Simulink®

fixptbestexp

Determine exponent that gives best precision fixed-point representation of value

Syntax

out = fixptbestexp(RealWorldValue,TotalBits,IsSigned)
out = fixptbestexp(RealWorldValue,FixPtDataType)

Description

out = fixptbestexp(RealWorldValue,TotalBits,IsSigned) determines the exponent that gives the best precision for the fixed-point representation of the real-world value specified by RealWorldValue. You specify the number of bits for the fixed-point number with TotalBits, and you specify whether the fixed-point number is signed with IsSigned. If IsSigned is 1, the number is signed. If IsSigned is 0, the number is not signed. The exponent is returned to out.

out = fixptbestexp(RealWorldValue,FixPtDataType) determines the exponent that gives the best precision based on the data type specified by FixPtDataType.

Examples

The following command returns the exponent that gives the best precision for the real-world value 4/3 using a signed, 16-bit number:

out = fixptbestexp(4/3,16,1)
out =
   -14

Alternatively, you can specify the fixed-point data type:

out = fixptbestexp(4/3,sfix(16))
out =
   -14

This value means that the maximum precision representation of 4/3 is obtained by placing 14 bits to the right of the binary point:

01.01010101010101

You would specify the precision of this representation in fixed-point blocks by setting the scaling to 2^-14 or 2^fixptbestexp(4/3,16,1).

See Also

fixptbestprec

fixpt_set_all

fixptbestprec