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GEMINI.md: Update Arm wording and guidance

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Update trademarks, document `arm_sve.h` and add guidance to prefer fully
predicated loop iterations for SVE/SME implementations.

Change-Id: I4039b982ba816193019df62a523fd29f474c3d10
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/8256407
Reviewed-by: Wan-Teh Chang <wtc@google.com>
Reviewed-by: Frank Barchard <fbarchard@google.com>
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George Steed 2026-08-18 11:57:10 +01:00 committed by Frank Barchard
parent f61a589bb3
commit 26e56be0f9
1 changed files with 26 additions and 10 deletions
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@ -22,15 +22,20 @@ and compiler compatibility.
`-DLIBYUV_ENABLE_ROWWIN`.
* **Note**: Use either `row_gcc` or `row_win`, never both.
### ARM Architectures
### Arm Architecture (32-bit)
* **row_neon.cc**: 32-bit ARM. Written entirely in inline assembly for
* **row_neon.cc**: 32-bit Arm. Written entirely in inline assembly for
GCC/Clang.
* **row_neon64.cc**: 64-bit ARM (AArch64). Written entirely in inline assembly
for GCC/Clang.
* **row_sve.cc**: ARMv9 Scalable Vector Extensions (SVE).
* **row_sme.cc**: ARMv9 Scalable Matrix Extension (SME) and Streaming SVE
### Arm Architecture (AArch64) (64-bit)
* **row_neon64.cc**: 64-bit Arm (AArch64) Neon. Written entirely in inline
assembly for GCC/Clang.
* **row_sve.cc**: Armv9 Scalable Vector Extension (SVE2).
* **row_sme.cc**: Armv9 Scalable Matrix Extension (SME) and Streaming SVE
(SSVE).
* **row_sve.h**: Streaming-compatible implementations shared across
**row_sve.cc** and **row_sme.cc**.
### Other Architectures
@ -43,16 +48,27 @@ and compiler compatibility.
* **row_common.cc**: Portable C/C++ versions. This is the reference
implementation.
* **row_any.cc**: Handles "remainder" pixels for widths not multiples of SIMD
register size. Used for x86, NEON, and MIPS. Not required for SVE, SME, or
register size. Used for x86, Neon, and MIPS. Not required for SVE2, SME, or
RVV due to hardware-level masking.
## Coding Guidelines
1. **Feature Macros**: Use the `HAS_` macros in `include/libyuv/row.h` to
enable or disable specific instruction set extensions.
### x86 Architectures (32-bit and 64-bit)
1. **AVX512 Logic**: AVX512 row functions are strictly enabled for **64-bit x86
only**.
2. **Feature Macros**: Use the `HAS_` macros in `include/libyuv/row.h` to
enable or disable specific AVX512 versions.
3. **MSVC Intrinsics (`row_win.cc`)**: When converting `row_gcc.cc` to `row_win.cc`, use `_mm512_permutex2var_epi8`, not `_mm512_permi2var_epi8` intrinsic.
2. **MSVC Intrinsics (`row_win.cc`)**: When converting `row_gcc.cc` to
`row_win.cc`, use `_mm512_permutex2var_epi8`, not `_mm512_permi2var_epi8`
intrinsic.
### AArch64
1. For SVE2/SME, aim to use full predicates (`ptrue`) and full vectors for the
main loop body and use predication only to mask the tail loop as needed.
Pointer updates should be done with `inc[bhwd]` or `add`, not by `incp`.
## Changelist (CL) Format Guidelines