PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

tgmath.h(0P)              POSIX Programmer's Manual             tgmath.h(0P)

PROLOG         top

       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         top

       tgmath.h — type-generic macros

SYNOPSIS         top

       #include <tgmath.h>

DESCRIPTION         top

       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> 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         top

       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         top

       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         top

       None.

SEE ALSO         top

       math.h(0p), complex.h(0p)

       The System Interfaces volume of POSIX.1‐2008, cabs(3p), fabs(3p),
       modf(3p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                        tgmath.h(0P)