 Artifact Content

## Artifact bc261fa076faf0df2b89adec129e33b6d197724e:

```// Package provides a shifted fibonacci encoding of unsigned integers.
//
// http://en.wikipedia.org/wiki/Fibonacci_coding maps positive integers as
// 1 - 11, 2 - 011, 3 - 0011, 4 - 1011, 5 - 00011
//
// Incrementing input by one to allow for zero gives
// 0 - 11, 1 - 011, 2 - 0011, 3 - 1011, 4 - 00011
//
// The codes are then reversed so that they are easily stored in uints
// 0 - 11, 1 - 110, 2 - 1100, 3 - 1101, 4 - 11000
// (so that they are always comparable with each other as there is no need to
//  store the leading number of zeroes which are otherwise required)
package fibonacci

import (
_ "fmt"
"io"
)

type Numbers []uint64

// Returns a slice with fibonacci numbers up to the given length
func New(size int) Numbers {
var fibs Numbers = make(Numbers, size)
copy(fibs, []uint64{1, 1})
for i := 2; i < size; i++ {
fibs[i] = fibs[i-1] + fibs[i-2]
}
return fibs
}

// Returns a fibonacci code for an integer as specified in the package's doc.
func (f Numbers) Code(value uint64) (result uint64, length byte) {
// Increment to encode zero as one
value++

// Find the nearest fibonacci number
for f[length] <= value {
length++
}

// Leading bit that signals the start of a fibonacci-encoded integer
result |= 1

// Find the Zeckendorf's representation by raising a bit for each
// fibonacci number that is less or equal to the difference
// between the value and the previous such number
for i := length - 1; i >= 1; i-- {
result <<= 1
if f[i] <= value {
result |= 1
value -= f[i]
}
}
return
}

// Returns an integer from a fibonacci code as specified in the package's doc.
func (f Numbers) Decode(value uint64) (result uint64, length byte) {
length = 1
// Loop until the lowest two bits are both raised
for (value & 3) != 3 {
// Add the fibonacci number for the current bit if it is raised
if (value & 1) == 1 {
result += f[length]

// We know that the next bit cannot be raised by Zeckendorf's theorem
value >>= 2
length += 2
continue
}

value >>= 1
length++
}
return result + f[length] - 1, length + 1
}

func Writer(target io.Writer) io.Writer {
var enc encoder
enc.Numbers = New(14)
enc.target = target
enc.buffer = enc.backing[:0:len(enc.backing)]
return &enc
}

type encoder struct {
Numbers
target    io.Writer
backing   byte
buffer    []byte
remaining byte
length    byte
}

func (e *encoder) Write(input []byte) (int, error) {
var (
total int
err   error
)

// Flush on a nil slice
if input == nil {
e.backing = byte(e.remaining)
_, err = e.target.Write(e.buffer[:1])
return 0, err
}

for _, currentByte := range input {
// Get the fibonacci code and bit length for the current byte
enc, len := e.Code(uint64(currentByte))

// Add current bits to higher positions
e.remaining |= byte(enc << e.length)

// maximum length of added bits to e.remaining
added := 8 - e.length

// Shift the the encoded value and account for its length
enc >>= added
e.length += len
len -= added

// Not enough bits to write
if e.length < 8 {
// Account for the processed input byte
total++

continue
}

// Clearing e.length is not necessary as it will be overwritten later

// Stage the complete byte for writing
e.buffer = append(e.buffer, byte(e.remaining))

// Stage every full byte from the encoded value for writing
for enc > 128 {
e.buffer = append(e.buffer, byte(enc))
enc >>= 8
len -= 8
}

// Store the remaining bits
e.remaining, e.length = byte(enc), len

// Write the staged bytes
_, err = e.target.Write(e.buffer)

// Abort write on error
if err != nil {
break
}

// Account for the processed input byte
total++

// Clear the buffer
e.buffer = e.buffer[:0]
}
return total, err
}

// func Reader(source io.Reader) io.Reader {
// 	var dec decoder
// 	dec.Numbers = New(16)
// 	dec.source = source
// 	return &dec
// }

// type decoder struct {
// 	Numbers
// 	source io.Reader
// 	buffer uint64
// 	at     byte
// }

// func (d *decoder) Read(output []byte) (int, error) {
// 	var (
// 		total int
// 		err   error
// 	)

// 	// While we have suitable buffered data and enough output space
// 	for (len(output) > 0) && ((d.buffer & (d.buffer >> 1)) > 0) {
// 		val, len := d.Decode(d.buffer)

// 		// Store the decoded byte
// 		output = byte(val)

// 		// Advance the internal and output buffers
// 		output = output[1:]
// 		d.buffer >>= len

// 		// TODO - decrease d.at as well ?

// 		total++
// 	}

// 	// Termination condition
// 	if len(output) == 0 {
// 		return total, nil
// 	}

// 	// count, err := d.source.Read(output)

// 	return total, err
// }

```