WHILELT (predicate)

While incrementing signed scalar less than scalar

Generate a predicate that starting from the lowest numbered element is true while the incrementing value of the first, signed scalar operand is less than the second scalar operand and false thereafter up to the highest numbered element.

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 first general-purpose source register is not itself updated.

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

Encoding: SVE

Variants: FEAT_SVE || FEAT_SME (FEAT_SVE || 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			1						0	0	0		0	1						0
								size			Rm								sf	U	lt	Rn					eq	Pd

WHILELT <Pd>.<T>, <R><n>, <R><m>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer rsize = 32 << UInt(sf);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer d = UInt(Pd);
constant boolean unsigned = FALSE;
constant CmpOp op = Cmp_LT;

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = Ones(PL);
bits(rsize) operand1 = X[n, rsize];
constant bits(rsize) operand2 = X[m, rsize];
bits(PL) result;
boolean last = TRUE;
constant integer psize = esize DIV 8;

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;
    constant bit pbit = if last then '1' else '0';
    Elem[result, e, psize] = ZeroExtend(pbit, psize);
    operand1 = operand1 + 1;

PSTATE. = PredTest(mask, result, esize);
P[d, PL] = result;

Explanations

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