(old) htmldiff from-(new)

DECB, DECD, DECH, DECW (scalar)

Decrement scalar by multiple of predicate constraint element count.

Determines the number of active elements implied by the named predicate constraint, multiplies that by an immediate in the range 1 to 16 inclusive, and then uses the result to decrement the scalar destination.

The named predicate constraint limits the number of active elements in a single predicate to:

* A fixed number (VL1 to VL256)

* The largest power of two (POW2)

* The largest multiple of three or four (MUL3 or MUL4)

* All available, implicitly a multiple of two (ALL).

Unspecified or out of range constraint encodings generate an empty predicate or zero element count rather than Undefined Instruction exception.

It has encodings from 4 classes: Byte , Doubleword , Halfword and Word

Byte

313029282726252423222120191817161514131211109876543210
000001000011imm4111001patternRdn

Byte

DECB <Xdn>{, <pattern>{, MUL #<imm>}}

if !HaveSVE() then UNDEFINED; integer esize = 8; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1;

Doubleword

313029282726252423222120191817161514131211109876543210
000001001111imm4111001patternRdn

Doubleword

DECD <Xdn>{, <pattern>{, MUL #<imm>}}

if !HaveSVE() then UNDEFINED; integer esize = 64; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1;

Halfword

313029282726252423222120191817161514131211109876543210
000001000111imm4111001patternRdn

Halfword

DECH <Xdn>{, <pattern>{, MUL #<imm>}}

if !HaveSVE() then UNDEFINED; integer esize = 16; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1;

Word

313029282726252423222120191817161514131211109876543210
000001001011imm4111001patternRdn

Word

DECW <Xdn>{, <pattern>{, MUL #<imm>}}

if !HaveSVE() then UNDEFINED; integer esize = 32; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1;

Assembler Symbols

<Xdn>

Is the 64-bit name of the source and destination general-purpose register, encoded in the "Rdn" field.

<pattern> Is the optional pattern specifier, defaulting to ALL, encoded in pattern:
pattern<pattern>
00000POW2
00001VL1
00010VL2
00011VL3
00100VL4
00101VL5
00110VL6
00111VL7
01000VL8
01001VL16
01010VL32
01011VL64
01100VL128
01101VL256
0111x#uimm5
101x1#uimm5
10110#uimm5
1x0x1#uimm5
1x010#uimm5
1xx00#uimm5
11101MUL4
11110MUL3
11111ALL
<imm>

Is the immediate multiplier, in the range 1 to 16, defaulting to 1, encoded in the "imm4" field.

Operation

CheckSVEEnabled(); integer count = DecodePredCount(pat, esize); bits(64) operand1 = X[dn]; X[dn] = operand1 - (count * imm);

Operational information

If PSTATE.DIT is 1:


Internal version only: isa v30.44v30.42, AdvSIMD v27.08, pseudocode v8.5-2019-06_rc2-5-g22901f2future-20190403, sve v2019-06_rc4v8.5-00bet10_rc5 ; Build timestamp: 2019-06-26T222019-04-17T09:0458

Copyright © 2010-2019 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.

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