WHILELS (predicate as counter)

While incrementing unsigned scalar lower or same as scalar (predicate-as-counter)

Generate a predicate for a group of two or four vectors that starting from the lowest numbered element of the group is true while the incrementing value of the first, unsigned scalar operand is lower or same as the second scalar operand and false thereafter up to the highest numbered element of the group.

If the second scalar operand is equal to the maximum unsigned integer value then a condition which includes an equality test can never fail and the result will be an all-true predicate.

The full width of the scalar operands is significant for the purposes of comparison, and the full width first operand is incremented by one for each destination predicate element, irrespective of the predicate result element size.

The predicate result is placed in the predicate destination register using the predicate-as-counter encoding. Sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and the V flag to zero.

Encoding: SVE2

Variants: FEAT_SME2 || FEAT_SVE2p1 (FEAT_SME2 || FEAT_SVE2p1)

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			1						0	1		0	1	1						1	1
								size			Rm							vl		U	lt	Rn						eq	PNd

WHILELS <PNd>.<T>, <Xn>, <Xm>, <vl>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SME2) && !IsFeatureImplemented(FEAT_SVE2p1) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer rsize = 64;
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer d = UInt('1':PNd);
constant boolean unsigned = TRUE;
constant boolean invert = FALSE;
constant CmpOp op = Cmp_LE;
constant integer width = 2 << UInt(vl);

Operation

if IsFeatureImplemented(FEAT_SVE2p1) then CheckSVEEnabled(); else CheckStreamingSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = width * (VL DIV esize);
bits(rsize) operand1 = X[n, rsize];
constant bits(rsize) operand2 = X[m, rsize];
bits(PL) result;
boolean last = TRUE;
integer count = 0;

for e = 0 to elements-1
    boolean cond;
    case op of
        when Cmp_LT cond = (Int(operand1, unsigned) <  Int(operand2, unsigned));
        when Cmp_LE cond = (Int(operand1, unsigned) <= Int(operand2, unsigned));

    last = last && cond;
    if last then count = count + 1;
    operand1 = operand1 + 1;

result = EncodePredCount(esize, elements, count, invert, PL);
PSTATE. = PredCountTest(elements, count, invert);
P[d, PL] = result;

Explanations

<PNd>: Is the name of the destination scalable predicate register PN8-PN15, with predicate-as-counter encoding, encoded in the "PNd" field.
<T>: <Xn>: Is the 64-bit name of the first source general-purpose register, encoded in the "Rn" field.
<Xm>: Is the 64-bit name of the second source general-purpose register, encoded in the "Rm" field.
<vl>: