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

     /*
      * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
      *
      * @APPLE_LICENSE_HEADER_START@
      * 
      * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
      * 
      * 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. 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_LICENSE_HEADER_END@
     */
    #include <string.h>
    #if KERNEL
    #include <libsa/mkext.h>
    #include <libsa/stdlib.h>
    #else
    #include <Kernel/libsa/mkext.h>
    #include <stdlib.h>
    #endif /* KERNEL */
    
    
    __private_extern__ u_int32_t
    adler32(u_int8_t *buffer, int32_t length)
    {
        int32_t cnt;
        u_int32_t  result, lowHalf, highHalf;
        
        lowHalf = 1;
        highHalf = 0;
        
        for (cnt = 0; cnt < length; cnt++) {
            if ((cnt % 5000) == 0) {
                lowHalf  %= 65521L;
                highHalf %= 65521L;
            }
            
            lowHalf += buffer[cnt];
            highHalf += lowHalf;
        }
        
        lowHalf  %= 65521L;
        highHalf %= 65521L;
        
        result = (highHalf << 16) | lowHalf;
        
        return result;
    }
    
    /**************************************************************
     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;
    };
    
    
    __private_extern__ int
    decompress_lzss(u_int8_t *dst, 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 *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;
               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;
                   text_buf[r++] = c;
                   r &= (N - 1);
               }
           }
       }
       
       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;
   }
   
   __private_extern__ u_int8_t *
   compress_lzss(u_int8_t *dst, u_int32_t dstlen, u_int8_t *src, u_int32_t srcLen)
   {
       /* Encoding state, mostly tree but some current match stuff */
       struct encode_state *sp;
   
       int  i, c, len, r, s, last_match_length, code_buf_ptr;
       u_int8_t code_buf[17], mask;
       u_int8_t *srcend = src + srcLen;
       u_int8_t *dstend = dst + dstlen;
   
       /* initialize trees */
       sp = (struct encode_state *) malloc(sizeof(*sp));
       init_state(sp);
   
       /*
        * code_buf[1..16] saves eight units of code, and code_buf[0] works
        * as eight flags, "1" representing that the unit is an unencoded
        * letter (1 byte), "" a position-and-length pair (2 bytes).
        * Thus, eight units require at most 16 bytes of code.
        */
       code_buf[0] = 0;
       code_buf_ptr = mask = 1;
   
       /* Clear the buffer with any character that will appear often. */
       s = 0;  r = N - F;
   
       /* Read F bytes into the last F bytes of the buffer */
       for (len = 0; len < F && src < srcend; len++)
           sp->text_buf[r + len] = *src++;  
       if (!len)
           return (void *) 0;  /* text of size zero */
   
       /*
        * Insert the F strings, each of which begins with one or more
        * 'space' characters.  Note the order in which these strings are
        * inserted.  This way, degenerate trees will be less likely to occur.
        */
       for (i = 1; i <= F; i++)
           insert_node(sp, r - i); 
   
       /*
        * Finally, insert the whole string just read.
        * The global variables match_length and match_position are set.
        */
       insert_node(sp, r);
       do {
           /* match_length may be spuriously long near the end of text. */
           if (sp->match_length > len)
               sp->match_length = len;
           if (sp->match_length <= THRESHOLD) {
               sp->match_length = 1;  /* Not long enough match.  Send one byte. */
               code_buf[0] |= mask;  /* 'send one byte' flag */
               code_buf[code_buf_ptr++] = sp->text_buf[r];  /* Send uncoded. */
           } else {
               /* Send position and length pair. Note match_length > THRESHOLD. */
               code_buf[code_buf_ptr++] = (u_int8_t) sp->match_position;
               code_buf[code_buf_ptr++] = (u_int8_t)
                   ( ((sp->match_position >> 4) & 0xF0)
                   |  (sp->match_length - (THRESHOLD + 1)) );
           }
           if ((mask <<= 1) == 0) {  /* Shift mask left one bit. */
                   /* Send at most 8 units of code together */
               for (i = 0; i < code_buf_ptr; i++)
                   if (dst < dstend)
                       *dst++ = code_buf[i]; 
                   else
                       return (void *) 0;
               code_buf[0] = 0;
               code_buf_ptr = mask = 1;
           }
           last_match_length = sp->match_length;
           for (i = 0; i < last_match_length && src < srcend; i++) {
               delete_node(sp, s);    /* Delete old strings and */
               c = *src++;
               sp->text_buf[s] = c;    /* read new bytes */
   
               /*
                * If the position is near the end of buffer, extend the buffer
                * to make string comparison easier.
                */
               if (s < F - 1)
                   sp->text_buf[s + N] = c;
   
               /* Since this is a ring buffer, increment the position modulo N. */
               s = (s + 1) & (N - 1);
               r = (r + 1) & (N - 1);
   
               /* Register the string in text_buf[r..r+F-1] */
               insert_node(sp, r); 
           }
           while (i++ < last_match_length) {
           delete_node(sp, s);
   
               /* After the end of text, no need to read, */
               s = (s + 1) & (N - 1); 
               r = (r + 1) & (N - 1);
               /* but buffer may not be empty. */
               if (--len)
                   insert_node(sp, r);
           }
       } while (len > 0);   /* until length of string to be processed is zero */
   
       if (code_buf_ptr > 1) {    /* Send remaining code. */
           for (i = 0; i < code_buf_ptr; i++)
               if (dst < dstend)
                   *dst++ = code_buf[i]; 
               else
                   return (void *) 0;
       }
   
       return dst;
   }
   
   #endif /* !KERNEL */
   

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