fmod(3) — Linux manual page

fmod(3)                 Library Functions Manual                 fmod(3)

NAME

       fmod, fmodf, fmodl - floating-point remainder function

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       double fmod(double x, double y);
       float fmodf(float x, float y);
       long double fmodl(long double x, long double y);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       fmodf(), fmodl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       These functions compute the floating-point remainder of dividing
       x by y.  The return value is x - n * y, where n is the quotient
       of x / y, rounded toward zero to an integer.

       To obtain the modulus, more specifically, the Least Positive
       Residue, you will need to adjust the result from fmod like so:

           z = fmod(x, y);
           if (z < 0)
                z += y;

       An alternate way to express this is with fmod(fmod(x, y) + y, y),
       but the second fmod() usually costs way more than the one branch.

RETURN VALUE

       On success, these functions return the value x - n*y, for some
       integer n, such that the returned value has the same sign as x
       and a magnitude less than the magnitude of y.

       If x or y is a NaN, a NaN is returned.

       If x is an infinity, a domain error occurs, and a NaN is
       returned.

       If y is zero, a domain error occurs, and a NaN is returned.

       If x is +0 (-0), and y is not zero, +0 (-0) is returned.

ERRORS

       See math_error(7) for information on how to determine whether an
       error has occurred when calling these functions.

       The following errors can occur:

       Domain error: x is an infinity
              errno is set to EDOM (but see BUGS).  An invalid floating-
              point exception (FE_INVALID) is raised.

       Domain error: y is zero
              errno is set to EDOM.  An invalid floating-point exception
              (FE_INVALID) is raised.

ATTRIBUTES

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌─────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                           │ Attribute     │ Value   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │ fmod(), fmodf(), fmodl()            │ Thread safety │ MT-Safe │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS

       Before glibc 2.10, the glibc implementation did not set errno to
       EDOM when a domain error occurred for an infinite x.

EXAMPLES

       The call fmod(372, 360) returns 348.

       The call fmod(-372, 360) returns -12.

       The call fmod(-372, -360) also returns -12.

SEE ALSO

       remainder(3)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                        fmod(3)

Pages that refer to this page: remainder(3), remquo(3)

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