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          * Skip an entire region of an input stream.
  75          * <p>
  76          * The input stream's position is moved forward by the number of requested
  77          * bytes, discarding them from the input. This method does not return until
  78          * the exact number of bytes requested has been skipped.
  79          *
  80          * @param fd
  81          *            the stream to skip bytes from.
  82          * @param toSkip
  83          *            total number of bytes to be discarded. Must be >= 0.
  84          * @throws EOFException
  85          *             the stream ended before the requested number of bytes were
  86          *             skipped.
  87          * @throws IOException
  88          *             there was an error reading from the stream.
  89          */
  90         public static void skipFully(final InputStream fd, long toSkip)
  91                         throws IOException {
  92                 while (toSkip > 0) {
  93                         final long r = fd.skip(toSkip);
  94                         if (r <= 0)
  95                                 throw new EOFException("Short skip of block");
  96                         toSkip -= r;
  97                 }
  98         }
  99
 100         /**
 101          * Compare a 32 bit unsigned integer stored in a 32 bit signed integer.
 102          * <p>
 103          * This function performs an unsigned compare operation, even though Java
 104          * does not natively support unsigned integer values. Negative numbers are
 105          * treated as larger than positive ones.
 106          *
 107          * @param a
 108          *            the first value to compare.
 109          * @param b
 110          *            the second value to compare.
 111          * @return < 0 if a < b; 0 if a == b; > 0 if a > b.
 112          */
 113         public static int compareUInt32(final int a, final int b) {
 114                 final int cmp = (a >>> 1) - (b >>> 1);
 115                 if (cmp != 0)
 116                         return cmp;
 117                 return (a & 1) - (b & 1);
 118         }
 119
 120         /**
 121          * Convert sequence of 2 bytes (network byte order) into unsigned value.
 122          *
 123          * @param intbuf
 124          *            buffer to acquire the 2 bytes of data from.
 125          * @param offset
 126          *            position within the buffer to begin reading from. This
 127          *            position and the next byte after it (for a total of 2 bytes)
 128          *            will be read.
 129          * @return unsigned integer value that matches the 16 bits read.
 130          */
 131         public static int decodeUInt16(final byte[] intbuf, final int offset) {
 132                 int r = (intbuf[offset] & 0xff) << 8;
 133                 return r | (intbuf[offset + 1] & 0xff);
 134         }
 135
 136         /**
 137          * Convert sequence of 4 bytes (network byte order) into signed value.
 138          *
 139          * @param intbuf
 140          *            buffer to acquire the 4 bytes of data from.
 141          * @param offset
 142          *            position within the buffer to begin reading from. This
 143          *            position and the next 3 bytes after it (for a total of 4
 144          *            bytes) will be read.
 145          * @return signed integer value that matches the 32 bits read.
 146          */
 147         public static int decodeInt32(final byte[] intbuf, final int offset) {
 148                 int r = intbuf[offset] << 8;
 149
 150                 r |= intbuf[offset + 1] & 0xff;
 151                 r <<= 8;
 152
 153                 r |= intbuf[offset + 2] & 0xff;
 154                 return (r << 8) | (intbuf[offset + 3] & 0xff);
 155         }
 156
 157         /**
 158          * Convert sequence of 4 bytes (network byte order) into unsigned value.
 159          *
 160          * @param intbuf
 161          *            buffer to acquire the 4 bytes of data from.
 162          * @param offset
 163          *            position within the buffer to begin reading from. This
 164          *            position and the next 3 bytes after it (for a total of 4
 165          *            bytes) will be read.
 166          * @return unsigned integer value that matches the 32 bits read.
 167          */
 168         public static long decodeUInt32(final byte[] intbuf, final int offset) {
 169                 int low = (intbuf[offset + 1] & 0xff) << 8;
 170                 low |= (intbuf[offset + 2] & 0xff);
 171                 low <<= 8;
 172
 173                 low |= (intbuf[offset + 3] & 0xff);
 174                 return ((long) (intbuf[offset] & 0xff)) << 24 | low;
 175         }
 176
 177         /**
 178          * Convert sequence of 8 bytes (network byte order) into unsigned value.
 179          *
 180          * @param intbuf
 181          *            buffer to acquire the 8 bytes of data from.
 182          * @param offset
 183          *            position within the buffer to begin reading from. This
 184          *            position and the next 7 bytes after it (for a total of 8
 185          *            bytes) will be read.
 186          * @return unsigned integer value that matches the 64 bits read.
 187          */
 188         public static long decodeUInt64(final byte[] intbuf, final int offset) {
 189                 return (decodeUInt32(intbuf, offset) << 32)
 190                                 | decodeUInt32(intbuf, offset + 4);
 191         }
 192
 193         /**
 194          * Write a 16 bit integer as a sequence of 2 bytes (network byte order).
 195          *
 196          * @param intbuf
 197          *            buffer to write the 2 bytes of data into.
 198          * @param offset
 199          *            position within the buffer to begin writing to. This position
 200          *            and the next byte after it (for a total of 2 bytes) will be
 201          *            replaced.
 202          * @param v
 203          *            the value to write.
 204          */
 205         public static void encodeInt16(final byte[] intbuf, final int offset, int v) {
 206                 intbuf[offset + 1] = (byte) v;
 207                 v >>>= 8;
 208
 209                 intbuf[offset] = (byte) v;
 210         }
 211
 212         /**
 213          * Write a 32 bit integer as a sequence of 4 bytes (network byte order).
 214          *
 215          * @param intbuf
 216          *            buffer to write the 4 bytes of data into.
 217          * @param offset
 218          *            position within the buffer to begin writing to. This position
 219          *            and the next 3 bytes after it (for a total of 4 bytes) will be
 220          *            replaced.
 221          * @param v
 222          *            the value to write.
 223          */
 224         public static void encodeInt32(final byte[] intbuf, final int offset, int v) {
 225                 intbuf[offset + 3] = (byte) v;
 226                 v >>>= 8;
 227
 228                 intbuf[offset + 2] = (byte) v;
 229                 v >>>= 8;
 230
 231                 intbuf[offset + 1] = (byte) v;
 232                 v >>>= 8;
 233
 234                 intbuf[offset] = (byte) v;
 235         }
 236
 237         /**
 238          * Write a 64 bit integer as a sequence of 8 bytes (network byte order).
 239          *
 240          * @param intbuf
 241          *            buffer to write the 48bytes of data into.
 242          * @param offset
 243          *            position within the buffer to begin writing to. This position
 244          *            and the next 7 bytes after it (for a total of 8 bytes) will be
 245          *            replaced.
 246          * @param v
 247          *            the value to write.
 248          */
 249         public static void encodeInt64(final byte[] intbuf, final int offset, long v) {
 250                 intbuf[offset + 7] = (byte) v;
 251                 v >>>= 8;
 252
 253                 intbuf[offset + 6] = (byte) v;
 254                 v >>>= 8;
 255
 256                 intbuf[offset + 5] = (byte) v;
 257                 v >>>= 8;
 258
 259                 intbuf[offset + 4] = (byte) v;
 260                 v >>>= 8;
 261
 262                 intbuf[offset + 3] = (byte) v;
 263                 v >>>= 8;
 264
 265                 intbuf[offset + 2] = (byte) v;
 266                 v >>>= 8;
 267
 268                 intbuf[offset + 1] = (byte) v;
 269                 v >>>= 8;
 270
 271                 intbuf[offset] = (byte) v;
 272         }
 273
 274         private NB() {
 275                 // Don't create instances of a static only utility.
 276         }
 277 }