.Dd November 8, 2018
.Dt CRC32 3
.Os
.
.Sh NAME
.Nm crc32 ,
.Nm crc32_z ,
.Nm crc32_combine
.Nd update CRC-32 checksum
.
.Sh LIBRARY
.Lb libz
.
.Sh SYNOPSIS
.In zlib.h
.Ft uLong
.Fn crc32 "uLong crc" "const Bytef *buf" "uInt len"
.Ft uLong
.Fn crc32_z "uLong crc" "const Bytef *buf" "z_size_t len"
.Ft uLong
.Fn crc32_combine "uLong crc1" "uLong crc2" "z_off_t len2"
.
.Sh DESCRIPTION
Update a running CRC-32 with the bytes
.Fa "buf[0..len-1]"
and return the updated CRC-32.
If
.Fa buf
is
.Dv Z_NULL ,
this function returns
the required initial value for the CRC.
Pre- and post-conditioning
(one's complement)
is performed within this function
so it shouldn't be done
by the application.
.
.Pp
.Fn crc32_z
is the same as
.Fn crc32 ,
but with a
.Vt size_t
length.
.
.Pp
.Fn crc32_combine
combines two CRC-32 check values into one.
For two sequences of bytes,
.Va seq1
and
.Va seq2
with lengths
.Va len1
and
.Va len2 ,
CRC-32 check values were calculated for each,
.Va crc1
and
.Va crc2 .
.Fn crc32_combine
returns the CRC-32 check value of
.Va seq1
and
.Va seq2
concatenated,
requiring only
.Fa crc1 ,
.Fa crc2 ,
and
.Fa len2 .
.
.Sh EXAMPLES
.Bd -literal -offset indent
uLong crc = crc32(0L, Z_NULL, 0);

while (read_buffer(buffer, length) != EOF) {
	crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();
.Ed
.
.Sh SEE ALSO
.Xr adler32 3