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NAME
tgmath.h - type-generic macros
SYNOPSIS
#include <tgmath.h>
DESCRIPTION
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(), 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-prefixed 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 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
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 <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 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 .