org.spearce.jgit/src/org/spearce/jgit/util/NB.java

   1 /*
   2  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
   3  *
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or
   7  * without modification, are permitted provided that the following
   8  * conditions are met:
   9  *
  10  * - Redistributions of source code must retain the above copyright
  11  *   notice, this list of conditions and the following disclaimer.
  12  *
  13  * - Redistributions in binary form must reproduce the above
  14  *   copyright notice, this list of conditions and the following
  15  *   disclaimer in the documentation and/or other materials provided
  16  *   with the distribution.
  17  *
  18  * - Neither the name of the Git Development Community nor the
  19  *   names of its contributors may be used to endorse or promote
  20  *   products derived from this software without specific prior
  21  *   written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  24  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  25  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  26  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  28  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  29  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  30  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  31  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  32  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  33  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  34  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  35  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  */
  37
  38 package org.spearce.jgit.util;
  39
  40 import java.io.EOFException;
  41 import java.io.IOException;
  42 import java.io.InputStream;
  43
  44 /** Conversion utilities for network byte order handling. */
  45 public final class NB {
  46         /**
  47          * Read the entire byte array into memory, or throw an exception.
  48          *
  49          * @param fd
  50          *            input stream to read the data from.
  51          * @param dst
  52          *            buffer that must be fully populated, [off, off+len).
  53          * @param off
  54          *            position within the buffer to start writing to.
  55          * @param len
  56          *            number of bytes that must be read.
  57          * @throws EOFException
  58          *             the stream ended before dst was fully populated.
  59          * @throws IOException
  60          *             there was an error reading from the stream.
  61          */
  62         public static void readFully(final InputStream fd, final byte[] dst,
  63                         int off, int len) throws IOException {
  64                 while (len > 0) {
  65                         final int r = fd.read(dst, off, len);
  66                         if (r <= 0)
  67                                 throw new EOFException("Short read of block.");
  68                         off += r;
  69                         len -= r;
  70                 }
  71         }
  72
  73         /**
  74          * Compare a 32 bit unsigned integer stored in a 32 bit signed integer.
  75          * <p>
  76          * This function performs an unsigned compare operation, even though Java
  77          * does not natively support unsigned integer values. Negative numbers are
  78          * treated as larger than positive ones.
  79          *
  80          * @param a
  81          *            the first value to compare.
  82          * @param b
  83          *            the second value to compare.
  84          * @return < 0 if a < b; 0 if a == b; > 0 if a > b.
  85          */
  86         public static int compareUInt32(final int a, final int b) {
  87                 final int cmp = (a >>> 1) - (b >>> 1);
  88                 if (cmp != 0)
  89                         return cmp;
  90                 return (a & 1) - (b & 1);
  91         }
  92
  93         /**
  94          * Convert sequence of 4 bytes (network byte order) into signed value.
  95          *
  96          * @param intbuf
  97          *            buffer to acquire the 4 bytes of data from.
  98          * @param offset
  99          *            position within the buffer to begin reading from. This
 100          *            position and the next 3 bytes after it (for a total of 4
 101          *            bytes) will be read.
 102          * @return signed integer value that matches the 32 bits read.
 103          */
 104         public static int decodeInt32(final byte[] intbuf, final int offset) {
 105                 int r = intbuf[offset] << 8;
 106
 107                 r |= intbuf[offset + 1] & 0xff;
 108                 r <<= 8;
 109
 110                 r |= intbuf[offset + 2] & 0xff;
 111                 return (r << 8) | (intbuf[offset + 3] & 0xff);
 112         }
 113
 114         /**
 115          * Convert sequence of 4 bytes (network byte order) into unsigned value.
 116          *
 117          * @param intbuf
 118          *            buffer to acquire the 4 bytes of data from.
 119          * @param offset
 120          *            position within the buffer to begin reading from. This
 121          *            position and the next 3 bytes after it (for a total of 4
 122          *            bytes) will be read.
 123          * @return unsigned integer value that matches the 32 bits read.
 124          */
 125         public static long decodeUInt32(final byte[] intbuf, final int offset) {
 126                 int low = (intbuf[offset + 1] & 0xff) << 8;
 127                 low |= (intbuf[offset + 2] & 0xff);
 128                 low <<= 8;
 129
 130                 low |= (intbuf[offset + 3] & 0xff);
 131                 return ((long) (intbuf[offset] & 0xff)) << 24 | low;
 132         }
 133
 134         /**
 135          * Convert sequence of 8 bytes (network byte order) into unsigned value.
 136          *
 137          * @param intbuf
 138          *            buffer to acquire the 8 bytes of data from.
 139          * @param offset
 140          *            position within the buffer to begin reading from. This
 141          *            position and the next 7 bytes after it (for a total of 8
 142          *            bytes) will be read.
 143          * @return unsigned integer value that matches the 64 bits read.
 144          */
 145         public static long decodeUInt64(final byte[] intbuf, final int offset) {
 146                 return (decodeUInt32(intbuf, offset) << 32)
 147                                 | decodeUInt32(intbuf, offset + 4);
 148         }
 149
 150         /**
 151          * Write a 32 bit integer as a sequence of 4 bytes (network byte order).
 152          *
 153          * @param intbuf
 154          *            buffer to write the 4 bytes of data into.
 155          * @param offset
 156          *            position within the buffer to begin writing to. This position
 157          *            and the next 3 bytes after it (for a total of 4 bytes) will be
 158          *            replaced.
 159          * @param v
 160          *            the value to write.
 161          */
 162         public static void encodeInt32(final byte[] intbuf, final int offset, int v) {
 163                 intbuf[offset + 3] = (byte) v;
 164                 v >>>= 8;
 165
 166                 intbuf[offset + 2] = (byte) v;
 167                 v >>>= 8;
 168
 169                 intbuf[offset + 1] = (byte) v;
 170                 v >>>= 8;
 171
 172                 intbuf[offset] = (byte) v;
 173         }
 174
 175         private NB() {
 176                 // Don't create instances of a static only utility.
 177         }
 178 }