fp-contract.md

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fp_contract | Microsoft Docs		11/04/2016			cpp-tools		article	vc-pragma.fp_contract fp_contract_CPP	C++	pragmas, fp_contract fp_contract pragma	15b97338-6680-4287-ba2a-2dccc5b2ccf5	12	corob-msft	corob	ghogen	cs-cz de-de es-es fr-fr it-it ja-jp ko-kr pl-pl pt-br ru-ru tr-tr zh-cn zh-tw

fp_contract

Determines whether floating-point contraction will take place.

Syntax

#pragma fp_contract [ON | OFF]  

Remarks

By default, fp_contract is ON.

For more information on floating-point behavior, see /fp (Specify Floating-Point Behavior).

Other floating-point pragmas include:

• fenv_access

• float_control

Example

The code generated from this sample does not use the Fused Multiply Add (fma) instruction on Itanium processors. If you comment out #pragma fp_contract (off), the generated code will use the fma instruction.

// pragma_directive_fp_contract.cpp  
// compile with: /O2  
#include <stdio.h>  
#include <float.h>  
  
#pragma fp_contract (off)   
  
int main() {  
   double z, b, t;  
  
   for (int i = 0; i < 10; i++) {  
      b = i * 5.5;  
      t = i * 56.025;  
      _set_controlfp(_PC_24, _MCW_PC);  
  
      z = t * i + b;  
      printf_s ("out=%.15e\n", z);  
   }  
}  

out=0.000000000000000e+000  
out=6.152500152587891e+001  
out=2.351000061035156e+002  
out=5.207249755859375e+002  
out=9.184000244140625e+002  
out=1.428125000000000e+003  
out=2.049899902343750e+003  
out=2.783724853515625e+003  
out=3.629600097656250e+003  
out=4.587524902343750e+003  

See Also

Pragma Directives and the __Pragma Keyword