CNTB, CNTD, CNTH, CNTW

Set scalar to multiple of predicate constraint element count

This instruction 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
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8; let d : integer = UInt(Rd); let pat : bits(5) = pattern; let imm : integer = UInt(imm4) + 1;

Doubleword
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 64; let d : integer = UInt(Rd); let pat : bits(5) = pattern; let imm : integer = UInt(imm4) + 1;

Halfword
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 16; let d : integer = UInt(Rd); let pat : bits(5) = pattern; let imm : integer = UInt(imm4) + 1;

Word
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 32; let d : integer = UInt(Rd); let pat : bits(5) = pattern; let imm : integer = UInt(imm4) + 1;