zircon/system/ulib/zircon-internal/include/lib/zircon-internal/fnv1hash.h

// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#pragma once

#include <stdint.h>
#include <string.h>

// FNV-1a Hash
//
// http://www.isthe.com/chongo/tech/comp/fnv/index.html

#define FNV32_PRIME (16777619)
#define FNV32_OFFSET_BASIS (2166136261)

static inline uint32_t fnv1a32(const void* ptr, size_t len) {
  uint32_t n = FNV32_OFFSET_BASIS;
  const uint8_t* data = (const uint8_t*)ptr;
  while (len-- > 0) {
    n = (n ^ (*data++)) * FNV32_PRIME;
  }
  return n;
}

#define FNV64_PRIME (1099511628211ULL)
#define FNV64_OFFSET_BASIS (14695981039346656037ULL)

static inline uint64_t fnv1a64(const void* ptr, size_t len) {
  uint64_t n = FNV64_OFFSET_BASIS;
  const uint8_t* data = (const uint8_t*)ptr;
  while (len-- > 0) {
    n = (n ^ (*data++)) * FNV64_PRIME;
  }
  return n;
}

// for bits 0..15
static inline uint32_t fnv1a_tiny(uint32_t n, uint32_t bits) {
  uint32_t hash = FNV32_OFFSET_BASIS;
  hash = (hash ^ (n & 0xFF)) * FNV32_PRIME;
  n >>= 8;
  hash = (hash ^ (n & 0xFF)) * FNV32_PRIME;
  n >>= 8;
  hash = (hash ^ (n & 0xFF)) * FNV32_PRIME;
  n >>= 8;
  hash = (hash ^ n) * FNV32_PRIME;
  return ((hash >> bits) ^ hash) & ((1 << bits) - 1);
}

#define fnv1a32str(str) fnv1a32(str, strlen(str))
#define fnv1a64str(str) fnv1a64(str, strlen(str))