fimf-accuracy-bits, Qimf-accuracy-bits
Defines the relative error for math
library function results, including division and square root.
This content is specific to C++; it does not apply to
DPC++
.Syntax
Linux:
-fimf-accuracy-bits
=
bits
[
:
funclist
]
Windows:
/Qimf-accuracy-bits
:
bits
[
:
funclist
]
Arguments
- bits
- Is a positive, floating-point number indicating the number of correct bits the compiler should use.The format for the number is [digits] [.digits] [ { e | E }[sign]digits].
- funclist
- Is an optional list of one or more math library functions to which the attribute should be applied. If you specify more than one function, they must be separated with commas.Precision-specific variants like sin and sinf are considered different functions, so you would need to use-fimf-accuracy-bits=23:sin,sinf(or/Qimf-accuracy-bits:23:sin,sinf) to specify the relative error for both the single-precision and double-precision sine functions.You also can specify the symbol /f to denote single-precision divides, symbol / to denote double-precision divides, symbol /l to denote extended-precision divides, and symbol /q to denote quad-precision divides. For example you can specify-fimf-accuracy-bits=10.0:/for/Qimf-accuracy-bits:10.0:/f.
Default
- -fimf-precision=medium or /Qimf-precision:medium
- The compiler uses medium precision when calling math library functions. Note that other options can affect precision; see below for details.
Description
This option defines the relative error, measured by the
number of correct bits, for math library function results.
The following formula is
used to convert bits into ulps: ulps = 2
p-1-bits
, where p is the
number of the target format mantissa bits (24, 53, and 64 for single, double,
and long double, respectively).
This option can affect run-time performance and the
accuracy of results.
If you need to define the accuracy for a math function of
a certain precision, specify the function name of the precision that you need.
For example, if you want double precision, you can specify :sin; if you want
single precision, you can specify :sinf, as in the following:
- -fimf-accuracy-bits=23:sinf,cosf,logfor/Qimf-accuracy-bits:23:sinf,cosf,logf
- -fimf-accuracy-bits=52:sqrt,/,truncor/Qimf-accuracy-bits:52:sqrt,/,trunc
- -fimf-accuracy-bits=10:powfor/Qimf-accuracy-bits:10:powf
If you do not specify any function names, then the
setting applies to all functions (and to all precisions). However, as soon as
you specify an individual function name, the setting applies only to the
function of corresponding precision. So, for example, sinf applies only to the
single-precision sine function, sin applies only to the double-precision sine
function, sinl applies only to the extended-precision sine function, etc.
There are three options you can use to express the
maximum relative error. They are as follows:
- -fimf-precision(Linux*) or/Qimf-precision(Windows*)
- -fimf-max-error(Linux*) or/Qimf-max-error(Windows*)
- -fimf-accuracy-bits(Linux) or/Qimf-accuracy-bits(Windows)
If more than one of these options are specified, the default value for the
maximum relative error is determined by the last one specified on the command
line.
If none of the above options are specified, the default values for the
maximum relative error are determined by the setting of the following options:
- -fp-model(Linux) or/fp(Windows)
Many routines in libraries LIBM (Math Library) and SVML (Short Vector Math
Library) are more highly optimized for Intel® microprocessors than for
non-Intel microprocessors.
Product and Performance Information
|
|---|
Performance varies by use, configuration and other factors. Learn more at
www.Intel.com/PerformanceIndex.
Notice revision #20201201
|
IDE Equivalent
None
Alternate Options
None