fixasin(3)

🌸 NAME 🌸

fixasin — fixed point inverse sine lookup table 🎀 and it lives in the Allegro game programming library, periodt.

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✨ SYNOPSIS ✨

#include <allegro.h>

fixed fixasin(fixed x);

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💅 DESCRIPTION 💅

okay so bestie, here's the tea ☕ — this function finds the inverse sine of a value, and it does it with a lookup table, not by doing any fancy math on the fly. iykyk.

The input value must be a fixed point value. like, that's not optional, that's the whole vibe.

The inverse sine is defined only in the domain from -1 to 1. that's it. that's the range of inputs it will accept. 🫶

🚨 BESTIE LISTEN. If you feed it anything outside that input range, the function will set errno to EDOM and return zero. no crash, no drama, just EDOM and a zero. but you will know. 😭

Example, because examples are the main character:

float angle;
fixed val;

/* Sets `val' to a right binary angle (`64'). */
val = fixasin(itofix(1));
/* Sets `angle' to 0.2405. */
angle = fixtof(fixmul(fixasin(ftofix(0.238)), fixtorad_r));
/* This will trigger the assert. */
val = fixasin(ftofix(-1.09));
ASSERT(!errno);

see that last bit? yeah. that ftofix(-1.09) is out of range, errno gets set, and the ASSERT is going off. 💀 don't be that girl.

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🌈 RETURN VALUE 🌈

It returns the inverse sine of a fixed point value, measured as a fixed point binary format angle ✨ — or zero if the input was out of the range (you know, the EDOM situation we just talked about).

And ngl, this part is iconic: all return values of this function will be in the range -64 to 64. every single one. no cap. 👑

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🦋 SEE ALSO 🦋

so… there's literally nothing listed here. no cross references, no friends, no links. it's giving solo era 💅 this section is just standing there in the manual being mysterious. 🙈

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and that's the whole page, bestie 🫶 this one's from the Allegro manual, version 4.4.3, and the page is fixasin(3). no date stamped on it either, which is lowkey iconic of it ✨ go forth and only ever pass it values between -1 and 1 💖🧚