nginx/src/core/ngx_crc32.c

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>


/*
 * The code and lookup tables are based on the algorithm
 * described at http://www.w3.org/TR/PNG/
 *
 * The 256 element lookup table takes 1024 bytes, and it may be completely
 * cached after processing about 30-60 bytes of data.  So for short data
 * we use the 16 element lookup table that takes only 64 bytes and align it
 * to CPU cache line size.  Of course, the small table adds code inside
 * CRC32 loop, but the cache misses overhead is bigger than overhead of
 * the additional code.  For example, ngx_crc32_short() of 16 bytes of data
 * takes half as much CPU clocks than ngx_crc32_long().
 */


static uint32_t  ngx_crc32_table16[] = …;


uint32_t  ngx_crc32_table256[] = …;


uint32_t *ngx_crc32_table_short = …;


ngx_int_t
ngx_crc32_table_init(void)
{ … }