Hashing and Checksums¶

Header: libxs_hash.h

Hash functions for buffers, fixed-width keys, and strings. The default hash uses hardware-accelerated CRC32-C (SSE4.2) with a software fallback.

Buffer Hashing¶

unsigned int libxs_hash(const void* data, unsigned int size,
  unsigned int seed);

Produce a 32-bit hash from a byte buffer of the given size. NULL buffer is accepted (returns seed). Uses CRC32-C when SSE4.2 is available, otherwise a software table-based CRC32.

Fixed-Width Hashing¶

unsigned int libxs_hash8(unsigned int data);
unsigned int libxs_hash16(unsigned int data);
unsigned int libxs_hash32(unsigned long long data);

Hash an 8-, 16-, or 32-bit value. The input is split into a data part and an implicit seed derived from the remaining bits. The result is masked to the corresponding width (8, 16, or 32 bits).

String Hashing¶

unsigned long long libxs_hash_string(const char string[]);

64-bit hash of a character string. Short strings (up to 8 bytes) are stored directly; longer strings use two CRC32 passes combined into a 64-bit result. NULL-string is accepted (returns zero).

CRC32 (ISO 3309)¶

unsigned int libxs_hash_iso3309(const void* data,
  unsigned int size, unsigned int seed);

CRC-32 using the ISO 3309 polynomial (used by PNG, gzip, and similar formats). Software-only, no hardware acceleration. Pre-condition and post-XOR with 0xFFFFFFFF are the caller's responsibility. NULL buffer is accepted.

Adler-32¶

unsigned int libxs_adler32(const void* data,
  unsigned int size, unsigned int seed);

Adler-32 checksum (the variant used by zlib). The standard initial seed is 1. NULL buffer is accepted.