关键词搜索

源码搜索 ×
×

漫话Redis源码之四十八

发布2022-01-02浏览492次

详情内容

这里还是老方法，看核心逻辑，主要就是压缩算法，compress那段是核心。

如果觉得细节难以理解，可以不用过问，不用去细看。反正明白意图即可。

任何人，都不可能熟悉每个细节，对吧！

  1. /*
  2.  * Copyright (c) 2000-2010 Marc Alexander Lehmann <schmorp@schmorp.de>
  3.  *
  4.  * Redistribution and use in source and binary forms, with or without modifica-
  5.  * tion, are permitted provided that the following conditions are met:
  6.  *
  7.  *   1.  Redistributions of source code must retain the above copyright notice,
  8.  *       this list of conditions and the following disclaimer.
  9.  *
  10.  *   2.  Redistributions in binary form must reproduce the above copyright
  11.  *       notice, this list of conditions and the following disclaimer in the
  12.  *       documentation and/or other materials provided with the distribution.
  13.  *
  14.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
  15.  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
  16.  * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
  17.  * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
  18.  * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19.  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
  20.  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  21.  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
  22.  * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  23.  * OF THE POSSIBILITY OF SUCH DAMAGE.
  24.  *
  25.  * Alternatively, the contents of this file may be used under the terms of
  26.  * the GNU General Public License ("GPL") version 2 or any later version,
  27.  * in which case the provisions of the GPL are applicable instead of
  28.  * the above. If you wish to allow the use of your version of this file
  29.  * only under the terms of the GPL and not to allow others to use your
  30.  * version of this file under the BSD license, indicate your decision
  31.  * by deleting the provisions above and replace them with the notice
  32.  * and other provisions required by the GPL. If you do not delete the
  33.  * provisions above, a recipient may use your version of this file under
  34.  * either the BSD or the GPL.
  35.  */
  36.  
  37. #include "lzfP.h"
  38.  
  39. #define HSIZE (1 << (HLOG))
  40.  
  41. /*
  42.  * don't play with this unless you benchmark!
  43.  * the data format is not dependent on the hash function.
  44.  * the hash function might seem strange, just believe me,
  45.  * it works ;)
  46.  */
  47. #ifndef FRST
  48. # define FRST(p) (((p[0]) << 8) | p[1])
  49. # define NEXT(v,p) (((v) << 8) | p[2])
  50. # if ULTRA_FAST
  51. #  define IDX(h) ((( h             >> (3*8 - HLOG)) - h  ) & (HSIZE - 1))
  52. # elif VERY_FAST
  53. #  define IDX(h) ((( h             >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
  54. # else
  55. #  define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
  56. # endif
  57. #endif
  58. /*
  59.  * IDX works because it is very similar to a multiplicative hash, e.g.
  60.  * ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1))
  61.  * the latter is also quite fast on newer CPUs, and compresses similarly.
  62.  *
  63.  * the next one is also quite good, albeit slow ;)
  64.  * (int)(cos(h & 0xffffff) * 1e6)
  65.  */
  66.  
  67. #if 0
  68. /* original lzv-like hash function, much worse and thus slower */
  69. # define FRST(p) (p[0] << 5) ^ p[1]
  70. # define NEXT(v,p) ((v) << 5) ^ p[2]
  71. # define IDX(h) ((h) & (HSIZE - 1))
  72. #endif
  73.  
  74. #define        MAX_LIT        (1 <<  5)
  75. #define        MAX_OFF        (1 << 13)
  76. #define        MAX_REF        ((1 << 8) + (1 << 3))
  77.  
  78. #if __GNUC__ >= 3
  79. # define expect(expr,value)         __builtin_expect ((expr),(value))
  80. # define inline                     inline
  81. #else
  82. # define expect(expr,value)         (expr)
  83. # define inline                     static
  84. #endif
  85.  
  86. #define expect_false(expr) expect ((expr) != 0, 0)
  87. #define expect_true(expr)  expect ((expr) != 0, 1)
  88.  
  89. /*
  90.  * compressed format
  91.  *
  92.  * 000LLLLL <L+1>    ; literal, L+1=1..33 octets
  93.  * LLLooooo oooooooo ; backref L+1=1..7 octets, o+1=1..4096 offset
  94.  * 111ooooo LLLLLLLL oooooooo ; backref L+8 octets, o+1=1..4096 offset
  95.  *
  96.  */
  97.  
  98. unsigned int
  99. lzf_compress (const void *const in_data, unsigned int in_len,
  100. 	      void *out_data, unsigned int out_len
  101. #if LZF_STATE_ARG
  102.               , LZF_STATE htab
  103. #endif
  104.               )
  105. {
  106. #if !LZF_STATE_ARG
  107.   LZF_STATE htab;
  108. #endif
  109.   const u8 *ip = (const u8 *)in_data;
  110.         u8 *op = (u8 *)out_data;
  111.   const u8 *in_end  = ip + in_len;
  112.         u8 *out_end = op + out_len;
  113.   const u8 *ref;
  114.  
  115.   /* off requires a type wide enough to hold a general pointer difference.
  116.    * ISO C doesn't have that (size_t might not be enough and ptrdiff_t only
  117.    * works for differences within a single object). We also assume that no
  118.    * no bit pattern traps. Since the only platform that is both non-POSIX
  119.    * and fails to support both assumptions is windows 64 bit, we make a
  120.    * special workaround for it.
  121.    */
  122. #if defined (WIN32) && defined (_M_X64)
  123.   unsigned _int64 off; /* workaround for missing POSIX compliance */
  124. #else
  125.   unsigned long off;
  126. #endif
  127.   unsigned int hval;
  128.   int lit;
  129.  
  130.   if (!in_len || !out_len)
  131.     return 0;
  132.  
  133. #if INIT_HTAB
  134.   memset (htab, 0, sizeof (htab));
  135. #endif
  136.  
  137.   lit = 0; op++; /* start run */
  138.  
  139.   hval = FRST (ip);
  140.   while (ip < in_end - 2)
  141.     {
  142.       LZF_HSLOT *hslot;
  143.  
  144.       hval = NEXT (hval, ip);
  145.       hslot = htab + IDX (hval);
  146.       ref = *hslot + LZF_HSLOT_BIAS; *hslot = ip - LZF_HSLOT_BIAS;
  147.  
  148.       if (1
  149. #if INIT_HTAB
  150.           && ref < ip /* the next test will actually take care of this, but this is faster */
  151. #endif
  152.           && (off = ip - ref - 1) < MAX_OFF
  153.           && ref > (u8 *)in_data
  154.           && ref[2] == ip[2]
  155. #if STRICT_ALIGN
  156.           && ((ref[1] << 8) | ref[0]) == ((ip[1] << 8) | ip[0])
  157. #else
  158.           && *(u16 *)ref == *(u16 *)ip
  159. #endif
  160.         )
  161.         {
  162.           /* match found at *ref++ */
  163.           unsigned int len = 2;
  164.           unsigned int maxlen = in_end - ip - len;
  165.           maxlen = maxlen > MAX_REF ? MAX_REF : maxlen;
  166.  
  167.           if (expect_false (op + 3 + 1 >= out_end)) /* first a faster conservative test */
  168.             if (op - !lit + 3 + 1 >= out_end) /* second the exact but rare test */
  169.               return 0;
  170.  
  171.           op [- lit - 1] = lit - 1; /* stop run */
  172.           op -= !lit; /* undo run if length is zero */
  173.  
  174.           for (;;)
  175.             {
  176.               if (expect_true (maxlen > 16))
  177.                 {
  178.                   len++; if (ref [len] != ip [len]) break;
  179.                   len++; if (ref [len] != ip [len]) break;
  180.                   len++; if (ref [len] != ip [len]) break;
  181.                   len++; if (ref [len] != ip [len]) break;
  182.  
  183.                   len++; if (ref [len] != ip [len]) break;
  184.                   len++; if (ref [len] != ip [len]) break;
  185.                   len++; if (ref [len] != ip [len]) break;
  186.                   len++; if (ref [len] != ip [len]) break;
  187.  
  188.                   len++; if (ref [len] != ip [len]) break;
  189.                   len++; if (ref [len] != ip [len]) break;
  190.                   len++; if (ref [len] != ip [len]) break;
  191.                   len++; if (ref [len] != ip [len]) break;
  192.  
  193.                   len++; if (ref [len] != ip [len]) break;
  194.                   len++; if (ref [len] != ip [len]) break;
  195.                   len++; if (ref [len] != ip [len]) break;
  196.                   len++; if (ref [len] != ip [len]) break;
  197.                 }
  198.  
  199.               do
  200.                 len++;
  201.               while (len < maxlen && ref[len] == ip[len]);
  202.  
  203.               break;
  204.             }
  205.  
  206.           len -= 2; /* len is now #octets - 1 */
  207.           ip++;
  208.  
  209.           if (len < 7)
  210.             {
  211.               *op++ = (off >> 8) + (len << 5);
  212.             }
  213.           else
  214.             {
  215.               *op++ = (off >> 8) + (  7 << 5);
  216.               *op++ = len - 7;
  217.             }
  218.  
  219.           *op++ = off;
  220.  
  221.           lit = 0; op++; /* start run */
  222.  
  223.           ip += len + 1;
  224.  
  225.           if (expect_false (ip >= in_end - 2))
  226.             break;
  227.  
  228. #if ULTRA_FAST || VERY_FAST
  229.           --ip;
  230. # if VERY_FAST && !ULTRA_FAST
  231.           --ip;
  232. # endif
  233.           hval = FRST (ip);
  234.  
  235.           hval = NEXT (hval, ip);
  236.           htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
  237.           ip++;
  238.  
  239. # if VERY_FAST && !ULTRA_FAST
  240.           hval = NEXT (hval, ip);
  241.           htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
  242.           ip++;
  243. # endif
  244. #else
  245.           ip -= len + 1;
  246.  
  247.           do
  248.             {
  249.               hval = NEXT (hval, ip);
  250.               htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
  251.               ip++;
  252.             }
  253.           while (len--);
  254. #endif
  255.         }
  256.       else
  257.         {
  258.           /* one more literal byte we must copy */
  259.           if (expect_false (op >= out_end))
  260.             return 0;
  261.  
  262.           lit++; *op++ = *ip++;
  263.  
  264.           if (expect_false (lit == MAX_LIT))
  265.             {
  266.               op [- lit - 1] = lit - 1; /* stop run */
  267.               lit = 0; op++; /* start run */
  268.             }
  269.         }
  270.     }
  271.  
  272.   if (op + 3 > out_end) /* at most 3 bytes can be missing here */
  273.     return 0;
  274.  
  275.   while (ip < in_end)
  276.     {
  277.       lit++; *op++ = *ip++;
  278.  
  279.       if (expect_false (lit == MAX_LIT))
  280.         {
  281.           op [- lit - 1] = lit - 1; /* stop run */
  282.           lit = 0; op++; /* start run */
  283.         }
  284.     }
  285.  
  286.   op [- lit - 1] = lit - 1; /* end run */
  287.   op -= !lit; /* undo run if length is zero */
  288.  
  289.   return op - (u8 *)out_data;
  290. }
  291.

相关技术文章

最新源码

下载排行榜
点击QQ咨询
开通会员
返回顶部
×
微信扫码支付 元
微信扫码支付
确定支付下载
请使用微信描二维码支付
×

提示信息

×

选择支付方式

  • 微信支付
  • 支付宝付款
确定支付下载