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CNTB, CNTD, CNTH, CNTW

Set scalar to 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 places the result in 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

 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 1 0 0 0 0 1 0 imm4 1 1 1 0 0 0 pattern Rd size<1> size<0>

CNTB <Xd>{, <pattern>{, MUL #<imm>}}

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

Doubleword

 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 1 0 0 1 1 1 0 imm4 1 1 1 0 0 0 pattern Rd size<1> size<0>

CNTD <Xd>{, <pattern>{, MUL #<imm>}}

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

Halfword

 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 1 0 0 0 1 1 0 imm4 1 1 1 0 0 0 pattern Rd size<1> size<0>

CNTH <Xd>{, <pattern>{, MUL #<imm>}}

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

Word

 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 1 0 0 1 0 1 0 imm4 1 1 1 0 0 0 pattern Rd size<1> size<0>

CNTW <Xd>{, <pattern>{, MUL #<imm>}}

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

Assembler Symbols

 Is the 64-bit name of the destination general-purpose register, encoded in the "Rd" 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
 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);

X[d] = (count * imm)<63:0>;```

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 registers.
• 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 registers.
• The values of the NZCV flags.