inffast.cpp

DES,MD5,ZLIB算法源代码

/* inffast.c -- process literals and length/distance pairs fast
 * Copyright (C) 1995-1998 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "stdafx.h"
#include "zutil.h"
#include "inftrees.h"
#include "infblock.h"
#include "infcodes.h"
#include "infutil.h"
#include "inffast.h"

struct inflate_codes_state {int dummy;}; /* for buggy compilers */

/* simplify the use of the inflate_huft type with some defines */
#define exop word.what.Exop
#define bits word.what.Bits

/* macros for bit input with no checking and for returning unused bytes */
#define GRABBITS(j) {while(k<(j)){b|=((unsigned long)NEXTBYTE)<<k;k+=8;}}
#define UNGRAB {c=z->avail_in-n;c=(k>>3)<c?k>>3:c;n+=c;p-=c;k-=c<<3;}

/* Called with number of bytes left to write in window at least 258
   (the maximum string length) and number of input bytes available
   at least ten.  The ten bytes are six bytes for the longest length/
   distance pair plus four bytes for overloading the bit buffer. */

int inflate_fast(unsigned int bl, unsigned int bd,
inflate_huft *tl,
inflate_huft *td, /* need separate declaration for Borland C++ */
inflate_blocks_statef *s,
z_streamp z)
{
  inflate_huft *t;      /* temporary pointer */
  unsigned int e;               /* extra bits or operation */
  unsigned long b;              /* bit buffer */
  unsigned int k;               /* bits in bit buffer */
  BYTE *p;             /* input data pointer */
  unsigned int n;               /* bytes available there */
  BYTE *q;             /* output window write pointer */
  unsigned int m;               /* bytes to end of window or read pointer */
  unsigned int ml;              /* mask for literal/length tree */
  unsigned int md;              /* mask for distance tree */
  unsigned int c;               /* bytes to copy */
  unsigned int d;               /* distance back to copy from */
  BYTE *r;             /* copy source pointer */

  /* load input, output, bit values */
  LOAD

  /* initialize masks */
  ml = inflate_mask[bl];
  md = inflate_mask[bd];

  /* do until not enough input or output space for fast loop */
  do {                          /* assume called with m >= 258 && n >= 10 */
    /* get literal/length code */
    GRABBITS(20)                /* max bits for literal/length code */
    if ((e = (t = tl + ((unsigned int)b & ml))->exop) == 0)
    {
      DUMPBITS(t->bits)
      *q++ = (BYTE)t->base;
      m--;
      continue;
    }
    do {
      DUMPBITS(t->bits)
      if (e & 16)
      {
        /* get extra bits for length */
        e &= 15;
        c = t->base + ((unsigned int)b & inflate_mask[e]);
        DUMPBITS(e)
        /* decode distance base of block to copy */
        GRABBITS(15);           /* max bits for distance code */
        e = (t = td + ((unsigned int)b & md))->exop;
        do {
          DUMPBITS(t->bits)
          if (e & 16)
          {
            /* get extra bits to add to distance base */
            e &= 15;
            GRABBITS(e)         /* get extra bits (up to 13) */
            d = t->base + ((unsigned int)b & inflate_mask[e]);
            DUMPBITS(e)
            /* do the copy */
            m -= c;
            if ((unsigned int)(q - s->window) >= d)     /* offset before dest */
            {                                   /*  just copy */
              r = q - d;
              *q++ = *r++;  c--;        /* minimum count is three, */
              *q++ = *r++;  c--;        /*  so unroll loop a little */
            }
            else                        /* else offset after destination */
            {
              e = d - (unsigned int)(q - s->window); /* bytes from offset to end */
              r = s->end - e;           /* pointer to offset */
              if (c > e)                /* if source crosses, */
              {
                c -= e;                 /* copy to end of window */
                do {
                  *q++ = *r++;
                } while (--e);
                r = s->window;          /* copy rest from start of window */
              }
            }
            do {                        /* copy all or what's left */
              *q++ = *r++;
            } while (--c);
            break;
          }
          else if ((e & 64) == 0)
          {
            t += t->base;
            e = (t += ((unsigned int)b & inflate_mask[e]))->exop;
          }
          else
          {
            z->msg = (char*)"invalid distance code";
            UNGRAB
            UPDATE
            return Z_DATA_ERROR;
          }
        } while (1);
        break;
      }
      if ((e & 64) == 0)
      {
        t += t->base;
        if ((e = (t += ((unsigned int)b & inflate_mask[e]))->exop) == 0)
        {
          DUMPBITS(t->bits)
          *q++ = (BYTE)t->base;
          m--;
          break;
        }
      }
      else if (e & 32)
      {
        UNGRAB
        UPDATE
        return Z_STREAM_END;
      }
      else
      {
        z->msg = (char*)"invalid literal/length code";
        UNGRAB
        UPDATE
        return Z_DATA_ERROR;
      }
    } while (1);
  } while (m >= 258 && n >= 10);

  /* not enough input or output--restore pointers and return */
  UNGRAB
  UPDATE
  return Z_OK;
}