FreeBSD/Linux Kernel Cross Reference
sys/libkern/mkext.c

     /*
      * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
      *
      * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
      * 
      * This file contains Original Code and/or Modifications of Original Code
      * as defined in and that are subject to the Apple Public Source License
      * Version 2.0 (the 'License'). You may not use this file except in
      * compliance with the License. The rights granted to you under the License
     * may not be used to create, or enable the creation or redistribution of,
     * unlawful or unlicensed copies of an Apple operating system, or to
     * circumvent, violate, or enable the circumvention or violation of, any
     * terms of an Apple operating system software license agreement.
     * 
     * Please obtain a copy of the License at
     * http://www.opensource.apple.com/apsl/ and read it before using this file.
     * 
     * The Original Code and all software distributed under the License are
     * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
     * Please see the License for the specific language governing rights and
     * limitations under the License.
     * 
     * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
     */
    #include <string.h>
    #include <libkern/mkext.h>
    
    #define BASE 65521L /* largest prime smaller than 65536 */
    #define NMAX 5000  
    // NMAX (was 5521) the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
    
    #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
    #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
    #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
    #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
    #define DO16(buf)   DO8(buf,0); DO8(buf,8);
    
    u_int32_t
    mkext_adler32(uint8_t *buf, int32_t len)
    {
        unsigned long s1 = 1; // adler & 0xffff;
        unsigned long s2 = 0; // (adler >> 16) & 0xffff;
        int k;
    
        while (len > 0) {
            k = len < NMAX ? len : NMAX;
            len -= k;
            while (k >= 16) {
                DO16(buf);
                buf += 16;
                k -= 16;
            }
            if (k != 0) do {
                s1 += *buf++;
                s2 += s1;
            } while (--k);
            s1 %= BASE;
            s2 %= BASE;
        }
        return (s2 << 16) | s1;
    }
    
    
    /**************************************************************
     LZSS.C -- A Data Compression Program
    ***************************************************************
        4/6/1989 Haruhiko Okumura
        Use, distribute, and modify this program freely.
        Please send me your improved versions.
            PC-VAN      SCIENCE
            NIFTY-Serve PAF01022
            CompuServe  74050,1022
    
    **************************************************************/
    
    #define N         4096  /* size of ring buffer - must be power of 2 */
    #define F         18    /* upper limit for match_length */
    #define THRESHOLD 2     /* encode string into position and length
                               if match_length is greater than this */
    #define NIL       N     /* index for root of binary search trees */
    
    struct encode_state {
        /*
         * left & right children & parent. These constitute binary search trees.
         */
        int lchild[N + 1], rchild[N + 257], parent[N + 1];
    
        /* ring buffer of size N, with extra F-1 bytes to aid string comparison */
        u_int8_t text_buf[N + F - 1];
    
        /*
         * match_length of longest match.
         * These are set by the insert_node() procedure.
         */
        int match_position, match_length;
    };
   
   
   int
   decompress_lzss(u_int8_t *dst, u_int32_t dstlen, u_int8_t *src, u_int32_t srclen)
   {
       /* ring buffer of size N, with extra F-1 bytes to aid string comparison */
       u_int8_t text_buf[N + F - 1];
       u_int8_t *dststart = dst;
           u_int8_t *dstend = dst + dstlen;
       u_int8_t *srcend = src + srclen;
       int  i, j, k, r, c;
       unsigned int flags;
       
       dst = dststart;
       srcend = src + srclen;
       for (i = 0; i < N - F; i++)
           text_buf[i] = ' ';
       r = N - F;
       flags = 0;
       for ( ; ; ) {
           if (((flags >>= 1) & 0x100) == 0) {
               if (src < srcend) c = *src++; else break;
               flags = c | 0xFF00;  /* uses higher byte cleverly */
           }   /* to count eight */
           if (flags & 1) {
               if (src < srcend) c = *src++; else break;
               *dst++ = c;
                           if (dst >= dstend) {
                                   goto finish;
                           }
               text_buf[r++] = c;
               r &= (N - 1);
           } else {
               if (src < srcend) i = *src++; else break;
               if (src < srcend) j = *src++; else break;
               i |= ((j & 0xF0) << 4);
               j  =  (j & 0x0F) + THRESHOLD;
               for (k = 0; k <= j; k++) {
                   c = text_buf[(i + k) & (N - 1)];
                   *dst++ = c;
                                   if (dst >= dstend) {
                                           goto finish;
                                   }
                   text_buf[r++] = c;
                   r &= (N - 1);
               }
           }
       }
   finish:
       return dst - dststart;
   }
   
   #if !KERNEL
   
   /*
    * initialize state, mostly the trees
    *
    * For i = 0 to N - 1, rchild[i] and lchild[i] will be the right and left 
    * children of node i.  These nodes need not be initialized.  Also, parent[i] 
    * is the parent of node i.  These are initialized to NIL (= N), which stands 
    * for 'not used.'  For i = 0 to 255, rchild[N + i + 1] is the root of the 
    * tree for strings that begin with character i.  These are initialized to NIL. 
    * Note there are 256 trees. */
   static void init_state(struct encode_state *sp)
   {
       int  i;
   
       bzero(sp, sizeof(*sp));
   
       for (i = 0; i < N - F; i++)
           sp->text_buf[i] = ' ';
       for (i = N + 1; i <= N + 256; i++)
           sp->rchild[i] = NIL;
       for (i = 0; i < N; i++)
           sp->parent[i] = NIL;
   }
   
   /*
    * Inserts string of length F, text_buf[r..r+F-1], into one of the trees
    * (text_buf[r]'th tree) and returns the longest-match position and length
    * via the global variables match_position and match_length.
    * If match_length = F, then removes the old node in favor of the new one,
    * because the old one will be deleted sooner. Note r plays double role,
    * as tree node and position in buffer.
    */
   static void insert_node(struct encode_state *sp, int r)
   {
       int  i, p, cmp;
       u_int8_t  *key;
   
       cmp = 1;
       key = &sp->text_buf[r];
       p = N + 1 + key[0];
       sp->rchild[r] = sp->lchild[r] = NIL;
       sp->match_length = 0;
       for ( ; ; ) {
           if (cmp >= 0) {
               if (sp->rchild[p] != NIL)
                   p = sp->rchild[p];
               else {
                   sp->rchild[p] = r; 
                   sp->parent[r] = p;
                   return;
               }
           } else {
               if (sp->lchild[p] != NIL)
                   p = sp->lchild[p];
               else {
                   sp->lchild[p] = r;
                   sp->parent[r] = p;
                   return;
               }
           }
           for (i = 1; i < F; i++) {
               if ((cmp = key[i] - sp->text_buf[p + i]) != 0)
                   break;
           }
           if (i > sp->match_length) {
               sp->match_position = p;
               if ((sp->match_length = i) >= F)
                   break;
           }
       }
       sp->parent[r] = sp->parent[p];
       sp->lchild[r] = sp->lchild[p];
       sp->rchild[r] = sp->rchild[p];
       sp->parent[sp->lchild[p]] = r;
       sp->parent[sp->rchild[p]] = r;
       if (sp->rchild[sp->parent[p]] == p)
           sp->rchild[sp->parent[p]] = r;
       else
           sp->lchild[sp->parent[p]] = r;
       sp->parent[p] = NIL;  /* remove p */
   }
   
   /* deletes node p from tree */
   static void delete_node(struct encode_state *sp, int p)
   {
       int  q;
       
       if (sp->parent[p] == NIL)
           return;  /* not in tree */
       if (sp->rchild[p] == NIL)
           q = sp->lchild[p];
       else if (sp->lchild[p] == NIL)
           q = sp->rchild[p];
       else {
           q = sp->lchild[p];
           if (sp->rchild[q] != NIL) {
               do {
                   q = sp->rchild[q];
               } while (sp->rchild[q] != NIL);
               sp->rchild[sp->parent[q]] = sp->lchild[q];
               sp->parent[sp->lchild[q]] = sp->parent[q];
               sp->lchild[q] = sp->lchild[p];
               sp->parent[sp->lchild[p]] = q;
           }
           sp->rchild[q] = sp->rchild[p];
           sp->parent[sp->rchild[p]] = q;
       }
       sp->parent[q] = sp->parent[p];
       if (sp->rchild[sp->parent[p]] == p)
           sp->rchild[sp->parent[p]] = q;
       else
           sp->lchild[sp->parent[p]] = q;
       sp->parent[p] = NIL;
   }
   
   #endif /* !KERNEL */
   

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