SRFI 60: Integers as Bits
This egg provides the SRFI 60 bitwise library, implemented as a very thin wrapper on top of bitwise-utils. Every form that appears here can be found in bitwise-utils under a different name, and srfi-151 (the successor to SRFI 60) provides many operations not found in either egg. There's not much reason to use this library.
This page is intended to document the forms provided by this egg. For a full description of SRFI 60, see the SRFI document.
- logand n1 ...procedure
- bitwise-and n1 ...procedure
Returns the integer which is the bit-wise AND of the integer arguments.
(number->string (logand #b1100 #b1010) 2) ; => "1000"
- logior n1 ...procedure
- bitwise-ior n1 ...procedure
Returns the integer which is the bit-wise OR of the integer arguments.
(number->string (logior #b1100 #b1010) 2) ; => "1110"
- logxor n1 ...procedure
- bitwise-xor n1 ...procedure
Returns the integer which is the bit-wise XOR of the integer arguments.
(number->string (logxor #b1100 #b1010) 2) ; => "110"
- lognot nprocedure
- bitwise-not nprocedure
Returns the integer which is the one's-complement of the integer argument.
(number->string (lognot #b10000000) 2) ; => "-10000001" (number->string (lognot #b0) 2) ; => "-1"
- bitwise-if mask n0 n1procedure
- bitwise-merge mask n0 n1procedure
Returns an integer composed of some bits from integer n0 and some from integer n1. A bit of the result is taken from n0 if the corresponding bit of integer mask is 1 and from n1 if that bit of mask is 0.
- logtest j kprocedure
- any-bits-set? j kprocedure
(logtest j k) == (not (zero? (logand j k))) (logtest #b0100 #b1011) ; => #f (logtest #b0100 #b0111) ; => #t
- logcount nprocedure
- bit-count nprocedure
Returns the number of bits in integer n. If integer is positive, the 1-bits in its binary representation are counted. If negative, the 0-bits in its two's-complement binary representation are counted. If 0, 0 is returned.
(logcount #b10101010) ; => 4 (logcount 0) ; => 0 (logcount -2) ; => 1
- integer-length nprocedure
Returns the number of bits neccessary to represent n.
(integer-length #b10101010) ; => 8 (integer-length 0) ; => 0 (integer-length #b1111) ; => 4
- log2-binary-factors nprocedure
- first-set-bit nprocedure
Returns the number of factors of two of integer n. This value is also the bit-index of the least-significant 1-bit in n.
Bit Within Word
- logbit? index nprocedure
- bit-set? index nprocedure
(logbit? index n) == (logtest (expt 2 index) n) (logbit? 0 #b1101) ; => #t (logbit? 1 #b1101) ; => #f (logbit? 2 #b1101) ; => #t (logbit? 3 #b1101) ; => #t (logbit? 4 #b1101) ; => #f
- copy-bit index from bitprocedure
Returns an integer the same as from except in the indexth bit, which is 1 if bit is #t and 0 if bit is #f.
(number->string (copy-bit 0 0 #t) 2) ; => "1" (number->string (copy-bit 2 0 #t) 2) ; => "100" (number->string (copy-bit 2 #b1111 #f) 2) ; => "1011"
Field of Bits
- bit-field n start endprocedure
Returns the integer composed of the start (inclusive) through end (exclusive) bits of n. The startth bit becomes the 0-th bit in the result.
(number->string (bit-field #b1101101010 0 4) 2) ; => "1010" (number->string (bit-field #b1101101010 4 9) 2) ; => "10110"
- copy-bit-field to from start endprocedure
Returns an integer the same as to except possibly in the start (inclusive) through end (exclusive) bits, which are the same as those of from. The 0-th bit of from becomes the startth bit of the result.
(number->string (copy-bit-field #b1101101010 0 0 4) 2) ; => "1101100000" (number->string (copy-bit-field #b1101101010 -1 0 4) 2) ; => "1101101111" (number->string (copy-bit-field #b110100100010000 -1 5 9) 2) ; => "110100111110000"
- ash n countprocedure
- arithmetic-shift n countprocedure
Returns an integer equivalent to (inexact->exact (floor (* n (expt 2 count)))).
(number->string (ash #b1 3) 2) ; => "1000" (number->string (ash #b1010 -1) 2) ; => "101"
- rotate-bit-field n count start endprocedure
Returns n with the bit-field from start to end cyclically permuted by count bits towards high-order.
(number->string (rotate-bit-field #b0100 3 0 4) 2) ; => "10" (number->string (rotate-bit-field #b0100 -1 0 4) 2) ; => "10" (number->string (rotate-bit-field #b110100100010000 -1 5 9) 2) ; => "110100010010000" (number->string (rotate-bit-field #b110100100010000 1 5 9) 2) ; => "110100000110000"
- reverse-bit-field n start endprocedure
Returns n with the order of bits start to end reversed.
(number->string (reverse-bit-field #xa7 0 8) 16) ; => "e5"
Bits as Booleans
- integer->list k lenprocedure
- integer->list kprocedure
integer->list returns a list of len booleans corresponding to each bit of the non-negative integer k. #t is coded for each 1; #f for 0. The len argument defaults to (integer-length k)
- list->integer listprocedure
list->integer returns an integer formed from the booleans in the list list, which must be a list of booleans. A 1 bit is coded for each #t; a 0 bit for #f.
integer->list and list->integer are inverses so far as equal? is concerned.
- booleans->integer bool1 ...procedure
Returns the integer coded by the bool1 ... arguments.
About this egg
Originally ported to hygienic Chicken 3 with test suite by Peter Danenberg. Ported to Chicken 5 by Sergey Goldgaber.
Contact: wcm at sigwinch dot xyzzy minus the zy
- Change maintainer, tidy tests and wiki page.
- Registered the srfi-60 feature, linked to source code
- Replaced srfi-60 implementation with that from bitwise-utils
- Using (chicken bitwise) procedures, where possible
- Ported to Chicken 5
- release version 0.3
- adopting trunk/tags directory layout. Tagging version 0.2.
Copyright (C) Aubrey Jaffer (2004, 2005). All Rights Reserved.
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