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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >CRC Functions</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="CRC Algorithms" HREF="services-crc.html"><LINK REL="PREVIOUS" TITLE="CRC Algorithms" HREF="services-crc.html"><LINK REL="NEXT" TITLE="CPU load measurements" HREF="services-cpuload.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="services-crc.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="services-cpuload.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="CRC-FUNCTIONS">Chapter 50. CRC Functions</H1 ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SERVICES-CRC-API">CRC API</H1 ><P >The package implements a number of CRC functions as described below. The API to these functions is in the include file <TT CLASS="FILENAME" >cyg/crc/crc.h</TT >.</P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CRC-API-CYG-POSIX-CRC32">cyg_posix_crc32</H2 ><P >This function implements a 32 bit CRC which is compliant to the POSIX 1008.2 Standard. This is the same as the Linux cksum program.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >cyg_uint32 cyg_posix_crc32(unsigned char * s, int len);</PRE ></TD ></TR ></TABLE ><P >The CRC calculation is run over the data pointed to by <TT CLASS="PARAMETER" ><I >s</I ></TT >, of length <TT CLASS="PARAMETER" ><I >len</I ></TT >. The CRC is returned as an unsigned long.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CRC-API-CYG-CRC32">cyg_crc32</H2 ><P >These functions implement a 32 bit CRC by Gary S. Brown. They use the polynomial X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >cyg_uint32 cyg_crc32(unsigned char * s, int len); cyg_uint32 cyg_crc32_accumulate(cyg_uint32 crc, unsigned char * s, int len);</PRE ></TD ></TR ></TABLE ><P >The CRC calculation is run over the data pointed to by <TT CLASS="PARAMETER" ><I >s</I ></TT >, of length <TT CLASS="PARAMETER" ><I >len</I ></TT >. The CRC is returned as an unsigned long.</P ><P > The CRC can be calculated over data separated into multiple buffers by using the function <TT CLASS="PARAMETER" ><I > cyg_crc32_accumulate()</I ></TT >. The parameter <TT CLASS="PARAMETER" ><I >crc</I ></TT > should be the result from the previous CRC calculation.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CRC-API-CYG-ETHER-CRC32">cyg_ether_crc32</H2 ><P >These functions implement the 32 bit CRC used by the Ethernet FCS word.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >cyg_uint32 cyg_ether_crc32(unsigned char * s, int len); cyg_uint32 cyg_ether_crc32_accumulate(cyg_uint32 crc, unsigned char * s, int len);</PRE ></TD ></TR ></TABLE ><P >The CRC calculation is run over the data pointed to by <TT CLASS="PARAMETER" ><I >s</I ></TT >, of length <TT CLASS="PARAMETER" ><I >len</I ></TT >. The CRC is returned as an unsigned long.</P ><P > The CRC can be calculated over data separated into multiple buffers by using the function <TT CLASS="PARAMETER" ><I > cyg_ether_crc32_accumulate()</I ></TT >. The parameter <TT CLASS="PARAMETER" ><I >crc</I ></TT > should be the result from the previous CRC calculation.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CRC-API-CYG-CRC16">cyg_crc16</H2 ><P >This function implements a 16 bit CRC. It uses the polynomial x^16+x^12+x^5+1.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >cyg_uint16 cyg_crc16(unsigned char * s, int len);</PRE ></TD ></TR ></TABLE ><P >The CRC calculation is run over the data pointed to by <TT CLASS="PARAMETER" ><I >s</I ></TT >, of length <TT CLASS="PARAMETER" ><I >len</I ></TT >. The CRC is returned as an unsigned short.</P ></DIV ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="services-crc.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="services-cpuload.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >CRC Algorithms</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="services-crc.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >CPU load measurements</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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