WHILEHI (predicate) -- A64

This instruction generates a predicate that starting from the highest numbered element is true while the decrementing value of the first, unsigned scalar operand is higher than the second scalar operand and false thereafter down to the lowest numbered element.

The full width of the scalar operands is significant for the purposes of comparison, and the full width first operand is decremented by one for each destination predicate element, irrespective of the predicate result element size. The first general-purpose source register is not itself updated.

The predicate result is placed in the predicate destination register. This instruction sets the First (N), None (Z), and !Last (C) condition flags based on the predicate result, and sets the V flag to zero.

SVE2
(FEAT_SVE2 || FEAT_SME)

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	Rm					0	0	0	sf	1	0	Rn					1	Pd
																				U	lt						eq

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let rsize : integer{} = 32 << UInt(sf); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let d : integer = UInt(Pd); let unsigned : boolean = TRUE; let op : CmpOp = Cmp_GT;

Assembler Symbols

<Pd>	Is the name of the destination scalable predicate register, encoded in the "Pd" field.

<T>

Is the size specifier, encoded in size:

size	<T>
00	B
01	H
10	S
11	D

<R>

Is a width specifier, encoded in sf:

sf	<R>
0	W
1	X

<n>	Is the number [0-30] of the source general-purpose register or the name ZR (31), encoded in the "Rn" field.

<m>	Is the number [0-30] of the source general-purpose register or the name ZR (31), encoded in the "Rm" field.

Operation

CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let mask : bits(PL) = Ones{}; var operand1 : bits(rsize) = X{}(n); let operand2 : bits(rsize) = X{}(m); var result : bits(PL); var last : boolean = TRUE; let psize : integer{} = esize DIV 8; let element2 : integer = if unsigned then UInt(operand2) else SInt(operand2); for e = elements-1 downto 0 do let element1 : integer = if unsigned then UInt(operand1) else SInt(operand1); var cond : boolean; case op of when Cmp_GT => cond = (element1 > element2); when Cmp_GE => cond = (element1 >= element2); end; last = last && cond; let pbit : bit = if last then '1' else '0'; result[e*:psize] = ZeroExtend{psize}(pbit); operand1 = operand1 - 1; end; PSTATE.[N,Z,C,V] = PredTest{PL}(mask, result, esize); P{PL}(d) = result;

2025-12_rel 2025-12-10 16:41:45