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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Fast but weak random generator.
#if defined(LIB_JXL_XORSHIFT128PLUS_INL_H_) == defined(HWY_TARGET_TOGGLE)
#ifdef LIB_JXL_XORSHIFT128PLUS_INL_H_
#undef LIB_JXL_XORSHIFT128PLUS_INL_H_
#else
#define LIB_JXL_XORSHIFT128PLUS_INL_H_
#endif
#include <stddef.h>
#include <hwy/highway.h>
HWY_BEFORE_NAMESPACE();
namespace jxl {
namespace HWY_NAMESPACE {
namespace {
// These templates are not found via ADL.
using hwy::HWY_NAMESPACE::ShiftLeft;
using hwy::HWY_NAMESPACE::ShiftRight;
// Adapted from https://github.com/vpxyz/xorshift/blob/master/xorshift128plus/
// (MIT-license)
class Xorshift128Plus {
public:
// 8 independent generators (= single iteration for AVX-512)
enum { N = 8 };
explicit HWY_MAYBE_UNUSED Xorshift128Plus(const uint64_t seed) {
// Init state using SplitMix64 generator
s0_[0] = SplitMix64(seed + 0x9E3779B97F4A7C15ull);
s1_[0] = SplitMix64(s0_[0]);
for (size_t i = 1; i < N; ++i) {
s0_[i] = SplitMix64(s1_[i - 1]);
s1_[i] = SplitMix64(s0_[i]);
}
}
HWY_MAYBE_UNUSED Xorshift128Plus(const uint32_t seed1, const uint32_t seed2,
const uint32_t seed3, const uint32_t seed4) {
// Init state using SplitMix64 generator
s0_[0] = SplitMix64(((static_cast<uint64_t>(seed1) << 32) + seed2) +
0x9E3779B97F4A7C15ull);
s1_[0] = SplitMix64(((static_cast<uint64_t>(seed3) << 32) + seed4) +
0x9E3779B97F4A7C15ull);
for (size_t i = 1; i < N; ++i) {
s0_[i] = SplitMix64(s0_[i - 1]);
s1_[i] = SplitMix64(s1_[i - 1]);
}
}
HWY_INLINE HWY_MAYBE_UNUSED void Fill(uint64_t* HWY_RESTRICT random_bits) {
#if HWY_CAP_INTEGER64
const HWY_FULL(uint64_t) d;
for (size_t i = 0; i < N; i += Lanes(d)) {
auto s1 = Load(d, s0_ + i);
const auto s0 = Load(d, s1_ + i);
const auto bits = s1 + s0; // b, c
Store(s0, d, s0_ + i);
s1 ^= ShiftLeft<23>(s1);
Store(bits, d, random_bits + i);
s1 ^= s0 ^ ShiftRight<18>(s1) ^ ShiftRight<5>(s0);
Store(s1, d, s1_ + i);
}
#else
for (size_t i = 0; i < N; ++i) {
auto s1 = s0_[i];
const auto s0 = s1_[i];
const auto bits = s1 + s0; // b, c
s0_[i] = s0;
s1 ^= s1 << 23;
random_bits[i] = bits;
s1 ^= s0 ^ (s1 >> 18) ^ (s0 >> 5);
s1_[i] = s1;
}
#endif
}
private:
static uint64_t SplitMix64(uint64_t z) {
z = (z ^ (z >> 30)) * 0xBF58476D1CE4E5B9ull;
z = (z ^ (z >> 27)) * 0x94D049BB133111EBull;
return z ^ (z >> 31);
}
HWY_ALIGN uint64_t s0_[N];
HWY_ALIGN uint64_t s1_[N];
};
} // namespace
// NOLINTNEXTLINE(google-readability-namespace-comments)
} // namespace HWY_NAMESPACE
} // namespace jxl
HWY_AFTER_NAMESPACE();
#endif // LIB_JXL_XORSHIFT128PLUS_INL_H_
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