UQDECB

Unsigned saturating decrement scalar by multiple of 8-bit predicate constraint element count

Determines the number of active 8-bit elements implied by the named predicate constraint, multiplies that by an immediate in the range 1 to 16 inclusive, and then uses the result to decrement the scalar destination. The result is saturated to the general-purpose register's unsigned integer range.

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 2 classes: 32-bit and 64-bit

32-bit

if !HaveSVE() && !HaveSME() then UNDEFINED; integer esize = 8; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1; boolean unsigned = TRUE; integer ssize = 32;

64-bit

if !HaveSVE() && !HaveSME() then UNDEFINED; integer esize = 8; integer dn = UInt(Rdn); bits(5) pat = pattern; integer imm = UInt(imm4) + 1; boolean unsigned = TRUE; integer ssize = 64;