Expressions that involve special values (NaN, +infinity, -infinity, -0.0) are processed according to IEEE-754 specifications. The compiler doesn't perform algebraic transformations on floating-point expressions, such as reassociation or distribution, unless it can guarantee the transformation produces a bitwise identical result. Typecasts can be used to explicitly round intermediate computations. Intermediate computations may be performed at machine precision. The compiler rounds to source code precision at four specific points during expression evaluation: at assignments, typecasts, when floating-point arguments get passed to a function call, and when a function call returns a floating-point value. Under /fp:precise, the compiler preserves the source expression ordering and rounding properties of floating-point code when it generates and optimizes object code for the target machine. fp:preciseīy default, the compiler uses /fp:precise behavior. The /fp:contract option is new in Visual Studio 2022. The /fp:contract option isn't compatible with /fp:strict. The speed comes at a cost of bitwise exact results, and an inability to examine the intermediate value.īy default, the /fp:fast option enables /fp:contract. Since it's implemented as a single instruction, it can be faster than separate instructions. FMA, defined as a basic operation by IEEE-754, doesn't round the intermediate product before the addition, so the result can differ from separate multiplication and addition operations. A contraction is a machine instruction that combines floating-point operations, such as Fused-Multiply-Add (FMA). The /fp:contract option allows the compiler to generate floating-point contractions when you specify the /fp:precise and /fp:except options.
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