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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
GATHER = 0x39
## Format
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x39(GATHER) | Elt_size | Is_modified | Num_elts | Surface | Global_offset | Element_offset |
| | Dst | | | | | |
## Semantics
for (i = 0; i < exec_size; ++i) {
if (ChEn[i]) {
dst[i] = surface[global_offset+element_offset[i]]; //1, 2, or 4 byte
}
}
## Description
Performs 1, 8, or 16 element scattered read from <surface> and stores the result into <dst>.
- **Elt_size(ub):**
- Bit[1..0]: encodes the byte size of each element
- 0b00: 1 byte
- 0b01: 2 bytes
- 0b10: 4 bytes
- **Is_modified(ub):** The field is ignored, the read always return the last write from this thread
- **Num_elts(ub):**
- Bit[1..0]: encodes the number of elements that will be read
- 0b00: 8 elements
- 0b01: 16 elements
- 0b10: 1 element
- Bit[7..4]: encodes the execution mask as described in Table 4.
- **Surface(ub):** Index of the surface variable. It must be a buffer. Valid values are:
- 0: T0 - Shared Local Memory (SLM) access
- 5: T255 - Stateless surface access
- **Global_offset(scalar):** The global offset of all elements, in the unit of element size. Must have type UD
- **Element_offset(raw_operand):** The first Num_elts elements will be used as the offsets (after adding the global offset) into the surface, and they are in the unit of element size. Must have type UD
- **Dst(raw_operand):** The variable storing the results of the read. The first num_elts elements will be written to. For 1 and 2 byte accesses the upper bytes have undefined values. Must have type UD,D,F
#### Properties
- **Out-of-bound Access:** On read: zeros are returned.
## Text
```
GATHER.<elt_size> <surface> <global_offset> <element_offset> <dst>
```
## Notes
|
