/******************************************************************************/+
−
/*                             Start of crcmodel.c                            */+
−
/******************************************************************************/+
−
/*                                                                            */+
−
/* Author : Ross Williams (ross@guest.adelaide.edu.au.).                      */+
−
/* Date   : 3 June 1993.                                                      */+
−
/* Status : Public domain.                                                    */+
−
/*                                                                            */+
−
/* Description : This is the implementation (.c) file for the reference       */+
−
/* implementation of the Rocksoft^tm Model CRC Algorithm. For more            */+
−
/* information on the Rocksoft^tm Model CRC Algorithm, see the document       */+
−
/* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross        */+
−
/* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in   */+
−
/* "ftp.adelaide.edu.au/pub/rocksoft".                                        */+
−
/*                                                                            */+
−
/* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia.    */+
−
/*                                                                            */+
−
/******************************************************************************/+
−
/*                                                                            */+
−
/* Implementation Notes                                                       */+
−
/* --------------------                                                       */+
−
/* To avoid inconsistencies, the specification of each function is not echoed */+
−
/* here. See the header file for a description of these functions.            */+
−
/* This package is light on checking because I want to keep it short and      */+
−
/* simple and portable (i.e. it would be too messy to distribute my entire    */+
−
/* C culture (e.g. assertions package) with this package.                     */+
−
/*                                                                            */+
−
/******************************************************************************/+
−
+
−
#include "crcmodel.h"+
−
+
−
/******************************************************************************/+
−
+
−
/* The following definitions make the code more readable. */+
−
+
−
#define BITMASK(X) (1L << (X))+
−
#define MASK32 0xFFFFFFFFL+
−
#define LOCAL static+
−
+
−
/******************************************************************************/+
−
+
−
LOCAL ulong reflect P_((ulong v,int b));+
−
LOCAL ulong reflect (ulong v,int b)+
−
/* Returns the value v with the bottom b [0,32] bits reflected. */+
−
/* Example: reflect(0x3e23L,3) == 0x3e26                        */+
−
{+
−
 int   i;+
−
 ulong t = v;+
−
 for (i=0; i<b; i++)+
−
   {+
−
    if (t & 1L)+
−
       v|=  BITMASK((b-1)-i);+
−
    else+
−
       v&= ~BITMASK((b-1)-i);+
−
    t>>=1;+
−
   }+
−
 return v;+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
LOCAL ulong widmask P_((p_cm_t));+
−
LOCAL ulong widmask (p_cm_t p_cm)+
−
/* Returns a longword whose value is (2^p_cm->cm_width)-1.     */+
−
/* The trick is to do this portably (e.g. without doing <<32). */+
−
{+
−
 return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L;+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
void cm_ini (p_cm_t p_cm)+
−
{+
−
 p_cm->cm_reg = p_cm->cm_init;+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
void cm_nxt (p_cm_t p_cm, int ch)+
−
{+
−
 int   i;+
−
 ulong uch  = (ulong) ch;+
−
 ulong topbit = BITMASK(p_cm->cm_width-1);+
−
+
−
 if (p_cm->cm_refin) uch = reflect(uch,8);+
−
 p_cm->cm_reg ^= (uch << (p_cm->cm_width-8));+
−
 for (i=0; i<8; i++)+
−
   {+
−
    if (p_cm->cm_reg & topbit)+
−
       p_cm->cm_reg = (p_cm->cm_reg << 1) ^ p_cm->cm_poly;+
−
    else+
−
       p_cm->cm_reg <<= 1;+
−
    p_cm->cm_reg &= widmask(p_cm);+
−
   }+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
void cm_blk (p_cm_t p_cm,p_ubyte_ blk_adr,ulong blk_len)+
−
{+
−
 while (blk_len--) cm_nxt(p_cm,*blk_adr++);+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
ulong cm_crc (p_cm_t p_cm)+
−
{+
−
 if (p_cm->cm_refot)+
−
    return p_cm->cm_xorot ^ reflect(p_cm->cm_reg,p_cm->cm_width);+
−
 else+
−
    return p_cm->cm_xorot ^ p_cm->cm_reg;+
−
}+
−
+
−
/******************************************************************************/+
−
+
−
ulong cm_tab (p_cm_t p_cm, int index)+
−
{+
−
 int   i;+
−
 ulong r;+
−
 ulong topbit = BITMASK(p_cm->cm_width-1);+
−
 ulong inbyte = (ulong) index;+
−
+
−
 if (p_cm->cm_refin) inbyte = reflect(inbyte,8);+
−
 r = inbyte << (p_cm->cm_width-8);+
−
 for (i=0; i<8; i++)+
−
    if (r & topbit)+
−
       r = (r << 1) ^ p_cm->cm_poly;+
−
    else+
−
       r<<=1;+
−
 if (p_cm->cm_refin) r = reflect(r,p_cm->cm_width);+
−
 return r & widmask(p_cm);+
−
}+
−
+
−
/******************************************************************************/+
−
/*                             End of crcmodel.c                              */+
−
/******************************************************************************/+
−
+
−