/******************************************************************************//*                             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 (v,b)/* Returns the value v with the bottom b [0,32] bits reflected. *//* Example: reflect(0x3e23L,3) == 0x3e26                        */ulong v;int   b;{ 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)/* Returns a longword whose value is (2^p_cm->cm_width)-1.     *//* The trick is to do this portably (e.g. without doing <<32). */p_cm_t p_cm;{ return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L;}/******************************************************************************/void cm_ini (p_cm)p_cm_t p_cm;{ p_cm->cm_reg = p_cm->cm_init;}/******************************************************************************/void cm_nxt (p_cm,ch)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,blk_adr,blk_len)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)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,index)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                              *//******************************************************************************/