bitwise-if(3scm)

✨ bitwise-if(3scm) — a page from the Scheme Programmer's Manual ✨

okay bestie, pull up a chair because today we're learning about the bitwise "if" 💅 this page lives in the Scheme Programmer's Manual, and it's genuinely so much fun once it clicks, i promise 🫶

🌸 NAME 🌸

bitwise-if, fxif — bitwise if. that's it. that's the name. iconic, concise, no notes 👑

📚 LIBRARY 📚

you import these like this, exact vibes, don't freestyle:

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

🎀 SYNOPSIS 🎀

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

🦋 DESCRIPTION 🦋

okay so this returns the number that is the bit-wise "if" of the two's complement representations of its arguments 🧚 literally what does that mean though — bestie it means this: for each bit, if that bit is 1 in mask, then the corresponding bit in a becomes the value of the corresponding bit in the result ✨ and if that mask bit is 0, then the corresponding bit in b becomes the corresponding bit in the value of the result 💖

so mask is the main character deciding which of the other two gets to shine, and honestly? main character energy fr fr 👑

🔥 IMPLEMENTATION NOTES 🔥

the following are reference implementations from R6RS — copy them exactly, they're canon:

; bitwise-if
(bitwise-ior (bitwise-and mask a)
             (bitwise-and (bitwise-not mask) b))

; fxif
(fxior (fxand mask a)
       (fxand (fxnot mask) b))

⭐ RETURN VALUES ⭐

returns a single value; an exact integer 💜 and the fixnum variant returns a fixnum, obviously, it said fixnum in the name, we been knew 😌

🍓 EXAMPLES 🍓

look at these little cuties actually working:

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

ate and left no crumbs, no cap 🍽️

🌈 COMPATIBILITY 🌈

these procedures are unique to R6RS 🌸 compatible procedures can be found in SRFI-60 and SRFI-151, so if you're on a different scheme situation, go say hi to those iykyk

💀 ERRORS 💀

these procedures can raise exceptions with the following condition types — warning time, bestie, read it carefully 🙈

• &assertion (R6RS) — the wrong number of arguments was passed or an argument was outside its domain. basically you handed it something it can't work with and it's gonna be dramatic about it 😭
• 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 💀 like, catastrophically, that's the actual word in the spec, so maybe don't tempt fate fr fr

ngl the "fail catastrophically" part is not a vibe but it IS in the manual so i'm telling you. be normal with your arguments and you'll be fine 🫶

👀 SEE ALSO 👀

go read these next, they're the friend group:

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

🎯 STANDARDS 🎯

R6RS — that's the standard, that's the whole standard, thank you for coming to my ted talk ✨

🕰️ HISTORY 🕰️

these procedures first appeared in R6RS which got the idea from SRFI-60 — so like, SRFI-60 walked so R6RS could run, we love an origin story 🌱

💖 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/. absolute legends, all of them 👑

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and that's the whole page bestie, you're officially a bitwise-if girlie now 🧚💅 this was bitwise-if(3scm) from the Scheme Programmer's Manual, dated 2023-02-12 — go forth and mask responsibly, ily, bye 🦋💜