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tgmath.h(0P) POSIX Programmer's Manual tgmath.h(0P)
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.
tgmath.h — type-generic macros
#include <tgmath.h>
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.
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) │
└─────────────────┴───────────────────────────────┘
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.
None.
math.h(0p), complex.h(0p)
The System Interfaces volume of POSIX.1‐2008, cabs(3p), fabs(3p),
modf(3p)
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)
Pages that refer to this page: nextafter(3p)