zlib/inffast.c

   1 /* inffast.c -- process literals and length/distance pairs fast
   2  * Copyright (C) 1995-1998 Mark Adler
   3  * For conditions of distribution and use, see copyright notice in zlib.h
   4  */
   5
   6 #include "zutil.h"
   7 #include "inftrees.h"
   8 #include "infblock.h"
   9 #include "infcodes.h"
  10 #include "infutil.h"
  11 #include "inffast.h"
  12
  13 struct inflate_codes_state {int dummy;}; /* for buggy compilers */
  14
  15 /* simplify the use of the inflate_huft type with some defines */
  16 #define exop word.what.Exop
  17 #define bits word.what.Bits
  18
  19 /* macros for bit input with no checking and for returning unused bytes */
  20 #define GRABBITS(j) {while(k<(j)){b|=((uLong)NEXTBYTE)<<k;k+=8;}}
  21 #define UNGRAB {c=z->avail_in-n;c=(k>>3)<c?k>>3:c;n+=c;p-=c;k-=c<<3;}
  22
  23 /* Called with number of bytes left to write in window at least 258
  24    (the maximum string length) and number of input bytes available
  25    at least ten.  The ten bytes are six bytes for the longest length/
  26    distance pair plus four bytes for overloading the bit buffer. */
  27
  28 int inflate_fast(bl, bd, tl, td, s, z)
  29 uInt bl, bd;
  30 inflate_huft *tl;
  31 inflate_huft *td; /* need separate declaration for Borland C++ */
  32 inflate_blocks_statef *s;
  33 z_streamp z;
  34 {
  35   inflate_huft *t;      /* temporary pointer */
  36   uInt e;               /* extra bits or operation */
  37   uLong b;              /* bit buffer */
  38   uInt k;               /* bits in bit buffer */
  39   Bytef *p;             /* input data pointer */
  40   uInt n;               /* bytes available there */
  41   Bytef *q;             /* output window write pointer */
  42   uInt m;               /* bytes to end of window or read pointer */
  43   uInt ml;              /* mask for literal/length tree */
  44   uInt md;              /* mask for distance tree */
  45   uInt c;               /* bytes to copy */
  46   uInt d;               /* distance back to copy from */
  47   Bytef *r;             /* copy source pointer */
  48
  49   /* load input, output, bit values */
  50   LOAD
  51
  52   /* initialize masks */
  53   ml = inflate_mask[bl];
  54   md = inflate_mask[bd];
  55
  56   /* do until not enough input or output space for fast loop */
  57   do {                          /* assume called with m >= 258 && n >= 10 */
  58     /* get literal/length code */
  59     GRABBITS(20)                /* max bits for literal/length code */
  60     if ((e = (t = tl + ((uInt)b & ml))->exop) == 0)
  61     {
  62       DUMPBITS(t->bits)
  63       Tracevv((stderr, t->base >= 0x20 && t->base < 0x7f ?
  64                 "inflate:         * literal '%c'\n" :
  65                 "inflate:         * literal 0x%02x\n", t->base));
  66       *q++ = (Byte)t->base;
  67       m--;
  68       continue;
  69     }
  70     do {
  71       DUMPBITS(t->bits)
  72       if (e & 16)
  73       {
  74         /* get extra bits for length */
  75         e &= 15;
  76         c = t->base + ((uInt)b & inflate_mask[e]);
  77         DUMPBITS(e)
  78         Tracevv((stderr, "inflate:         * length %u\n", c));
  79
  80         /* decode distance base of block to copy */
  81         GRABBITS(15);           /* max bits for distance code */
  82         e = (t = td + ((uInt)b & md))->exop;
  83         do {
  84           DUMPBITS(t->bits)
  85           if (e & 16)
  86           {
  87             /* get extra bits to add to distance base */
  88             e &= 15;
  89             GRABBITS(e)         /* get extra bits (up to 13) */
  90             d = t->base + ((uInt)b & inflate_mask[e]);
  91             DUMPBITS(e)
  92             Tracevv((stderr, "inflate:         * distance %u\n", d));
  93
  94             /* do the copy */
  95             m -= c;
  96             if ((uInt)(q - s->window) >= d)     /* offset before dest */
  97             {                                   /*  just copy */
  98               r = q - d;
  99               *q++ = *r++;  c--;        /* minimum count is three, */
 100               *q++ = *r++;  c--;        /*  so unroll loop a little */
 101             }
 102             else                        /* else offset after destination */
 103             {
 104               e = d - (uInt)(q - s->window); /* bytes from offset to end */
 105               r = s->end - e;           /* pointer to offset */
 106               if (c > e)                /* if source crosses, */
 107               {
 108                 c -= e;                 /* copy to end of window */
 109                 do {
 110                   *q++ = *r++;
 111                 } while (--e);
 112                 r = s->window;          /* copy rest from start of window */
 113               }
 114             }
 115             do {                        /* copy all or what's left */
 116               *q++ = *r++;
 117             } while (--c);
 118             break;
 119           }
 120           else if ((e & 64) == 0)
 121           {
 122             t += t->base;
 123             e = (t += ((uInt)b & inflate_mask[e]))->exop;
 124           }
 125           else
 126           {
 127             z->msg = (char*)"invalid distance code";
 128             UNGRAB
 129             UPDATE
 130             return Z_DATA_ERROR;
 131           }
 132         } while (1);
 133         break;
 134       }
 135       if ((e & 64) == 0)
 136       {
 137         t += t->base;
 138         if ((e = (t += ((uInt)b & inflate_mask[e]))->exop) == 0)
 139         {
 140           DUMPBITS(t->bits)
 141           Tracevv((stderr, t->base >= 0x20 && t->base < 0x7f ?
 142                     "inflate:         * literal '%c'\n" :
 143                     "inflate:         * literal 0x%02x\n", t->base));
 144           *q++ = (Byte)t->base;
 145           m--;
 146           break;
 147         }
 148       }
 149       else if (e & 32)
 150       {
 151         Tracevv((stderr, "inflate:         * end of block\n"));
 152         UNGRAB
 153         UPDATE
 154         return Z_STREAM_END;
 155       }
 156       else
 157       {
 158         z->msg = (char*)"invalid literal/length code";
 159         UNGRAB
 160         UPDATE
 161         return Z_DATA_ERROR;
 162       }
 163     } while (1);
 164   } while (m >= 258 && n >= 10);
 165
 166   /* not enough input or output--restore pointers and return */
 167   UNGRAB
 168   UPDATE
 169   return Z_OK;
 170 }