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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
SCATTER4_SCALED = 0x75
## Format
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x75(SCATTER4_SCALED) | Exec_size | Pred | Channels | Scale | Surface | Offset |
| | Element_offset | Src | | | | |
## 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 bytes
surface[(address/4)+c] = src[ch_start+i]; //4 bytes
}
}
ch_pos++;
}
}
## Description
Performs <exec_size>*<num_enabled_channels> element scattered write into <surface>, using the values from <src>. The address to be written 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 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
- **Src(raw_operand):** The values to be written. For each enabled channel in RGBA order, exec_size elements will be written to the surface subject to predication. The next enabled channel will get its data from the next register. Must have type UD,D,F
#### Properties
- **Out-of-bound Access:** On write: data is dropped.
## Text
```
[(<P>)] SCATTER4_SCALED.<channels> (<exec_size>) <surface> <offset> <element_offset> <src>
```
## Notes
The behavior is undefined if more than one channel writes to the same address.
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