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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
GATHER_SCALED = 0x78
## Format
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x78(GATHER_SCALED) | Exec_size | Pred | Block_size | Num_blocks | Scale | Surface |
| | Offset | Element_offset | Dst | | | |
## Semantics
for (i = 0; i < exec_size; ++i) {
if (ChEn[i]) {
dst[i] = surface[offset+element_offset[i]]; //<num_blocks> bytes
}
}
## Description
Performs <exec_size> element scattered read from <surface> and stores the results into <dst>. For each channel <num_blocks> bytes are read. The address to be read is determined by the offset and each element offset.
- **Exec_size(ub):** Execution size
- Bit[2..0]: size of the region for source and destination operands
- 0b000: 1 element (scalar)
- 0b001: 2 elements
- 0b010: 4 elements
- 0b011: 8 elements
- 0b100: 16 elements
- 0b101: 32 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
- **Block_size(ub):** This field is ignored and block size is always one byte
- **Num_blocks(ub):**
- Bit[1..0]: encodes the number of blocks to read at each address.
- 0b00: 1 block
- 0b01: 2 blocks
- 0b10: 4 blocks
- **Scale(uw):** This field is ignored and scale is always zero
- **Surface(ub):** Index of the surface variable. When scale is non-zero, only T0 (SLM) and T5 (stateless) are supported
- **Offset(scalar):** The global byte offset. Must have type UD
- **Element_offset(raw_operand):** The first Exec_size elements of the operand will be used as the byte offsets into the surface. Must have type UD
- **Dst(raw_operand):** The variable storing the results of the read. For 1 and 2 byte reads the upper bytes have undefined values. Must have type UD,D,F
#### Properties
- **Out-of-bound Access:** On read: zeros are returned.
## Text
```
[(<P>)] GATHER_SCALED.<num_blocks> (<exec_size>) <surface> <offset> <element_offset> <dst>
```
## Notes
|
