fnv1a.h

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#pragma once
 
#include <stddef.h>
#include <stdint.h>
 
// NOTE: This is a low-level hash utility. To avoid circular dependencies with
// asciichat_errno.h and common.h, we don't log errors here. Invalid inputs return 0.
 
/* ============================================================================
 * FNV-1a Constants
 * ============================================================================ */
 
#define FNV1A_32_OFFSET_BASIS 2166136261ULL
 
#define FNV1A_32_PRIME 16777619ULL
 
#define FNV1A_32_MASK 0xFFFFFFFFULL
 
/* ============================================================================
 * Macros
 * ============================================================================ */
 
#define FNV1A_INIT(hash) uint64_t hash = FNV1A_32_OFFSET_BASIS;
 
#define FNV1A_32_HASH(hash, byte)                                                                                      \
  do {                                                                                                                 \
    (hash) = (((hash) ^ (uint64_t)(byte)) * FNV1A_32_PRIME) & FNV1A_32_MASK;                                           \
  } while (0)
 
/* ============================================================================
 * FNV-1a Hash Functions
 * ============================================================================ */
 
static inline uint32_t fnv1a_hash_bytes(const void *data, size_t len) {
  // Return 0 for invalid input (no error logging to avoid circular dependencies)
  if (!data || len == 0) {
    return 0;
  }
 
  uint64_t hash = FNV1A_32_OFFSET_BASIS;
  const unsigned char *bytes = (const unsigned char *)data;
  const unsigned char *end = bytes + len;
 
  while (bytes < end) {
    uint64_t byte = (uint64_t)*bytes++;
    hash = ((hash ^ byte) * FNV1A_32_PRIME) & FNV1A_32_MASK;
  }
 
  return (uint32_t)hash;
}
 
static inline uint32_t fnv1a_hash_string(const char *str) {
  // Return 0 for invalid input (no error logging to avoid circular dependencies)
  if (!str) {
    return 0;
  }
 
  uint64_t hash = FNV1A_32_OFFSET_BASIS;
  const unsigned char *p = (const unsigned char *)str;
 
  while (*p) {
    uint64_t byte = (uint64_t)*p++;
    hash = ((hash ^ byte) * FNV1A_32_PRIME) & FNV1A_32_MASK;
  }
 
  return (uint32_t)hash;
}
 
static inline uint32_t fnv1a_hash_uint32(uint32_t value) {
  uint64_t hash = FNV1A_32_OFFSET_BASIS;
 
  // Hash each byte of the 32-bit value
  FNV1A_32_HASH(hash, (value >> 0) & FNV1A_32_MASK);
  FNV1A_32_HASH(hash, (value >> 8) & FNV1A_32_MASK);
  FNV1A_32_HASH(hash, (value >> 16) & FNV1A_32_MASK);
  FNV1A_32_HASH(hash, (value >> 24) & FNV1A_32_MASK);
 
  return (uint32_t)hash;
}
 
static inline uint32_t fnv1a_hash_uint64(uint64_t value) {
  uint64_t hash = FNV1A_32_OFFSET_BASIS;
 
  // Hash each byte of the 64-bit value
  for (int i = 0; i < 8; i++) {
    uint64_t byte = (value >> (i * 8)) & FNV1A_32_MASK;
    hash = ((hash ^ byte) * FNV1A_32_PRIME) & FNV1A_32_MASK;
  }
 
  return (uint32_t)hash;
}