view Discovery/Src/crcmodel.c @ 539:d784f281833a

Added inertia simulation for compass heading: In previous version calculated compass values were directly used for visualization of the compass. This causes a fast changing (jumping) of values. With the inertia introduction the compass behalfs more like an analog compass. The final value is reached slowly and the displayed values are more stable. For configuration a new menu item has been added to the compass menu allowing to switch inertia off (default), small and large inertia simulation
author Ideenmodellierer
date Sat, 10 Oct 2020 16:59:18 +0200
parents 5f11787b4f42
children
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/******************************************************************************/
/*                             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                              */
/******************************************************************************/