Mercurial > hg > nginx
diff src/core/ngx_crc32.c @ 793:8d39da951bbd
split ngx_crc32() to short and long version
author | Igor Sysoev <igor@sysoev.ru> |
---|---|
date | Thu, 19 Oct 2006 09:57:49 +0000 |
parents | 50f1741a330a |
children | 45df22906c12 |
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--- a/src/core/ngx_crc32.c +++ b/src/core/ngx_crc32.c @@ -9,13 +9,28 @@ /* - * The code and lookup table are based on the algorithm + * 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. So for short messages + * 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 cycle, but cache misses overhead is bigger than overhead of + * the additional code. For example, ngx_crc32_short() of 16 byte message + * takes half as much CPU clocks than ngx_crc32_long(). */ -uint32_t ngx_crc32_table[] = { +static uint32_t ngx_crc32_table16[] = { + 0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac, + 0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c, + 0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c, + 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c +}; + +uint32_t ngx_crc32_table256[] = { 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, @@ -81,3 +96,33 @@ uint32_t ngx_crc32_table[] = { 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d }; + + +uint32_t *ngx_crc32_table_short = ngx_crc32_table16; + + +ngx_int_t +ngx_crc32_init(ngx_pool_t *pool) +{ + void *p; + + if (((uintptr_t) ngx_crc32_table_short + & ~((uintptr_t) ngx_cacheline_size - 1)) + == (uintptr_t) ngx_crc32_table_short) + { + return NGX_OK; + } + + p = ngx_palloc(pool, 16 * sizeof(uint32_t) + ngx_cacheline_size); + if (p == NULL) { + return NGX_ERROR; + } + + p = ngx_align_ptr(p, ngx_cacheline_size); + + ngx_memcpy(p, ngx_crc32_table16, 16 * sizeof(uint32_t)); + + ngx_crc32_table_short = p; + + return NGX_OK; +}