fma, fmaf, fmal

Article
06/05/2017

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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.