std::fmod,s...f,std::fmodl(3)

💖 std::fmod, std::fmodf, std::fmodl — C++ Standard Library 💖

manual page · section (3) · bestie, this is the whole glow-up ✨

🌸 NAME 🌸

std::fmod,std::fmodf,std::fmodl — std::fmod,std::fmodf,std::fmodl

✨ Synopsis ✨

okay so first, the receipts: this lives in <cmath>, and here’s the whole signature lineup, no cap 👑

Defined in header <cmath>

float       fmod ( float x, float y );

double      fmod ( double x, double y );                   (until C++23)

long double fmod ( long double x, long double y );
constexpr /* floating-point-type */

            fmod ( /* floating-point-type */ x,            (since C++23)
                                                       (1)
                   /* floating-point-type */ y );
float       fmodf( float x, float y );                 (2) (since C++11)
                                                               (constexpr since C++23)
long double fmodl( long double x, long double y );     (3) (since C++11)
                                                               (constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer >                              (A) (constexpr since C++23)
double      fmod ( Integer x, Integer y );

1-3) Computes the floating-point remainder of the division operation x / y.

The library provides overloads of std::fmod for all cv-unqualified floating-point types as the type of the parameters. (since C++23)

A) Additional overloads are provided for all integer types, which are treated as double. (since C++11)

The floating-point remainder of the division operation x / y calculated by this function is exactly the value x - rem * y, where rem is x / y with its fractional part truncated.

The returned value has the same sign as x and is less than y in magnitude. 🎀

🫶 Parameters 🫶

• x, y — floating-point or integer values

💖 Return value 💖

If successful, returns the floating-point remainder of the division x / y as defined above.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

🚨 Error handling 🚨

Errors are reported as specified in math_errhandling.

Domain error may occur if y is zero.

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

• If x is ±0 and y is not zero, ±0 is returned.
• If x is ±∞ and y is not NaN, NaN is returned and FE_INVALID is raised.
• If y is ±0 and x is not NaN, NaN is returned and FE_INVALID is raised.
• If y is ±∞ and x is finite, x is returned.
• If either argument is NaN, NaN is returned.

🧠 Notes 🧠

POSIX requires that a domain error occurs if x is infinite or y is zero.

std::fmod, but not std::remainder is useful for doing silent wrapping of floating-point types to unsigned integer types: (0.0 <= (y = std::fmod(std::rint(x), 65536.0)) ? y : 65536.0 + y) is in the range [-0.0, 65535.0], which corresponds to unsigned short, but std::remainder(std::rint(x), 65536.0 is in the range [-32767.0, +32768.0], which is outside of the range of signed short.

The double version of std::fmod behaves as if implemented as follows:

double fmod(double x, double y)
{
#pragma STDC FENV_ACCESS ON
    double result = std::remainder(std::fabs(x), y = std::fabs(y));
    if (std::signbit(result))
        result += y;
    return std::copysign(result, x);
}

The expression x - std::trunc(x / y) * y may not equal std::fmod(x, y), when the rounding of x / y to initialize the argument of std::trunc loses too much precision (example: x = 30.508474576271183309, y = 6.1016949152542370172).

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

• If num1 or num2 has type long double, then std::fmod(num1, num2) has the same effect as std::fmod(static_cast<long double>(num1), static_cast<long double>(num2)).
• Otherwise, if num1 and/or num2 has type double or an integer type, then std::fmod(num1, num2) has the same effect as std::fmod(static_cast<double>(num1), static_cast<double>(num2)). (until C++23)
• Otherwise, if num1 or num2 has type float, then std::fmod(num1, num2) has the same effect as std::fmod(static_cast<float>(num1), static_cast<float>(num2)).

If num1 and num2 have arithmetic types, then std::fmod(num1, num2) has the same effect as std::fmod(static_cast</* common-floating-point-type */>(num1), static_cast</* common-floating-point-type */>(num2)), where /* common-floating-point-type */ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double. (since C++23)

If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.

🌈 Example 🌈

Run this code, bestie 🫶

// Run this code

#include <cfenv>
#include <cmath>
#include <iostream>
// #pragma STDC FENV_ACCESS ON

int main()
{
    std::cout << "fmod(+5.1, +3.0) = " << std::fmod(5.1, 3) << '\n'
              << "fmod(-5.1, +3.0) = " << std::fmod(-5.1, 3) << '\n'
              << "fmod(+5.1, -3.0) = " << std::fmod(5.1, -3) << '\n'
              << "fmod(-5.1, -3.0) = " << std::fmod(-5.1, -3) << '\n';

    // special values
    std::cout << "fmod(+0.0, 1.0) = " << std::fmod(0, 1) << '\n'
              << "fmod(-0.0, 1.0) = " << std::fmod(-0.0, 1) << '\n'
              << "fmod(5.1, Inf) = " << std::fmod(5.1, INFINITY) << '\n';

    // error handling
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "fmod(+5.1, 0) = " << std::fmod(5.1, 0) << '\n';
    if (std::fetestexcept(FE_INVALID))
        std::cout << "    FE_INVALID raised\n";
}

Possible output:

fmod(+5.1, +3.0) = 2.1
fmod(-5.1, +3.0) = -2.1
fmod(+5.1, -3.0) = 2.1
fmod(-5.1, -3.0) = -2.1
fmod(+0.0, 1.0) = 0
fmod(-0.0, 1.0) = -0
fmod(5.1, Inf) = 5.1
fmod(+5.1, 0) = -nan
    FE_INVALID raised

🦋 See also 🦋

• div(int)
• ldiv, lldiv — computes quotient and remainder of integer division; lldiv is (function) (C++11).
• remainder, remainderf, remainderl — signed remainder of the division operation (function); (C++11) (C++11) (C++11).
• remquo, remquof, remquol — signed remainder as well as the three last bits of the division operation (function); (C++11) (C++11) (C++11).
• C documentation for fmod

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💖 Source receipt: cppreference.com · 2024.06.10 · page std::fmod,s...f,std::fmodl(3) — periodt, bestie, that’s the whole manual page slaying in its lane 💅✨