/******************************************************************************//* 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 *//******************************************************************************/