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UXTB, UXTH, UXTW

Unsigned byte / halfword / word extend (predicated).

Zero-extend the least-significant sub-element of each active element of the source vector, and place the results in the corresponding elements of the destination vector. Inactive elements in the destination vector register remain unmodified.

It has encodings from 3 classes: Byte , Halfword and Word

Byte

313029282726252423222120191817161514131211109876543210
00000100size010001101PgZnZd

Byte

UXTB <Zd>.<T>, <Pg>/M, <Zn>.<T>

if !HaveSVE() then UNDEFINED;
if size == '00' then UNDEFINED;
integer esize = 8 << UInt(size);
integer s_esize = 8;
integer g = UInt(Pg);
integer n = UInt(Zn);
integer d = UInt(Zd);
boolean unsigned = TRUE;

Halfword

313029282726252423222120191817161514131211109876543210
00000100size010011101PgZnZd

Halfword

UXTH <Zd>.<T>, <Pg>/M, <Zn>.<T>

if !HaveSVE() then UNDEFINED;
if size != '1x' then UNDEFINED;
integer esize = 8 << UInt(size);
integer s_esize = 16;
integer g = UInt(Pg);
integer n = UInt(Zn);
integer d = UInt(Zd);
boolean unsigned = TRUE;

Word

313029282726252423222120191817161514131211109876543210
00000100size010101101PgZnZd

Word

UXTW <Zd>.D, <Pg>/M, <Zn>.D

if !HaveSVE() then UNDEFINED;
if size != '11' then UNDEFINED;
integer esize = 8 << UInt(size);
integer s_esize = 32;
integer g = UInt(Pg);
integer n = UInt(Zn);
integer d = UInt(Zd);
boolean unsigned = TRUE;

Assembler Symbols

<Zd>

Is the name of the destination scalable vector register, encoded in the "Zd" field.

<T> For the byte variant: is the size specifier, encoded in size:
size <T>
00 RESERVED
01 H
10 S
11 D
For the halfword variant: is the size specifier, encoded in size<0>:
size<0> <T>
0 S
1 D
<Pg>

Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Zn>

Is the name of the source scalable vector register, encoded in the "Zn" field.

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(VL) operand  = Z[n];
bits(VL) result = Z[d];

for e = 0 to elements-1
    bits(esize) element = Elem[operand, e, esize];
    if ElemP[mask, e, esize] == '1' then
        Elem[result, e, esize] = Extend(element<s_esize-1:0>, esize, unsigned);

Z[d] = result;

Operational information

If PSTATE.DIT is 1:

  • The execution time of this instruction is independent of:
    • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
    • The values of the NZCV flags.
  • The response of this instruction to asynchronous exceptions does not vary based on:
    • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
    • The values of the NZCV flags.

This instruction might be immediately preceded in program order by a MOVPRFX instruction that conforms to all of the following requirements, otherwise the behavior of either or both instructions is unpredictable:

  • The MOVPRFX instruction must specify the same destination register as this instruction.
  • The destination register must not refer to architectural register state referenced by any other source operand register of this instruction.
The MOVPRFX instructions that can be used with this instruction are as follows:
  • An unpredicated MOVPRFX instruction.
  • A predicated MOVPRFX instruction using the same governing predicate register and source element size as this instruction.
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