# BIT-SMASHER

Common Lisp library for handling bit vectors, bit vector arithmetic, and type conversions.

Available in Quicklisp as of July 2014 release.

Documentation available at: https://thephoeron.github.io/bit-smasher/

### Supported Platforms

BIT-SMASHER is known to compile and pass all tests with 100% code coverage on the latest 64-bit versions of the following Lisp implementations:

- SBCL
- Clozure CL
- CLISP
- ECL
- ABCL
- Allegro CL

It *does not build* on: - CMUCL

It *has not been tested* on: - LispWorks - Clasp - or other available Common Lisp implementations

### Usage Notes and Limitations

This library was designed to complement the set of functions included in the Common Lisp specification for handling bit-vectors, by adding relevant lookup, conversion, arithmetic, measurement, and predicate functions. For documentation and tutorials on the bit-vector functions included in the Common Lisp standard, please refer to:

- Common Lisp HyperSpec:
- Successful Lisp: Chapter 18

BIT-SMASHER only handles the set of non-negative integers. As such, arithmetic on bit-vectors may not always produce the results you expect---return values of all arithmetic functions are given as the absolute ceiling value in bit-vector. Manual conversion of negative integers, floats, fractions, or complex numbers will trigger an error.

### Examples

The conversion functions allow you to convert universally between bit-vectors, octet-vectors, hexadecimal strings, and non-negative integers.

```
; universal type-casting style functions
(bits<- "F0") => #*11110000
(bits<- 240) => #*11110000
(int<- #*11110000) => 240
; manual conversions without type-checking
(hex->bits "F0") => #*11110000
(int->bits 10) => #*00001010
(octets->bits (int->octets 244)) => #*11110100
; etc., etc...
```

Bit-vectors are returned zero-padded to the next full byte.

```
(bits<- 255) => #*11111111
(bits<- 256) => #*0000000100000000
```

Arithmetic on bit-vectors can be achieved through the functions `bit-sum`

, `bit-difference`

, `bit-product`

, `bit-quotient`

, `bit-floor`

, `bit-ceiling`

, `lshift`

, and `rshift`

. There are also the shorthand macros, `bit+`

, `bit-`

, `bit*`

, `bit/`

, `<<`

, and `>>`

. As stated above, the bit-vector arithmetic functions return the absolute ceiling value of the operation. So,

`(bit- #*0000 #*0010) => #*00000010 ; +2, not -2`

The measurement functions `wide-bit-length`

and `min-bit-length`

tell you the maximum and minimum number of bits needed to store a value, respectively. They operate on bit-vectors, octet-vectors, hexadecimal strings, and non-negative integers.

```
(wide-bit-length 256) => 16
(min-bit-length 256) => 9
```

There is also the measurement function `byte-length`

that returns the total number of bytes required to store an integer, bit-vector, or hexadecimal value; or the actual length of byte vector or simple byte array.

```
(byte-length "A0FF") => 2
(byte-length 65536) => 3
```

In addition to the built-in CL predicate function, `bit-vector-p`

, BIT-SMASHER adds the predicate function `twos-complement-p`

, when you need to test the minimum bit length for the two's complement rule. This is required where padding bit-vectors, octet-vectors, or hex-strings with leading zeros up to a set word-length is expected.

```
(twos-complement-p 256) => NIL
(twos-complement-p 255) => T
```

### License

Copyright © 2014–2017, "the Phoeron" Colin J.E. Lupton and the Contributors. This project is released under the MIT License; please see `bit-smasher/LICENSE`

for more information.

- Author
- "the Phoeron" Colin J.E. Lupton <sysop@thephoeron.com>
- License
- MIT