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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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><DIV
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><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 &#0042; 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"
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cyg_uint32 cyg_crc32(unsigned char &#0042; s, int len);
cyg_uint32 cyg_crc32_accumulate(cyg_uint32 crc, unsigned char &#0042; 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 &#0042; s, int len);
cyg_uint32 cyg_ether_crc32_accumulate(cyg_uint32 crc, unsigned char &#0042; 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 &#0042; 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
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