tgmath.h(3)                POSIX Programmer's Manual               tgmath.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       tgmath.h -- type-generic macros

SYNOPSIS
       #include <tgmath.h>

DESCRIPTION
       The functionality described on this reference page is aligned with the
       ISO C standard. Any conflict between the requirements described here
       and the ISO C standard is unintentional. This volume of POSIX.1-2017
       defers to the ISO C standard.

       The <tgmath.h> header shall include the headers <math.h> and
       <complex.h> and shall define several type-generic macros.

       Of the functions contained within the <math.h> and <complex.h> headers
       without an _f (float) or _l (long double) suffix, several have one or
       more parameters whose corresponding real type is double.  For each such
       function, except modf(), j0(), j1(), jn(), y0(), y1(), and yn(), there
       shall be a corresponding type-generic macro. The parameters whose
       corresponding real type is double in the function synopsis are generic
       parameters. Use of the macro invokes a function whose corresponding
       real type and type domain are determined by the arguments for the
       generic parameters.

       Use of the macro invokes a function whose generic parameters have the
       corresponding real type determined as follows:

        *  First, if any argument for generic parameters has type long double,
           the type determined is long double.

        *  Otherwise, if any argument for generic parameters has type double
           or is of integer type, the type determined is double.

        *  Otherwise, the type determined is float.

       For each unsuffixed function in the <math.h> header for which there is
       a function in the <complex.h> header with the same name except for a _c
       prefix, the corresponding type-generic macro (for both functions) has
       the same name as the function in the <math.h> header. The corresponding
       type-generic macro for fabs() and cabs() is fabs().

           +------------------+----------------------+--------------------+
           |<math.h> Function | <complex.h> Function | Type-Generic Macro |
           +------------------+----------------------+--------------------+
           |acos()            | cacos()              | acos()             |
           |asin()            | casin()              | asin()             |
           |atan()            | catan()              | atan()             |
           |acosh()           | cacosh()             | acosh()            |
           |asinh()           | casinh()             | asinh()            |
           |atanh()           | catanh()             | atanh()            |
           |cos()             | ccos()               | cos()              |
           |sin()             | csin()               | sin()              |
           |tan()             | ctan()               | tan()              |
           |cosh()            | ccosh()              | cosh()             |
           |sinh()            | csinh()              | sinh()             |
           |tanh()            | ctanh()              | tanh()             |
           |exp()             | cexp()               | exp()              |
           |log()             | clog()               | log()              |
           |pow()             | cpow()               | pow()              |
           |sqrt()            | csqrt()              | sqrt()             |
           |fabs()            | cabs()               | fabs()             |
           +------------------+----------------------+--------------------+
       If at least one argument for a generic parameter is complex, then use
       of the macro invokes a complex function; otherwise, use of the macro
       invokes a real function.

       For each unsuffixed function in the <math.h> header without a _c-
       prefixed counterpart in the <complex.h> header, except for modf(),
       j0(), j1(), jn(), y0(), y1(), and yn(), the corresponding type-generic
       macro has the same name as the function.  These type-generic macros
       are:


              atan2()      fma()      llround()      remainder()
              cbrt()       fmax()     log10()        remquo()
              ceil()       fmin()     log1p()        rint()
              copysign()   fmod()     log2()         round()
              erf()        frexp()    logb()         scalbln()
              erfc()       hypot()    lrint()        scalbn()
              exp2()       ilogb()    lround()       tgamma()
              expm1()      ldexp()    nearbyint()    trunc()
              fdim()       lgamma()   nextafter()
              floor()      llrint()   nexttoward()

       If all arguments for generic parameters are real, then use of the macro
       invokes a real function; otherwise, use of the macro results in
       undefined behavior.

       For each unsuffixed function in the <complex.h> header that is not a _c-
       prefixed counterpart to a function in the <math.h> header, the
       corresponding type-generic macro has the same name as the function.
       These type-generic macros are:

              carg() cimag() conj() cproj() creal()

       Use of the macro with any real or complex argument invokes a complex
       function.

       The following sections are informative.

APPLICATION USAGE
       With the declarations:


           #include <tgmath.h>
           int n;
           float f;
           double d;
           long double ld;
           float complex fc;
           double complex dc;
           long double complex ldc;

       functions invoked by use of type-generic macros are shown in the
       following table:

                 +-----------------+-------------------------------+
                 |     Macro       |          Use Invokes          |
                 +-----------------+-------------------------------+
                 |exp(_n)           | exp(_n), the function          |
                 |acosh(_f)         | acoshf(_f)                     |
                 |sin(_d)           | sin(_d), the function          |
                 |atan(ld)         | atanl(ld)                     |
                 |log(fc)          | clogf(fc)                     |
                 |sqrt(dc)         | csqrt(dc)                     |
                 |pow(ldc,f)       | cpowl(ldc, _f)                 |
                 |remainder(n,n)   | remainder(_n_, _n), the function |
                 |nextafter(d,f)   | nextafter(_d_, _f), the function |
                 |nexttoward(f,ld) | nexttowardf(_f_, ld)            |
                 |copysign(n,ld)   | copysignl(_n_, ld)              |
                 |ceil(fc)         | Undefined behavior            |
                 |rint(dc)         | Undefined behavior            |
                 |fmax(ldc,ld)     | Undefined behavior            |
                 |carg(_n)          | carg(_n), the function         |
                 |cproj(_f)         | cprojf(_f)                     |
                 |creal(_d)         | creal(_d), the function        |
                 |cimag(ld)        | cimagl(ld)                    |
                 |cabs(fc)         | cabsf(fc)                     |
                 |carg(dc)         | carg(dc), the function        |
                 |cproj(ldc)       | cprojl(ldc)                   |
                 +-----------------+-------------------------------+
RATIONALE
       Type-generic macros allow calling a function whose type is determined
       by the argument type, as is the case for C operators such as ''++'' and
       ''**''.  For example, with a type-generic cos() macro, the expression
       cos((ffllooaatt)_x) will have type float.  This feature enables writing more
       portably efficient code and alleviates need for awkward casting and
       suffixing in the process of porting or adjusting precision. Generic
       math functions are a widely appreciated feature of Fortran.

       The only arguments that affect the type resolution are the arguments
       corresponding to the parameters that have type double in the synopsis.
       Hence the type of a type-generic call to nexttoward(), whose second
       parameter is long double in the synopsis, is determined solely by the
       type of the first argument.

       The term ``type-generic'' was chosen over the proposed alternatives of
       intrinsic and overloading. The term is more specific than intrinsic,
       which already is widely used with a more general meaning, and reflects
       a closer match to Fortran's generic functions than to C++ overloading.

       The macros are placed in their own header in order not to silently
       break old programs that include the <math.h> header; for example, with:


           printf ("%e", sin(x))

       modf(double, double **) is excluded because no way was seen to make it
       safe without complicating the type resolution.

       The implementation might, as an extension, endow appropriate ones of
       the macros that POSIX.1-2008 specifies only for real arguments with the
       ability to invoke the complex functions.

       POSIX.1-2008 does not prescribe any particular implementation mechanism
       for generic macros. It could be implemented simply with built-in
       macros. The generic macro for sqrt(), for example, could be implemented
       with:


           #undef sqrt
           #define sqrt(x) __BUILTIN_GENERIC_sqrt(x)

       Generic macros are designed for a useful level of consistency with C++
       overloaded math functions.

       The great majority of existing C programs are expected to be unaffected
       when the <tgmath.h> header is included instead of the <math.h> or
       <complex.h> headers. Generic macros are similar to the
       ISO/IEC 9899:1999 standard library masking macros, though the semantic
       types of return values differ.

       The ability to overload on integer as well as floating types would have
       been useful for some functions; for example, copysign().  Overloading
       with different numbers of arguments would have allowed reusing names;
       for example, remainder() for remquo().  However, these facilities would
       have complicated the specification; and their natural consistent use,
       such as for a floating abs() or a two-argument atan(), would have
       introduced further inconsistencies with the ISO/IEC 9899:1999 standard
       for insufficient benefit.

       The ISO C standard in no way limits the implementation's options for
       efficiency, including inlining library functions.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <math.h>, <complex.h>

       The System Interfaces volume of POSIX.1-2017, cabs(), fabs(), modf()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          tgmath.h(3)
