Unsigned saturating decrement scalar by count of true predicate elements
This instruction determines the number of true elements in the source predicate and then uses the result to decrement the scalar destination. The result is saturated to the general-purpose register's unsigned integer range.
It has encodings from 2 classes: 32-bit and 64-bit
| 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 | 1 | 0 | 0 | 1 | 0 | 1 | size | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | Pm | Rdn | ||||||||
| D | U | sf | op | ||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let m : integer = UInt(Pm); let dn : integer = UInt(Rdn); let unsigned : boolean = TRUE; let ssize : integer{} = 32;
| 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 | 1 | 0 | 0 | 1 | 0 | 1 | size | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | Pm | Rdn | ||||||||
| D | U | sf | op | ||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let m : integer = UInt(Pm); let dn : integer = UInt(Rdn); let unsigned : boolean = TRUE; let ssize : integer{} = 64;
| <Wdn> |
Is the 32-bit name of the source and destination general-purpose register, encoded in the "Rdn" field. |
| <Pm> |
Is the name of the source scalable predicate register, encoded in the "Pm" field. |
| <T> |
Is the size specifier,
encoded in
|
| <Xdn> |
Is the 64-bit name of the source and destination general-purpose register, encoded in the "Rdn" field. |
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let operand1 : bits(ssize) = X{}(dn); let operand2 : bits(PL) = P{}(m); var result : bits(ssize); var count : integer = 0; for e = 0 to elements-1 do if ActivePredicateElement{PL}(operand2, e, esize) then count = count + 1; end; end; if unsigned then (result, -) = UnsignedSatQ{ssize}(UInt(operand1) - count); X{64}(dn) = ZeroExtend{64}(result); else (result, -) = SignedSatQ{ssize}(SInt(operand1) - count); X{64}(dn) = SignExtend{64}(result); end;
If FEAT_SME is implemented and the PE is in Streaming SVE mode, then any subsequent instruction that is dependent on the general-purpose register written by this instruction might be significantly delayed.
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