fixed.Quantizer

Quantize fixed-point numbers

collapse all in page

Syntax

q = fixed.Quantizer
q = fixed.Quantizer(nt,rm,oa)
q = fixed.Quantizer(s,wl,fl,rm,oa)
q = fixed.Quantizer(Name,Value)

Description

q = fixed.Quantizer creates a quantizer q that quantizes fixed-point (fi) numbers using default fixed-point settings.

q = fixed.Quantizer(nt,rm,oa) uses the numerictype (nt) object information and the RoundingMethod (rm) and OverflowAction (oa) properties.

The numerictype, rounding method, and overflow action apply only during the quantization. The resulting, quantized q does not have any fimath attached to it.

q = fixed.Quantizer(s,wl,fl,rm,oa) uses the Signed (s), WordLength (wl), FractionLength (fl), RoundingMethod (rm), and OverflowAction (oa) properties.

q = fixed.Quantizer(Name,Value) creates a quantizer with the property options specified by one or more Name,Value pair arguments. You separate pairs of Name,Value arguments with commas. Name is the argument name, and Value is the corresponding value. Name must appear inside single quotes (''). You can specify several name-value pair arguments in any order as Name1,Value1,…,NameN,ValueN.

Input Arguments

nt

Binary-point, scaled numerictype object or slope-bias scaled, fixed-point numerictype object. If your fixed.Quantizer uses a numerictype object that has either a Signedness of Auto or unspecified Scaling, an error occurs.

rm

Rounding method to apply to the output data. Valid rounding methods are: Ceiling, Convergent, Floor, Nearest, Round, and Zero. The associated property name is RoundingMethod.

Default: Floor

oa

Overflow action to take in case of data overflow. Valid overflow actions are Saturate and Wrap. The associated property name is OverflowAction.

Default: Wrap

s

Logical value, true or false, indicating whether the output is signed or unsigned, respectively. The associated property name is Signed.

Default: true

wl

Word length (number of bits) of the output data. The associated property name is WordLength.

Default: 16

fl

Fraction length of the output data. The associated property name is FractionLength.

Default: 15

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Bias

The bias is part of the numerical representation used to interpret a fixed-point number. Along with the slope, the bias forms the scaling of the number.

Default: 0

FixedExponent

Fixed-point exponent associated with the object. The exponent is part of the numerical representation used to express a fixed-point number.

The exponent of a fixed-point number is equal to the negative of the fraction length. FixedExponent must be an integer.

Default: -15

FractionLength

Fraction length of the stored integer value of the object, in bits. The fraction length can be any integer value.

This property automatically defaults to the best precision possible based on the value of the word length and the real-world value of the fi object.

Default: 15

OverflowAction

Action to take in case of data overflow. Valid overflow actions are Saturate and Wrap. .

Default: Wrap

RoundingMethod

Rounding method to apply to the output data. Valid rounding methods are: Ceiling, Convergent, Floor, Nearest, Round, and Zero.

Default: Floor

Signed

Whether the object is signed. The possible values of this property are:

  • 1 — signed

  • 0 — unsigned

  • true — signed

  • false — unsigned

Note

Although the Signed property is still supported, the Signedness property always appears in the numerictype object display. If you choose to change or set the signedness of your numerictype object using the Signed property, MATLAB® updates the corresponding value of the Signedness property.

Default: true

Signedness

Whether the object is signed, unsigned, or has an unspecified sign. The possible values of this property are:

  • Signed — signed

  • Unsigned — unsigned

Default: Signed

Slope

Slope associated with the object. The slope is part of the numerical representation used to express a fixed-point number. Along with the bias, the slope forms the scaling of a fixed-point number.

Default: 2^-15

SlopeAdjustmentFactor

Slope adjustment associated with the object. The slope adjustment is equivalent to the fractional slope of a fixed-point number. The fractional slope is part of the numerical representation used to express a fixed-point number.

SlopeAdjustmentFactor must be greater than or equal to 1 and less than 2.

Default: 1

WordLength

Word length of the stored integer value of the object, in bits. The word length can be any positive integer value.

Default: 16

Output Arguments

q

Quantizer that quantizes fi input numbers

Examples

Use fixed.Quantizer to reduce the word length that results from adding two fixed-point numbers.

q = fixed.Quantizer;
x1 = fi(0.1,1,16,15);
x2 = fi(0.8,1,16,15);
y  = quantize(q,x1+x2);

Use fixed.Quantizer object to change a binary point scaled fixed-point fi to a slope-bias scaled fixed-point fi 

qsb = fixed.Quantizer(numerictype(1,7,1.6,0.2),...
  'Round','Saturate');
ysb = quantize(qsb,fi(pi,1,16,13));

More About

collapse all

Fixed-point numbers

Fixed-point numbers can be represented as

real-world value=(slope×stored integer)+bias

where the slope can be expressed as

slope=fractional slope×2fixed exponent

Tips

  • Use y = quantize(q,x) to quantize input array x using the fixed-point settings of quantizer q. x can be any fixed-point number fi, except a Boolean value. If x is a scaled double, the x and y data will be the same, but y will have fixed-point settings. If x is a double or single then y = x. This functionality lets you share the same code for both floating-point data types and fi objects when quantizers are present.

  • Use n = numerictype(q) to get a numerictype for the current settings of quantizer q.

  • Use clone(q) to create a quantizer object with the same property values as q.

  • If you use a fixed.quantizer in code generation, note that it is a handle object and must be declared as persistent.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

See Also

| |

Topics

Introduced in R2011b

Fixed-Point Designer Documentation

Support