core: Add code to read/write "varints"
Adapted from Google protobufs. For several cases, we want to support e.g. file sizes up to guint64, but paying the cost of 8 bytes for each number is too high. This will be used for static deltas and sizes metadata.
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Colin Walters committed
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@@ -0,0 +1,183 @@
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/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
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*
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* Copyright (C) 2013 Colin Walters <walters@verbum.org>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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/* Significant code derived from protobuf: */
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/*
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* Protocol Buffers - Google's data interchange format
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* Copyright 2008 Google Inc. All rights reserved.
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* http: *code.google.com/p/protobuf/
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following disclaimer
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* in the documentation and/or other materials provided with the
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* distribution.
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* * Neither the name of Google Inc. nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "config.h"
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#include "ostree-varint.h"
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static const int max_varint_bytes = 10;
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/**
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* _ostree_read_varuint64:
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* @buf: (array length=buflen): Byte buffer
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* @buflen: Length of bytes in @buf
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* @bytes_read: (out): Number of bytes read
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*
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* Returns: An unsigned 64 bit integer value
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*/
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guint64
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_ostree_read_varuint64 (const guint8 *buf,
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gsize buflen,
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gsize *bytes_read)
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{
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guint64 result = 0;
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int count = 0;
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guint8 b;
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/* Adapted from CodedInputStream::ReadVarint64Slow */
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do
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{
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if (count == max_varint_bytes)
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return FALSE;
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if (buflen == 0)
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return FALSE;
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b = *buf;
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result |= ((guint64)(b & 0x7F)) << (7 * count);
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buf++;
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buflen--;
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++count;
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} while (b & 0x80);
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*bytes_read = count;
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return result;
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}
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/**
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* _ostree_write_varuint64:
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* @buf: Target buffer (will contain binary data)
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* @n: Integer to encode
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*
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* Append a varint-encoded version of @n to @buf.
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*/
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void
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_ostree_write_varuint64 (GString *buf, guint64 n)
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{
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/* Splitting into 32-bit pieces gives better performance on 32-bit
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* processors. */
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guint32 part0 = (guint32)n;
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guint32 part1 = (guint32)(n >> 28);
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guint32 part2 = (guint32)(n >> 56);
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guint8 target[10];
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int i;
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int size;
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/*
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* Here we can't really optimize for small numbers, since the value is
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* split into three parts. Cheking for numbers < 128, for instance,
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* would require three comparisons, since you'd have to make sure part1
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* and part2 are zero. However, if the caller is using 64-bit integers,
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* it is likely that they expect the numbers to often be very large, so
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* we probably don't want to optimize for small numbers anyway. Thus,
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* we end up with a hardcoded binary search tree...
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*/
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if (part2 == 0) {
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if (part1 == 0) {
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if (part0 < (1 << 14)) {
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if (part0 < (1 << 7)) {
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size = 1; goto size1;
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} else {
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size = 2; goto size2;
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}
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} else {
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if (part0 < (1 << 21)) {
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size = 3; goto size3;
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} else {
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size = 4; goto size4;
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}
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}
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} else {
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if (part1 < (1 << 14)) {
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if (part1 < (1 << 7)) {
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size = 5; goto size5;
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} else {
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size = 6; goto size6;
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}
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} else {
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if (part1 < (1 << 21)) {
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size = 7; goto size7;
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} else {
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size = 8; goto size8;
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}
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}
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}
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} else {
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if (part2 < (1 << 7)) {
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size = 9; goto size9;
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} else {
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size = 10; goto size10;
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}
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}
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g_assert_not_reached ();
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size10: target[9] = (guint8)((part2 >> 7) | 0x80);
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size9 : target[8] = (guint8)((part2 ) | 0x80);
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size8 : target[7] = (guint8)((part1 >> 21) | 0x80);
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size7 : target[6] = (guint8)((part1 >> 14) | 0x80);
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size6 : target[5] = (guint8)((part1 >> 7) | 0x80);
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size5 : target[4] = (guint8)((part1 ) | 0x80);
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size4 : target[3] = (guint8)((part0 >> 21) | 0x80);
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size3 : target[2] = (guint8)((part0 >> 14) | 0x80);
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size2 : target[1] = (guint8)((part0 >> 7) | 0x80);
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size1 : target[0] = (guint8)((part0 ) | 0x80);
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target[size-1] &= 0x7F;
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for (i = 0; i < size; i++)
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g_string_append_c (buf, target[i]);
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}
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@@ -0,0 +1,34 @@
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/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
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*
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* Copyright (C) 2013 Colin Walters <walters@verbum.org>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#pragma once
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#include <gio/gio.h>
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G_BEGIN_DECLS
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guint64 _ostree_read_varuint64 (const guint8 *buf,
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gsize buflen,
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gsize *bytes_read);
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void _ostree_write_varuint64 (GString *buf, guint64 n);
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G_END_DECLS
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