Originální popis anglicky:
tgmath.h - type-generic macros
Návod, kniha: POSIX Programmer's Manual
#include <tgmath.h>
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() cbrt() ceil() copysign()
erf() erfc() exp2() expm1() fdim()
floor() |
fma() fmax() fmin() fmod() frexp()
hypot() ilogb() ldexp() lgamma()
llrint() |
llround() log10() log1p() log2()
logb() lrint() lround() nearbyint()
nextafter() nexttoward() |
remainder() remquo() rint() round()
scalbn() scalbln() tgamma() trunc()
|
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:
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.
None.
<math.h> ,
<complex.h> , the System Interfaces volume
of IEEE Std 1003.1-2001,
cabs(),
fabs(),
modf()
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
.