## bit-smasher

2022-07-08

Utility library for handling bit vectors, bit vector arithmetic, and universal integer type conversions between bit-vectors, byte-vectors, octals, decimals, and hexadecimal notation.

# 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.common-lisp.dev/bit-smasher/

### Supported Platforms

The current release of BIT-SMASHER *compiles without warning* and passes all
tests on 64-bit versions of the following Lisp implementations:

- SBCL 2.2.5
- Clozure CL 1.12.1
- CLISP 2.49.92
- ABCL 1.9.0
- Allegro CL 10.1

It *compiles with warnings* on:

- LispWorks 8.0.1

It *compiles with style-warnings* on:

- ECL 21.2.1

It *does not build* on:

- CLASP CL 1.0.0 (clasp-boehmprecise-1.0.0-316-gf3b9992a5)
- CMUCL 21d

### 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 bit-vector of the absolute ceiling value. 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 © 2014–2022, "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.