about

Based on John Gustafson's unum ("Right Sizing Precision"), package unum provides variable length, tagged value, encoding of numeric values.

This implementation (as of now) only supports unsigned integers.

spec

general encoding schema

 byte order:  big-endian
 tag-bits:    high-order bits of first byte
 alignment:   byte aligned

---

UNUM-64

The 2-bit tag determines the value-range and physical length of the image:

 tag        | bytes | range
 -----------+-------+------------------------------------------------
 00         | 1     | uint: (0, 2^6] 
 -----------+-------+------------------------------------------------
 01         | 2     | uint: (2^6, 2^14] 
 -----------+-------+------------------------------------------------
 10         | 4     | uint: (2^14, 2^30] 
 -----------+-------+------------------------------------------------
 11         | 8     | uint: (2^30, 2^62] 

examples

uint64 :: 0x3b
[]byte :: {0x3b}

uint64 :: 0x3bab
[]byte :: {0x7b, 0xab}

uint64 :: 0x32febaab
[]byte :: {0xb2, 0xfe, 0xba, 0xab}

uint64 :: 0x197f5d552fe8d5bc
[]byte :: {0xd9, 0x7f, 0x5d, 0x55, 0x2f, 0xe8, 0xd5, 0xbc}

---

UNUM-32

The 2-bit tag determines the value-range and physical length of the image:

 tag        | bytes | range
 -----------+-------+------------------------------------------------
 00         | 1     | uint: (0, 2^6] 
 -----------+-------+------------------------------------------------
 01         | 2     | uint: (2^6, 2^14] 
 -----------+-------+------------------------------------------------
 10         | 3     | uint: (2^14, 2^22] 
 -----------+-------+------------------------------------------------
 11         | 4     | uint: (2^22, 2^30] 

examples

uint32 :: 0x3b
[]byte :: {0x3b}

uint32 :: 0x3bab
[]byte :: {0x7b, 0xab}

uint32 :: 0x2a35c4
[]byte :: {0xaa, 0x35, 0xc4}

uint32 :: 0x2fe8d5bc
[]byte :: {0xef, 0xe8, 0xd5, 0xbc}

---

UNUM-16

The 1-bit tag determines the value-range and physical length of the image:

 tag        | bytes | range
 -----------+-------+------------------------------------------------
 0          | 1     | uint: (0, 2^7] 
 -----------+-------+------------------------------------------------
 1          | 2     | uint: (2^7, 2^15] 

examples

uint16 :: 0x4b
[]byte :: {0x4b}

uint16 :: 0x42fe
[]byte :: {0xc2, 0xfe}

---

usage

Note: Examples below use UNUM-64 encoding but the usage pattern is uniformly applicable.

encode

using byte array

var value []uint64 = { .. }         
var b []byte = ..           // provided by you

// encoding to a byte buffer
var offset int
for _, v := range values {
    n, e := unum.EncodeUint(b[offset:], v)
    if e != nil {
        /* if e is ErrorBufferOverflow you could resize the buffer here */
        break
    }
    offset += n
}

**using io.Writer **

var w Writer = ..           // provider by you
// encoding to a Writer
for _, v := range values {
	_, e := unum.WriteUint(w, v)
	if e != nil {
		log.Fatalf("err - %s - value:%0x", e.Error(), v)
	}
}

decode

using byte array

var b []byte = ..           // unum encoded buffer provided by you

// decoding from a byte buffer
var offset int
for {
    v, n, e := unum.DecodeUint(b[offset:])
    if e != nil {
        break 
    }
    offset += n
}

---

License

The MIT License (MIT)

Copyright (c) 2016 Joubin Muhammad Houshyar

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.