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<tgmath.h>(P)              POSIX Programmer's Manual             <tgmath.h>(P)

NAME
       tgmath.h - type-generic macros

SYNOPSIS
       #include <tgmath.h>

DESCRIPTION
       The  <tgmath.h>  header  shall  include  the headers <math.h> and <com-
       plex.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(),  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>   <complex.h>   Type-Generic
                        Function   Function      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-pre-
       fixed  counterpart  in  the <complex.h> header, 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()         scalbn()
                 erfc()       hypot()    lrint()        scalbln()
                 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  unde-
       fined 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  corre-
       sponding  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 fol-
       lowing 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((  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 IEEE Std 1003.1-2001 specifies only for real  arguments
       with the ability to invoke the complex functions.

       IEEE Std 1003.1-2001  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 <com-
       plex.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
       IEEE Std 1003.1-2001, cabs(), fabs(), modf()

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 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 .

IEEE/The Open Group                  2003                        <tgmath.h>(P)

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