string-hasher.cc

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// Copyright 2024 the V8 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.
 
#include "src/strings/string-hasher.h"
 
#include "src/strings/string-hasher-inl.h"
 
namespace v8::internal {
 
struct ConvertTo8BitHashReader {
  static constexpr unsigned kCompressionFactor = 2;
  static constexpr unsigned kExpansionFactor = 1;
 
  V8_INLINE static uint64_t Read64(const uint8_t* ptr) {
    const uint16_t* p = reinterpret_cast<const uint16_t*>(ptr);
    DCHECK_LE(p[0], 0xff);
    DCHECK_LE(p[1], 0xff);
    DCHECK_LE(p[2], 0xff);
    DCHECK_LE(p[3], 0xff);
    DCHECK_LE(p[4], 0xff);
    DCHECK_LE(p[5], 0xff);
    DCHECK_LE(p[6], 0xff);
    DCHECK_LE(p[7], 0xff);
#ifdef __SSE2__
    __m128i x = _mm_loadu_si128(reinterpret_cast<const __m128i*>(p));
    return _mm_cvtsi128_si64(_mm_packus_epi16(x, x));
#elif defined(__ARM_NEON__)
    int16x8_t x;
    memcpy(&x, p, sizeof(x));
    return vget_lane_u64(vreinterpret_u64_u8(vmovn_u16(x)), 0);
#else
    return (uint64_t{p[0]}) | (uint64_t{p[1]} << 8) | (uint64_t{p[2]} << 16) |
           (uint64_t{p[3]} << 24) | (uint64_t{p[4]} << 32) |
           (uint64_t{p[5]} << 40) | (uint64_t{p[6]} << 48) |
           (uint64_t{p[7]} << 56);
#endif
  }
 
  V8_INLINE static uint64_t Read32(const uint8_t* ptr) {
    const uint16_t* p = reinterpret_cast<const uint16_t*>(ptr);
    DCHECK_LE(p[0], 0xff);
    DCHECK_LE(p[1], 0xff);
    DCHECK_LE(p[2], 0xff);
    DCHECK_LE(p[3], 0xff);
#ifdef __SSE2__
    __m128i x = _mm_loadu_si64(reinterpret_cast<const __m128i*>(p));
    return _mm_cvtsi128_si64(_mm_packus_epi16(x, x));
#elif defined(__ARM_NEON__)
    int8x8_t x;
    memcpy(&x, p, sizeof(x));
    int16x8_t x_wide = vcombine_u64(x, x);
    return vget_lane_u32(vreinterpret_u32_u8(vmovn_u16(x_wide)), 0);
#else
    return (uint64_t{p[0]}) | (uint64_t{p[1]} << 8) | (uint64_t{p[2]} << 16) |
           (uint64_t{p[3]} << 24);
#endif
  }
 
  V8_INLINE static uint64_t ReadSmall(const uint8_t* ptr, size_t k) {
    const uint16_t* p = reinterpret_cast<const uint16_t*>(ptr);
    DCHECK_LE(p[0], 0xff);
    DCHECK_LE(p[k >> 1], 0xff);
    DCHECK_LE(p[k - 1], 0xff);
    return (uint64_t{p[0]} << 56) | (uint64_t{p[k >> 1]} << 32) | p[k - 1];
  }
};
 
namespace detail {
uint64_t HashConvertingTo8Bit(const uint16_t* chars, uint32_t length,
                              uint64_t seed) {
  return rapidhash<ConvertTo8BitHashReader>(
      reinterpret_cast<const uint8_t*>(chars), length, seed);
}
}  // namespace detail
 
}  // namespace v8::internal