fma, fmaf, fmal

项目
06/05/2017

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at fma, fmaf, fmal.

Multiplies two values together, adds a third value, and then rounds the result, without losing any precision due to intermediary rounding.

Syntax

double fma(  
   double x,   
   double y,   
   double z  
);  
  
float fma(  
   float  x,   
   float  y,   
   float z  
); //C++ only  
  
long double fma(  
   long double  x,   
   long double  y,   
   long double z  
); //C++ only  
  
float fmaf(  
   float  x,   
   float  y,   
   float z  
);  
  
long double fmal(  
   long double  x,   
   long double  y,   
   long double z  
);

Parameters

[in] x
The first value to multiply.

[in] y
The second value to multiply.

[in] z
The value to add.

Return Value

Returns (x × y) + z. The return value is then rounded using the current rounding format.

Otherwise, may return one of the following values:

Issue	Return
`x` = INFINITY, `y` = 0 or `x` = 0, `y` = INFINITY	NaN
`x` or `y` = exact ± INFINITY, `z` = INFINITY with the opposite sign	NaN
`x` or `y` = NaN	NaN
not (`x` = 0, `y`= indefinite) and `z` = NaN not (`x`=indefinite, `y`=0) and `z` = NaN	NaN
Overflow range error	±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL
Underflow range error	correct value, after rounding.

Errors are reported as specified in _matherr.

Remarks

Because C++ allows overloading, you can call overloads of fma that take and return float and long double types. In a C program, fma always takes and returns a double.

This function computes the value as though it were taken to infinite precision, and then rounds the final result.

Requirements

Function	C header	C++ header
`fma`, `fmaf`, `fmal`	<math.h>	<cmath>

For additional compatibility information, see Compatibility.

通过