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21.56 QN, DN, and SN

The QN, DN, and SN directives define names for Advanced SIMD and floating-point registers.

Syntax

name directive expr{.type}{[x]}

where:

directive

is QN, DN,or SN.

name

is the name to be assigned to the extension register. name cannotbe the same as any of the predefined names.

expr

Can be:

  • An expression that evaluates to a number in the range:

    • 0-15 if you are using QN in A32/T32 Advanced SIMD code.

    • 0-31 otherwise.

  • A predefined register name, or a register name that has already been defined in a previous directive.

type

is any Advanced SIMD or floating-point datatype.

[x]

is only available for Advanced SIMD code. [x] is a scalar index into a register.

type and [x] are Extendednotation.

Usage

Use QN, DN,or SN to allocate convenient names to extensionregisters, to help you to remember what you use each one for.

The QN directive defines a name for a specified 128-bit extension register.

The DN directive defines a name for a specified 64-bit extension register.

The SN directive defines a name for a specified single-precision floating-point register.

Note

Avoid conflicting uses of the same register under different names.

You cannot specify a vector length in a DN or SN directive.

Examples

energy  DN  6   ; defines energy as a symbol for                ; floating-point double-precision register 6mass    SN  16  ; defines mass as a symbol for                ; floating-point single-precision register 16

Extended notation examples

varA    DN      d1.U16varB    DN      d2.U16varC    DN      d3.U16        VADD    varA,varB,varC       ; VADD.U16 d1,d2,d3index   DN      d4.U16[0]result  QN      q5.I32        VMULL   result,varA,index    ; VMULL.U16 q5,d1,d4[0]
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