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package blake3
import (
"fmt"
"io"
"unsafe"
"github.com/zeebo/blake3/internal/alg"
"github.com/zeebo/blake3/internal/consts"
"github.com/zeebo/blake3/internal/utils"
)
// Digest captures the state of a Hasher allowing reading and seeking through
// the output stream.
type Digest struct {
counter uint64
chain [8]uint32
block [16]uint32
blen uint32
flags uint32
buf [16]uint32
bufn int
}
// Read reads data frm the hasher into out. It always fills the entire buffer and
// never errors. The stream will wrap around when reading past 2^64 bytes.
func (d *Digest) Read(p []byte) (n int, err error) {
n = len(p)
if d.bufn > 0 {
n := d.slowCopy(p)
p = p[n:]
d.bufn -= n
}
for len(p) >= 64 {
d.fillBuf()
if consts.IsLittleEndian {
*(*[64]byte)(unsafe.Pointer(&p[0])) = *(*[64]byte)(unsafe.Pointer(&d.buf[0]))
} else {
utils.WordsToBytes(&d.buf, p)
}
p = p[64:]
d.bufn = 0
}
if len(p) == 0 {
return n, nil
}
d.fillBuf()
d.bufn -= d.slowCopy(p)
return n, nil
}
// Seek sets the position to the provided location. Only SeekStart and
// SeekCurrent are allowed.
func (d *Digest) Seek(offset int64, whence int) (int64, error) {
switch whence {
case io.SeekStart:
case io.SeekEnd:
return 0, fmt.Errorf("seek from end not supported")
case io.SeekCurrent:
offset += int64(consts.BlockLen*d.counter) - int64(d.bufn)
default:
return 0, fmt.Errorf("invalid whence: %d", whence)
}
if offset < 0 {
return 0, fmt.Errorf("seek before start")
}
d.setPosition(uint64(offset))
return offset, nil
}
func (d *Digest) setPosition(pos uint64) {
d.counter = pos / consts.BlockLen
d.fillBuf()
d.bufn -= int(pos % consts.BlockLen)
}
func (d *Digest) slowCopy(p []byte) (n int) {
off := uint(consts.BlockLen-d.bufn) % consts.BlockLen
if consts.IsLittleEndian {
n = copy(p, (*[consts.BlockLen]byte)(unsafe.Pointer(&d.buf[0]))[off:])
} else {
var tmp [consts.BlockLen]byte
utils.WordsToBytes(&d.buf, tmp[:])
n = copy(p, tmp[off:])
}
return n
}
func (d *Digest) fillBuf() {
alg.Compress(&d.chain, &d.block, d.counter, d.blen, d.flags, &d.buf)
d.counter++
d.bufn = consts.BlockLen
}
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