whilelo

SVE While Lower (Unsigned)

WHILELO <Pd>.<T>, <Xn>, <Xm>

Generates predicate for unsigned loop (while Xn < Xm).

Pseudocode Operation

element_size ← size_in_bytes(<T>)
for i = 0 to VL/element_size-1
  if (Xn + i) < Xm then
    Pd[i] ← 1
  else
    Pd[i] ← 0
  endif
endfor

Example

WHILELO p0.T, x1, x2

Encoding

Binary Layout

00100101

31:24

size

23:22

1

21

Rm

20:16

000

15:13

sf

12

1

11

1

10

Rn

9:5

0

4

Pd

3:0

 

Format SVE Compare

Opcode 0x25200C00

Extension SVE

Operands

• Pd
  Destination predicate register (SVE)
• Xn
  Start
• Xm
  Limit

Related

More in SVE

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x25200C00	WHILELO <Pd>.<T>, <R><n>, <R><m>		A64		00100101 | size | 1 | Rm | 000 | sf | 1 | 1 | Rn | 0 | Pd
0x25204C10	WHILELO <PNd>.<T>, <Xn>, <Xm>, <vl>		A64		00100101 | size | 1 | Rm | 01 | vl | 0 | 1 | 1 | Rn | 1 | 0 | PNd
0x25205C10	WHILELO { <Pd1>.<T>, <Pd2>.<T> }, <Xn>, <Xm>		A64		00100101 | size | 1 | Rm | 0101 | 1 | 1 | Rn | 1 | Pd | 0

Description

Generate a predicate that starting from the lowest numbered element is true while the incrementing value of the first, unsigned scalar operand is lower 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.

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
bits(PL) mask = Ones(PL);
bits(rsize) operand1 = X[n, rsize];
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;
    bit pbit = if last then '1' else '0';
    Elem[result, e, psize] = ZeroExtend(pbit, psize);
    operand1 = operand1 + 1;

PSTATE.<N,Z,C,V> = PredTest(mask, result, esize);
P[d, PL] = result;