auto.h

/*
 * Copyright (c) The mlkem-native project authors
 * SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
 */

/* References
 * ==========
 *
 * - [HYBRID]
 *   Hybrid scalar/vector implementations of Keccak and SPHINCS+ on AArch64
 *   Becker, Kannwischer
 *   https://eprint.iacr.org/2022/1243
 */

#ifndef MLK_FIPS202_NATIVE_AARCH64_AUTO_H
#define MLK_FIPS202_NATIVE_AARCH64_AUTO_H
/* Default FIPS202 assembly profile for AArch64 systems */

/*
 * Default logic to decide which implementation to use.
 *
 */

/*
 * Keccak-f1600
 *
 * - On Arm-based Apple CPUs, or if MLK_SYS_AARCH64_FAST_SHA3 is set,
 *   we pick a pure Neon implementation.
 * - Otherwise, unless MLK_SYS_AARCH64_SLOW_BARREL_SHIFTER is set,
 *   we use lazy-rotation scalar assembly from @[HYBRID].
 * - Otherwise, if MLK_SYS_AARCH64_SLOW_BARREL_SHIFTER is set, we
 *   fall back to the standard C implementation.
 */
#if defined(__ARM_FEATURE_SHA3) && \
    (defined(__APPLE__) || defined(MLK_SYS_AARCH64_FAST_SHA3))
#include "x1_v84a.h"
#elif !defined(MLK_SYS_AARCH64_SLOW_BARREL_SHIFTER)
#include "x1_scalar.h"
#endif

/* Batched, SIMD-based Keccak-f1600 implementations. */
#if defined(MLK_SYS_AARCH64_NEON)

/*
 * Keccak-f1600x2/x4
 *
 * The optimal implementation is highly CPU-specific; see @[HYBRID].
 *
 * For now, if v8.4-A is not implemented, we fall back to Keccak-f1600.
 * If v8.4-A is implemented and we are on an Apple CPU or
 * MLK_SYS_AARCH64_FAST_SHA3 is set, we use a plain Neon-based
 * implementation.
 * Otherwise, if v8.4-A is implemented, we use a scalar/Neon/Neon hybrid.
 * The reason for this distinction is that Apple CPUs (and CPUs flagged with
 * MLK_SYS_AARCH64_FAST_SHA3) implement the SHA3 instructions on all SIMD
 * units, while Arm CPUs prior to Cortex-X4 don't, and ordinary Neon
 * instructions are still needed.
 */
#if defined(__ARM_FEATURE_SHA3)
/*
 * For Apple-M cores (and CPUs flagged with MLK_SYS_AARCH64_FAST_SHA3), we
 * use a plain implementation leveraging SHA3 instructions only.
 */
#if defined(__APPLE__) || defined(MLK_SYS_AARCH64_FAST_SHA3)
#include "x2_v84a.h"
#else
#include "x4_v8a_v84a_scalar.h"
#endif

#else /* __ARM_FEATURE_SHA3 */

#include "x4_v8a_scalar.h"

#endif /* !__ARM_FEATURE_SHA3 */

#endif /* MLK_SYS_AARCH64_NEON */

#endif /* !MLK_FIPS202_NATIVE_AARCH64_AUTO_H */