You copied the Doc URL to your clipboard.

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

313029282726252423222120191817161514131211109876543210
000001000010imm4111000patternRd
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

313029282726252423222120191817161514131211109876543210
000001001110imm4111000patternRd
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

313029282726252423222120191817161514131211109876543210
000001000110imm4111000patternRd
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

313029282726252423222120191817161514131211109876543210
000001001010imm4111000patternRd
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

<Xd>

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
<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);

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.