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UQDECD (vector)

Unsigned saturating decrement vector by multiple of 64-bit predicate constraint element count.

Determines the number of active 64-bit 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 all destination vector elements. The results are saturated to the 64-bit unsigned integer range.

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.

313029282726252423222120191817161514131211109876543210
000001001110imm4110011patternZdn

SVE

UQDECD <Zdn>.D{, <pattern>{, MUL #<imm>}}

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

Assembler Symbols

<Zdn>

Is the name of the source and destination scalable vector register, encoded in the "Zdn" field.

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

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

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
integer count = DecodePredCount(pat, esize);
bits(VL) operand1 = Z[dn];
bits(VL) result;

for e = 0 to elements-1
    integer element1 = Int(Elem[operand1, e, esize], unsigned);
    (Elem[result, e, esize], -) = SatQ(element1 - (count * imm), esize, unsigned);

Z[dn] = result;

Operational information

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.