bitwise-copy-bit, fxcopy-bit - copy a bit from an integer onto another integer

(import (rnrs))                     ;R6RS
(import (rnrs arithmetic bitwise))  ;R6RS
(import (rnrs arithmetic fixnums))  ;R6RS

(bitwise-copy-bit n k bit)
(fxcopy-bit n k bit)

Returns the result of replacing the k th bit of n by bit.

The following are reference implementations from R6RS.

;; bitwise-copy-bit
(let ((mask (bitwise-arithmetic-shift-left 1 k)))
  (bitwise-if mask
              (bitwise-arithmetic-shift-left bit k)
              n))
;; fxcopy-bit
(let ((mask (fxarithmetic-shift-left 1 k)))
  (fxif mask
        (fxarithmetic-shift-left bit k)
        n))

Returns a single value; an exact integer.

(bitwise-copy-bit 0 10 1)       =>  1024
(bitwise-copy-bit #x8000 0 1)   =>  #x8001
(bitwise-copy-bit #x8001 15 0)  =>  #x0001

These procedures are unique to R6RS. Similar procedures can be found in SRFI-60 and SRFI-151.

This procedure can raise exceptions with the following condition types:

&assertion (R6RS)

The wrong number of arguments was passed or an argument was outside its domain. In particular, k must be non-negative, and bit must be either 0 or 1. The fixnum variant further requires that n is a fixnum and that k is non-negative and less than (fixnum-width)-1.

bitwise-if(3scm), bitwise-bit-set?(3scm)

R6RS

These procedures first appeared in R6RS. There was previously a similar procedure in SRFI-60, copy-bit.

This page is part of the scheme-manpages project. It includes materials from the RnRS documents. More information can be found at https://weinholt.se/scheme/manpages/.

If k is very large then an implementation might try to allocate an excessive amount of memory. In normal implementations it is expected that all practical values of k are fixnums.