BIT ARRAYS - Accessors for bit-packed arrays of bits for Forth ============================================ Robert Dickow <> Package bit-arrays Version 1.0.2 - 2018-03-02 This is a simple word lexicon for accessing arrays of bits. The fetching words accept two values, the address of the buffer, and a bit-wise index. The storing words accept a bit value or a boolean value, the address of the buffer, and a bit-wise index. The buffer size should be at least 1 CELLS long. ### Top level words: `BIT@` ( caddr n-index -- n0|1 ) \ given a buffer caddr at offset n-index, returns a value of 1 or 0. `BIT!` ( n caddr n-index -- ) \ given a TRUE|FALSE or 1|0 value for n, store the bit into buffer caddr at offset n-index `BOOL@` ( caddr n-index -- ) \ fetch a TRUE|FALSE value given buffer caddr at offset n-index `BOOL!` ( n caddr n-index -- ) \ convenience word for BIT!, but accepts a value of TRUE as equally valid as a bit value 1. ### Include file bit_arrays.f ### Dependencies none ### Internal public words: `2^` ( n -- 2^n ) \ calculates the nth power of 2, used by the ^2MASKS compiling word, kept for consistency with earlier v 1.0.x `^2MASKS` \ a compiling word to build the bmask lookup table, used internally. `bmask` \ a lookup table created by ^2MASKS, used internally in the top-level words `_BIT@` \ a shared code factoring, probably only useful in the top-level words ### Usage Example (32 bit CELL machines) store a 0 into the 34th bit position in a 64 bit bit array. \ ************ DECIMAL \ create the buffer: CREATE bitbuffer 2 CELLS ALLOT \ initialize buffer to all on bits: 4294967295 DUP bitbuffer DUP ROT ROT ! CELL+ ! \ store a bit at position 34 0 bitbuffer 34 BIT! \ test it: bitbuffer 2@ binary du. decimal \ displays: 1111111111111111111111111111111111011111111111111111111111111111 \ ************ ## Changes 2^ now uses bit shifts instead of a slower calculation in loops. Stack comments and other minor typographical changes. ## Bug Reports Please send suggestions, comments, or bug reports Bob Dickow <> ## Compatibility This lexicon is thought to conform to most Forth standards. It was tested on SwiftForth 3.7.1