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

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.1‐2008 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> FunctionType-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:

                           ┌─────────────────┬───────────────────────────────┐
                           │     MacroUse 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((float)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.1‐2008, cabs(), fabs(), modf()

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .