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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2022 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
SVM = 0x4e
GATHER4_SCALED = 0x06
## Format
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x4e(SVM) | 0x06(GATHER4_SCALED) | Exec_size | Pred | Channels | Scale | Address | Element_offset |
| | | Dst | | | | | |
## Semantics
```
UD ch_pos = 0;
for (c = 0; c < 4; ++c) {
if (ch_mask[c] == 1) {
for (i = 0; i < exec_size; ++i) {
if (ChEn[i]) {
UD ch_start = ch_pos * max(exec_size, GRF_SIZE / 4); // GRF_SIZE is the register size in byte
dst[ch_start+i] = *(address + element_offset[i] + (c * 4)); //4 byte
}
}
ch_pos++;
}
}
```
## Description
```
Performs <exec_size>*<num_enabled_channels> element scattered read
from virtual addresses and stores the results into <dst>. The address to
be read is determined by the offset, scaling pitch, and each element
offset, and the final address must be dword-aligned.
```
- **Exec_size(ub):** Execution size
- Bit[2..0]: size of the region for source and destination operands
- 0b011: 8 elements
- 0b100: 16 elements
- Bit[7..4]: execution mask (explicit control over the enabled channels)
- 0b0000: M1
- 0b0001: M2
- 0b0010: M3
- 0b0011: M4
- 0b0100: M5
- 0b0101: M6
- 0b0110: M7
- 0b0111: M8
- 0b1000: M1_NM
- 0b1001: M2_NM
- 0b1010: M3_NM
- 0b1011: M4_NM
- 0b1100: M5_NM
- 0b1101: M6_NM
- 0b1110: M7_NM
- 0b1111: M8_NM
- **Pred(uw):** Predication control
- **Channels(ub):**
- Bit[3..0]: determines the write masks for the RGBA channel, with R being bit 0 and A bit 3. At least one channel must be enabled (i.e., "0000" is not allowed)
- **Scale(uw):** This field is ingored and scale is always zero
- **Address(scalar):** The global byte offset. Must have type UQ
- **Element_offset(raw_operand):** The first Exec_size elements of the operand will be used as the byte offsets for the corresponding channel. Must have type UQ
- **Dst(raw_operand):** The variable storing the results of the read. For each enabled channel in RGBA order, exec_size elements will be returned to dst subject to predication. The next enabled channel will have its return data starting at the next register. If a channel's return data do not occupy the entire register, the remaining part of the register has undefined values. Must have type UD,D,F
#### Properties
## Text
```
[(<P>)] SVM_GATHER4_SCALED.<channels> (<exec_size>) <address> <element_offset> <dst>
```
## Notes
|
