COSPI(3)

💖 NAME 💖

okay bestie, welcome to COSPI(3) from the Library Functions Manual — the half–cycle cosine functions are here and they are iconic 💅

cospi, cospif, cospil — half–cycle cosine functions. That's the whole NAME vibe: these are the half–cycle cosine girlies.

📚 LIBRARY 📚

Math Library (libm, -lm). libm girlies, no cap.

✨ SYNOPSIS ✨

Here's the exact include + signatures, bestie — copy-paste energy only:

#include <math.h>

double
cospi(double x);

float
cospif(float x);

long double
cospil(long double x);

🌸 DESCRIPTION 🌸

Okay so the cospi(), cospif(), and cospil() functions compute the cosine of π × x. and measure angles in half-cycles. Half-cycles, not full cycles — iykyk.

🎀 RETURN VALUES 🎀

The cospi(), cospif(), and cospil() functions return cos(π × x). If |x| ≥ 2^(p - 1) where p is the floating–point precision of x, then the returned value is 1 and it has no significance. No significance means no significance, bestie — don't build your whole personality on that result.

🦋 SPECIAL VALUES 🦋

vibe check on the special values:

• cospi(±0) returns 1.
• cospi(±n/2) returns 0 for positive integers n.
• cospi(n) returns 1 for even integers n.
• cospi(n) returns -1 for odd integers n.
• cospi(±∞) returns an NaN and raises an FE_INVALID exception.
• cospi(NaN) returns an NaN and raises an FE_INVALID exception.

🔗 SEE ALSO 🔗

Go read these too, iykyk:

• cos(3)
• fenv(3)
• math(3)
• sin(3)
• sinpi(3)
• tan(3)
• tanpi(3)

👑 AUTHORS 👑

The half–cycle trignometric functions were written by Steven G. Kargl <kargl@FreeBSD.org>. Respect the author, bestie.

🌈 STANDARDS 🌈

The standards sentence is literally this, weird commas and all:

These functions conform to , to ISO/IEC TS 18661-4, "Information technology — Programming languages, their environments, and system software interfaces — Floating–point extensions for C" — Part 4: Supplementary functions, and to .

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mwah 💋 — this page is a Debian joint dated November 16, 2025, and it's the COSPI(3) manual page. byeee 🫶