
func readDirectionHeader(reader io.ReadSeeker) (*directionHeader, error) { func readDirectionHeader(reader io.ReadSeeker) (*directionHeader, error) {
r := streaming.NewBitReader(reader) r := streaming.NewBitReader(reader)
codedSize, err := r.ReadBits(32) codedSize, err := r.ReadBitsUnsigned(32)
if err != nil { if err != nil {
return nil, err return nil, err
} }
hasRawPixelEncoding, err := r.ReadBits(1) hasRawPixelEncoding, err := r.ReadBitsUnsigned(1)
if err != nil { if err != nil {
return nil, err return nil, err
} }
compressEqualCells, err := r.ReadBits(1) compressEqualCells, err := r.ReadBitsUnsigned(1)
if err != nil { if err != nil {
return nil, err return nil, err
} }
variable0Bits, err := r.ReadBits(4) variable0Bits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
widthBits, err := r.ReadBits(4) widthBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
heightBits, err := r.ReadBits(4) heightBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
offsetXBits, err := r.ReadBits(4) offsetXBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
offsetYBits, err := r.ReadBits(4) offsetYBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
optionalBytesBits, err := r.ReadBits(4) optionalBytesBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }
codedBytesBits, err := r.ReadBits(4) codedBytesBits, err := r.ReadBitsUnsigned(4)
if err != nil { if err != nil {
return nil, err return nil, err
} }

31
streaming/bitreader.go
View File

@ -15,7 +15,36 @@ func NewBitReader(reader io.Reader) *BitReader {
return &BitReader{reader: reader} return &BitReader{reader: reader}
} }
func (r *BitReader) ReadBits(count int) (uint64, error) { func (r *BitReader) ReadBitsSigned(count int) (int64, error) {
value, err := r.readBits(count)
if err != nil {
return 0, err
}
if count > 0 {
valueMasked := value &^ (1 << uint(count-1))
if valueMasked != value {
return -int64(valueMasked), nil
}
}
return int64(value), nil
}
func (r *BitReader) ReadBitsUnsigned(count int) (uint64, error) {
return r.readBits(count)
}
func (r *BitReader) ReadBitFlag() (bool, error) {
value, err := r.readBits(1)
if err != nil {
return false, err
}
return value == 1, nil
}
func (r *BitReader) readBits(count int) (uint64, error) {
if count > 64 { if count > 64 {
return 0, errors.New("cannot read more than 64 bits at a time") return 0, errors.New("cannot read more than 64 bits at a time")
} }

4
streaming/streaming_test.go
View File

@ -18,13 +18,13 @@ func TestBitReader(t *testing.T) {
r := NewBitReader(bytes.NewReader(data)) r := NewBitReader(bytes.NewReader(data))
readPass := func(c int, v uint64) { readPass := func(c int, v uint64) {
if value, err := r.ReadBits(c); value != v || err != nil { if value, err := r.ReadBitsUnsigned(c); value != v || err != nil {
t.Fail() t.Fail()
} }
} }
readFail := func(c int) { readFail := func(c int) {
if value, err := r.ReadBits(c); value != 0 || err == nil { if value, err := r.ReadBitsUnsigned(c); value != 0 || err == nil {
t.Fail() t.Fail()
} }
} }