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BRKB, BRKBS

Break before first true condition.

Sets destination predicate elements up to but not including the first active and true source element to true, then sets subsequent elements to false. Inactive elements in the destination predicate register remain unmodified or are set to zero, depending on whether merging or zeroing predication is selected. Optionally sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and the V flag to zero.

It has encodings from 2 classes: Not setting the condition flags and Setting the condition flags

Not setting the condition flags

313029282726252423222120191817161514131211109876543210
001001011001000001Pg0PnMPd

Not setting the condition flags

BRKB <Pd>.B, <Pg>/<ZM>, <Pn>.B

if !HaveSVE() then UNDEFINED;
integer esize = 8;
integer g = UInt(Pg);
integer n = UInt(Pn);
integer d = UInt(Pd);
boolean merging = (M == '1');
boolean setflags = FALSE;

Setting the condition flags

313029282726252423222120191817161514131211109876543210
001001011101000001Pg0Pn0Pd

Setting the condition flags

BRKBS <Pd>.B, <Pg>/Z, <Pn>.B

if !HaveSVE() then UNDEFINED;
integer esize = 8;
integer g = UInt(Pg);
integer n = UInt(Pn);
integer d = UInt(Pd);
boolean merging = FALSE;
boolean setflags = TRUE;

Assembler Symbols

<Pd>

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

<Pg>

Is the name of the governing scalable predicate register, encoded in the "Pg" field.

<ZM> Is the predication qualifier, encoded in M:
M <ZM>
0 Z
1 M
<Pn>

Is the name of the source scalable predicate register, encoded in the "Pn" field.

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(PL) operand  = P[n];
bits(PL) operand2 = P[d];
boolean break = FALSE;
bits(PL) result;

for e = 0 to elements-1
    boolean element = ElemP[operand, e, esize] == '1';
    if ElemP[mask, e, esize] == '1' then
        break = break || element;
        ElemP[result, e, esize] = if !break then '1' else '0';
    elsif merging then
        ElemP[result, e, esize] = ElemP[operand2, e, esize];
    else
        ElemP[result, e, esize] = '0';

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