Base Instructions | SIMD&FP Instructions | SVE Instructions | SME Instructions | Index by Encoding | Shared Pseudocode | Proprietary Notice

## LDFF1H (scalar plus scalar)

Contiguous load first-fault unsigned halfwords to vector (scalar index)

Contiguous load with first-faulting behavior of unsigned halfwords to elements of a vector register from the memory address generated by a 64-bit scalar base and scalar index which is multiplied by 2 and added to the base address. After each element access the index value is incremented, but the index register is not updated. Inactive elements will not cause a read from Device memory or signal a fault, and are set to zero in the destination vector.

This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.

It has encodings from 3 classes: 16-bit element , 32-bit element and 64-bit element

### 16-bit element

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
1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | Rm | 0 | 1 | 1 | Pg | Rn | Zt
| dtype<3:1> | dtype<0> |  |  |  |  |

####

LDFF1H { <Zt>.H }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #1}]

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer g = UInt(Pg); constant integer esize = 16; constant integer msize = 16; constant boolean unsigned = TRUE;

### 32-bit element

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
1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | Rm | 0 | 1 | 1 | Pg | Rn | Zt
| dtype<3:1> | dtype<0> |  |  |  |  |

####

LDFF1H { <Zt>.S }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #1}]

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer g = UInt(Pg); constant integer esize = 32; constant integer msize = 16; constant boolean unsigned = TRUE;

### 64-bit element

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
1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | Rm | 0 | 1 | 1 | Pg | Rn | Zt
| dtype<3:1> | dtype<0> |  |  |  |  |

####

LDFF1H { <Zt>.D }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #1}]

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer g = UInt(Pg); constant integer esize = 64; constant integer msize = 16; constant boolean unsigned = TRUE;

### Assembler Symbols

<Zt> | Is the name of the scalable vector register to be transferred, encoded in the "Zt" field.

<Pg> | Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Xn|SP> | Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

<Xm> | Is the optional 64-bit name of the general-purpose offset register, defaulting to XZR, encoded in the "Rm" field.

### Operation

CheckNonStreamingSVEEnabled(); constant integer VL = CurrentVL; constant integer PL = VL DIV 8; constant integer elements = VL DIV esize; bits(64) base; constant bits(PL) mask = P[g, PL]; bits(VL) result; constant bits(VL) orig = Z[t, VL]; bits(msize) data; bits(64) offset; bits(64) addr; constant integer mbytes = msize DIV 8; boolean fault = FALSE; boolean faulted = FALSE; boolean unknown = FALSE; constant boolean contiguous = TRUE; constant boolean tagchecked = TRUE; AccessDescriptor accdesc = CreateAccDescSVEFF(contiguous, tagchecked); if !AnyActiveElement(mask, esize) then if n == 31 && ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then CheckSPAlignment(); else if n == 31 then CheckSPAlignment(); base = if n == 31 then SP[] else X[n, 64]; offset = X[m, 64]; addr = AddressAdd(base, UInt(offset) * mbytes, accdesc); assert accdesc.first; for e = 0 to elements-1 if ActivePredicateElement(mask, e, esize) then if accdesc.first then // Mem[] will not return if a fault is detected for the first active element data = Mem[addr, mbytes, accdesc]; accdesc.first = FALSE; else // MemNF[] will return fault=TRUE if access is not performed for any reason (data, fault) = MemNF[addr, mbytes, accdesc]; else (data, fault) = (Zeros(msize), FALSE); addr = AddressIncrement(addr, mbytes, accdesc); // FFR elements set to FALSE following a suppressed access/fault faulted = faulted || fault; if faulted then ElemFFR[e, esize] = '0'; // Value becomes CONSTRAINED UNPREDICTABLE after an FFR element is FALSE unknown = unknown || ElemFFR[e, esize] == '0'; if unknown then if !fault && ConstrainUnpredictableBool(Unpredictable_SVELDNFDATA) then Elem[result, e, esize] = Extend(data, esize, unsigned); elsif ConstrainUnpredictableBool(Unpredictable_SVELDNFZERO) then Elem[result, e, esize] = Zeros(esize); else // merge Elem[result, e, esize] = Elem[orig, e, esize]; else Elem[result, e, esize] = Extend(data, esize, unsigned); Z[t, VL] = result;

Base Instructions | SIMD&FP Instructions | SVE Instructions | SME Instructions | Index by Encoding | Shared Pseudocode | Proprietary Notice

Internal version only: aarchmrs v2024-03_relA, pseudocode v2024-03_rel, sve v2024-03_rel ; Build timestamp: 2024-03-26T09:45

Copyright © 2010-2024 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.