bitwise-bit-set?(3scm)

📦 version 0-unstable-2024-02, in nixpkgs unstable

💅 bitwise-bit-set?(3scm) — hi bestie, welcome to the Scheme Programmer's Manual ✨

okay so this page is your whole guide to bitwise-bit-set? and fxbit-set?, which live in the Scheme Programmer's Manual (3scm, if you're keeping score 🎀). and yes, it's serving exactly the "is this one single bit alive" energy you'd expect. let's get into it 💖

🌸 NAME 🌸

bitwise-bit-set?, fxbit-set? — test if a bit is set in an exact integer. that's it, that's the job, and honestly? she ate 👑

💜 LIBRARY 💜

three different doors into the same party, pick whichever import your code already has open:

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

🦋 SYNOPSIS 🦋

(bitwise-bit-set? ei k)
(fxbit-set? fx k)

two procedures, two arguments each, no drama ✨

🧚 DESCRIPTION 🧚

okay so the whole vibe: these return #t if the kth bit is 1 in the two's complement representation of ei or fx respectively, and #f otherwise. that's the entire function, no cap. you hand it a number and a bit index, it tells you if that bit is turned on. bit goes brrr or it doesn't 💅

and because the spec loves being extra, here's the literal result of the following computation — like, this is genuinely what it's computing:

; bitwise-bit-set?
(not (zero? (bitwise-and (bitwise-arithmetic-shift-left 1 k)
                         ei)))

; fxbit-set?
(if (fx>=? k (fx- (fixnum-width) 1))
    (fxnegative? fx)
    (not (fxzero? (fxand fx (fxarithmetic-shift-left 1 k)))))

so the fixnum one has that cheeky little conditional at the top for the top bit — iconic behavior, honestly 🫶

🎀 RETURN VALUES 🎀

Returns a single boolean object. one value. a #t or a #f. that's it. lowkey the cleanest return contract ever 💀

⭐ EXAMPLES ⭐

watch her work:

(bitwise-bit-set? #b101 0)
          =>  #t

(bitwise-bit-set? #b101 1)
          =>  #f

bit 0 is set in #b101, bit 1 is not. slay. look at the binary, it's right there: 101 🔥

🌈 COMPATIBILITY 🌈

This procedure is new in R6RS. also, SRFI-151 has the similar procedure bit-set?. so if you're on a different SRFI situation, you know where to look 👀 iykyk

💀 ERRORS 💀

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. Raised if k is negative. ⚠️ yeah, negative k is a no from her, like don't even try it

🔥 SEE ALSO 🔥

go read the neighbors, they're all lovely:

👑 STANDARDS 👑

R6RS. periodt 💅

🌟 AUTHORS 🌟

This page is part of the scheme-manpages project. It includes materials from the RnRS documents. More information can be found at https://github.com/schemedoc/manpages/. genuine main character energy from the docs team fr fr 🫶

🙈 BUGS 🙈

Note that even in the fixnum variant, k is allowed to be greater than the fixnum width. There have been bugs related to this aspect in Sagittarius 0.4.9 and IronScheme TFS:101169. so like... she's a little wild past the fixnum width, and yes, people have been burned 😭 noted and documented, at least

okay that's the page!! manual bitwise-bit-set?(3scm), dated 2021-03-09, from the scheme-manpages project — go forth, check your bits, and remember: no negative k 🎀✨💖

📦 where this page comes from