wrffr
Write First-Fault Register.
Pseudocode Operation
No pseudocode available.
Encoding
Related
More in SVE
Reference
Instruction Forms
| Encoding | Instruction | ISA | Bit pattern | ||
|---|---|---|---|---|---|
| 0x25289000 | WRFFR <Pn>.B | A64 | 00 | 100101 | 0 | 0 | 10 | 1000100100 | 0 | Pn | 0 | 0 | 0 | 00 |
Description
Read the source predicate register and place in the first-fault register (FFR). This instruction is intended to restore a saved FFR and is not recommended for general use by applications. This instruction requires that the source predicate contains a monotonic predicate value, in which starting from bit 0 there are zero or more 1 bits, followed only by 0 bits in any remaining bit positions. If the source is not a monotonic predicate value, then the resulting value in the FFR will be UNPREDICTABLE. It is not possible to generate a non-monotonic value in FFR when using SETFFR followed by first-fault or non-fault loads. This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.
Operation
CheckNonStreamingSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
bits(PL) operand = P[n, PL];
constant integer hsb = HighestSetBit(operand);
if hsb < 0 || IsOnes(operand<hsb:0>) then
FFR[PL] = operand;
else // not a monotonic predicate
FFR[PL] = bits(PL) UNKNOWN;