bitwise-if, fxif - bitwise if

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

(bitwise-if mask a b)
(fxif mask a b)

Returns the number that is the bit-wise "if" of the two's complement representations of its arguments, i.e. for each bit, if it is 1 in mask, the corresponding bit in a becomes the value of the corresponding bit in the result, and if it is 0, the corresponding bit in b becomes the corresponding bit in the value of the result.

The following are reference implementations from R6RS:

; bitwise-if
(bitwise-ior (bitwise-and mask a)
             (bitwise-and (bitwise-not mask) b))
; fxif
(fxior (fxand mask a)
       (fxand (fxnot mask) b))

Returns a single value; an exact integer. The fixnum variant returns a fixnum.

(bitwise-if #xf0f0 #x1234 #xABCD)  =>  #x1B3D
(bitwise-if #b00111100 #b11110000 #b00001111) => #b00110011

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

These procedures can raise exceptions with the following condition types:

&assertion (R6RS)

The wrong number of arguments was passed or an argument was outside its domain.

R7RS

The assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

bitwise-and(3scm), bitwise-ior(3scm), bitwise-copy-bit(3scm), bitwise-copy-bit-field(3scm)

R6RS

These procedures first appeared in R6RS which got the idea from SRFI-60.

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/.