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113 lines
2.6 KiB
C
113 lines
2.6 KiB
C
/*
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Copyright (C) 2005 MySQL AB
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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USA
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*/
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/*
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Variable length encoding.
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A method to store an arbitrary-size non-negative integer. We let the
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most significant bit of the number indicate that the next byte
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should be contatenated to form the real number.
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*/
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#include "my_vle.h"
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/*
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Function to encode an unsigned long as VLE. The bytes for the VLE
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will be written to the location pointed to by 'out'. The maximum
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number of bytes written will be 'max'.
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PARAMETERS
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out Pointer to beginning of where to store VLE bytes.
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max Maximum number of bytes to write.
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n Number to encode.
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RETURN VALUE
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On success, one past the end of the array containing the VLE
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bytes. On failure, the 'out' pointer is returned.
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*/
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byte*
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my_vle_encode(byte* out, my_size_t max, ulong n)
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{
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byte buf[my_vle_sizeof(n)];
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byte *ptr= buf;
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my_size_t len;
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do
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{
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*ptr++= (n & 0x7F);
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n>>= 7;
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}
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while (n > 0);
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len= ptr - buf;
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if (len <= max)
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{
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/*
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The bytes are stored in reverse order in 'buf'. Let's write them
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in correct order to the output buffer and set the MSB at the
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same time.
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*/
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while (ptr-- > buf)
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{
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byte v= *ptr;
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if (ptr > buf)
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v|= 0x80;
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*out++= v;
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}
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}
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return out;
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}
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/*
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Function to decode a VLE representation of an integral value.
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PARAMETERS
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result_ptr Pointer to an unsigned long where the value will be written.
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vle Pointer to the VLE bytes.
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RETURN VALUE
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One-past the end of the VLE bytes. The routine will never read
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more than sizeof(*result_ptr) + 1 bytes.
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*/
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byte const*
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my_vle_decode(ulong *result_ptr, byte const *vle)
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{
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ulong result= 0;
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my_size_t cnt= 1;
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do
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{
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result<<= 7;
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result|= (*vle & 0x7F);
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}
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while ((*vle++ & 0x80) && ++cnt <= sizeof(*result_ptr) + 1);
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if (cnt <= sizeof(*result_ptr) + 1)
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*result_ptr= result;
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return vle;
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}
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