SQDECP (vector)

Signed saturating decrement vector by count of true predicate elements

Counts the number of true elements in the source predicate and then uses the result to decrement all destination vector elements. The results are saturated to the element signed integer range.

The predicate size specifier may be omitted in assembler source code, but this is deprecated and will be prohibited in a future release of the architecture.

Encoding: SVE

Variants: FEAT_SVE || FEAT_SME (FEAT_SVE || FEAT_SME)

313029282726252423222120191817161514131211109876543210
001001011010101000000
sizeDUopcPmZdn

SQDECP <Zdn>.<T>, <Pm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
if size == '00' then EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer m = UInt(Pm);
constant integer dn = UInt(Zdn);
constant boolean unsigned = FALSE;

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(VL) operand1 = Z[dn, VL];
constant bits(PL) operand2 = P[m, PL];
bits(VL) result;
integer count = 0;

for e = 0 to elements-1
    if ActivePredicateElement(operand2, e, esize) then
        count = count + 1;

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

Z[dn, VL] = result;

Explanations

<Zdn>: Is the name of the source and destination scalable vector register, encoded in the "Zdn" field.
<T>: <Pm>: Is the name of the source scalable predicate register, encoded in the "Pm" field.

Operational Notes

This instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is CONSTRAINED UNPREDICTABLE: