Originální popis anglicky:
fma, fmaf, fmal - floating-point multiply-add
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
double fma(double
x, double
y, double z);
float fmaf(float
x, float
y, float z);
long double fmal(long double
x, long double
y, long double z);
These functions shall compute (
x *
y) +
z, rounded as one
ternary operation: they shall compute the value (as if) to infinite precision
and round once to the result format, according to the rounding mode
characterized by the value of FLT_ROUNDS.
An application wishing to check for error situations should set
errno to
zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if
errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an error has occurred.
Upon successful completion, these functions shall return (
x *
y) +
z, rounded as one ternary
operation.
If
x or
y are NaN, a NaN shall be returned.
If
x multiplied by
y is an exact infinity and
z is also an
infinity but with the opposite sign, a domain error shall occur, and either a
NaN (if supported), or an implementation-defined value shall be returned.
If one of
x and
y is infinite, the other is zero, and
z is
not a NaN, a domain error shall occur, and either a NaN (if supported), or an
implementation-defined value shall be returned.
If one of
x and
y is infinite, the other is zero, and
z is
a NaN, a NaN shall be returned and a domain error may occur.
If
x*
y is not 0*Inf nor Inf*0 and
z is a NaN, a NaN shall
be returned.
These functions shall fail if:
- Domain Error
- The value of x* y+ z is invalid, or
the value x* y is invalid and z is not a NaN.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [EDOM]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid
floating-point exception shall be raised.
- Range Error
- The result overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow
floating-point exception shall be raised.
These functions may fail if:
- Domain Error
- The value x* y is invalid and z is a
NaN.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [EDOM]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid
floating-point exception shall be raised.
- Range Error
- The result underflows.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow
floating-point exception shall be raised.
The following sections are informative.
None.
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.
In many cases, clever use of floating (
fused) multiply-add leads to much
improved code; but its unexpected use by the compiler can undermine carefully
written code. The FP_CONTRACT macro can be used to disallow use of floating
multiply-add; and the
fma() function guarantees its use where desired.
Many current machines provide hardware floating multiply-add instructions;
software implementation can be used for others.
None.
feclearexcept() ,
fetestexcept() , the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error
Conditions for Mathematical Functions,
<math.h>
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
.
