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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> 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((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 .