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Fixed-Point Numbers in Simulink

Simulink® data type names must be valid MATLAB® identifiers with less than 128 characters. The data type name provides information about container type, number encoding, and scaling.

You can represent a fixed-point number using the fixed-point scaling equation

VV~=SQ+B,

where

  • V is the real-world value.

  • V~ is the approximate real-world value.

  • S = F2E is the slope.

  • F is the slope adjustment factor, where F is a value in the range [1.0, 2.0).

  • E is the fixed power-of-two exponent.

  • Q is the stored integer.

  • B is the bias.

Fixed-Point Data Type and Scaling Notation

The following table provides a key for various symbols that appear in Simulink products to indicate the data type and scaling of a fixed-point value.

Symbol

Description

Example

Container Type

ufix

Unsigned fixed-point data type

ufix8 is an 8-bit unsigned fixed-point data type

sfix

Signed fixed-point data type

sfix128 is a 128-bit signed fixed-point data type

fltu

Scaled Doubles override of an unsigned fixed-point data type (ufix)

fltu32 is a scaled doubles override of ufix32

flts

Scaled Doubles override of a signed fixed-point data type (sfix)

flts64 is a scaled doubles override of sfix64

Number Encoding

e

10^

125e8 equals 125*(10^(8))

n

Negative

n31 equals -31

p

Decimal point

1p5 equals 1.5

p2 equals 0.2

Scaling Encoding

S

Slope

ufix16_S5_B7 is a 16-bit unsigned fixed-point data type with Slope of 5 and Bias of 7

B

Bias

ufix16_S5_B7 is a 16-bit unsigned fixed-point data type with Slope of 5 and Bias of 7

E

Fixed exponent (2^)

A negative fixed exponent describes the fraction length

sfix32_En31 is a 32-bit signed fixed-point data type with a fraction length of 31

F

Slope adjustment factor

ufix16_F1p5_En50 is a 16-bit unsigned fixed-point data type with a SlopeAdjustmentFactor of 1.5 and a FixedExponent of -50

C, c, D, or d

Compressed encoding for Bias

Note

If you pass this symbol to the slDataTypeAndScale function, it returns a valid fixdt data type.

No example available. For backwards compatibility only.

To identify and replace calls to slDataTypeAndScale, use the Check for calls to slDataTypeAndScale Model Advisor check.

T or t

Compressed encoding for Slope

Note

If you pass this symbol to the slDataTypeAndScale, it returns a valid fixdt data type.

No example available. For backwards compatibility only.

To identify and replace calls to slDataTypeAndScale, use the Check for calls to slDataTypeAndScale Model Advisor check.

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