Controls the semantics of floating-point calculations.
IDE Equivalent
Windows: Code Generation>Floating Point Model
Code Generation>Enable Floating Point Exceptions
Code Generation> Floating Point Expression Evaluation
Linux: Floating Point > Floating Point Model
Mac OS X: Floating Point > Floating Point Model
Floating Point > Reliable Floating Point Exceptions Model
Architectures
IA-32, Intel® 64, IA-64 architectures
Syntax
Linux and Mac OS X: | -fp-model keyword |
Windows: | /fp:keyword |
Arguments
keyword |
Specifies the semantics to be used. Possible values are:
|
Default
-fp-model fast=1 |
The compiler uses more aggressive optimizations on floating-point calculations. |
Description
This option controls the semantics of floating-point calculations.
The keywords can be considered in groups:
Group A: precise, fast, strict
Group B: source, double, extended
Group C: except (or the negative form)
You can use more than one keyword. However, the following rules apply:
You cannot specify fast and except together in the same compilation. You can specify any other combination of group A, group B, and group C.
Since fast is the default, you must not specify except without a group A or group B keyword.You should specify only one keyword from group A and only one keyword from group B. If you try to specify more than one keyword from either group A or group B, the last (rightmost) one takes effect.
If you specify except more than once, the last (rightmost) one takes effect.
Option |
Description |
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-fp-model precise or /fp:precise |
Tells the compiler to strictly adhere to value-safe optimizations when implementing floating-point calculations. It disables optimizations that can change the result of floating-point calculations, which is required for strict ANSI conformance. These semantics ensure the accuracy of floating-point computations, but they may slow performance. The compiler assumes the default floating-point environment; you are not allowed to modify it. Intermediate results are computed with the precision shown in the following table, unless it is overridden by a keyword from Group B:
Floating-point exception semantics are disabled by default. To enable these semantics, you must also specify -fp-model except or /fp:except. For information on the semantics used to interpret floating-point calculations in the source code, see precise in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model fast[=1|2] or /fp:fast[=1|2] |
Tells the compiler to use more aggressive optimizations when implementing floating-point calculations. These optimizations increase speed, but may alter the accuracy of floating-point computations. Specifying fast is the same as specifying fast=1. fast=2 may produce faster and less accurate results. Floating-point exception semantics are disabled by default and they cannot be enabled because you cannot specify fast and except together in the same compilation. To enable exception semantics, you must explicitly specify another keyword (see other keyword descriptions for details). For information on the semantics used to interpret floating-point calculations in the source code, see fast in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model strict or /fp:strict |
Tells the compiler to strictly adhere to value-safe optimizations when implementing floating-point calculations and enables floating-point exception semantics. This is the strictest floating-point model. The compiler does not assume the default floating-point environment; you are allowed to modify it. Floating-point exception semantics can be disabled by explicitly specifying -fp-model no-except or /fp:except-. For information on the semantics used to interpret floating-point calculations in the source code, see strict in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model source or /fp:source |
This option causes intermediate results to be rounded to the precision defined in the source code. It also implies keyword precise unless it is overridden by a keyword from Group A. Intermediate expressions use the precision of the operand with higher precision, if any.
The compiler assumes the default floating-point environment; you are not allowed to modify it. For information on the semantics used to interpret floating-point calculations in the source code, see source in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model double or /fp:double |
This option causes intermediate results to be rounded as follows:
This option also implies keyword precise unless it is overridden by a keyword from Group A. The compiler assumes the default floating-point environment; you are not allowed to modify it. For information on the semantics used to interpret floating-point calculations in the source code, see double in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model extended or /fp:extended |
This option causes intermediate results to be rounded as follows:
This option also implies keyword precise unless it is overridden by a keyword from Group A. The compiler assumes the default floating-point environment; you are not allowed to modify it. For information on the semantics used to interpret floating-point calculations in the source code, see double in Floating-point Operations: Using the -fp-model (/fp) Option. |
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-fp-model except or /fp:except |
Tells the compiler to use floating-point exception semantics. |
Note
On Windows and Linux operating systems on IA-32 architecture, the compiler, by default, implements floating-point (FP) arithmetic using SSE2 and SSE instructions. This can cause differences in floating-point results when compared to previous x87 implementations.
Alternate Options
None
Example
For examples of how to use this option, see Floating-point Operations: Using the -fp-model (/fp) Option.