SDNV.cc

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00001 /*
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00005  * install, copy or use the software.
00006  * 
00007  * Intel Open Source License 
00008  * 
00009  * Copyright (c) 2005 Intel Corporation. All rights reserved. 
00010  * 
00011  * Redistribution and use in source and binary forms, with or without
00012  * modification, are permitted provided that the following conditions are
00013  * met:
00014  * 
00015  *   Redistributions of source code must retain the above copyright
00016  *   notice, this list of conditions and the following disclaimer.
00017  * 
00018  *   Redistributions in binary form must reproduce the above copyright
00019  *   notice, this list of conditions and the following disclaimer in the
00020  *   documentation and/or other materials provided with the distribution.
00021  * 
00022  *   Neither the name of the Intel Corporation nor the names of its
00023  *   contributors may be used to endorse or promote products derived from
00024  *   this software without specific prior written permission.
00025  *  
00026  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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00036  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00037  */
00038 
00039 #include <oasys/debug/DebugUtils.h>
00040 #include <oasys/debug/Log.h>
00041 
00042 #include "SDNV.h"
00043 
00044 namespace dtn {
00045 
00046 int
00047 SDNV::encode(u_int64_t val, u_char* bp, size_t len)
00048 {
00049     u_char* start = bp;
00050 
00051     /*
00052      * Figure out how many bytes we need for the encoding.
00053      */
00054     size_t val_len = 0;
00055     u_int64_t tmp = val;
00056 
00057     do {
00058         tmp = tmp >> 7;
00059         val_len++;
00060     } while (tmp != 0);
00061 
00062     ASSERT(val_len > 0);
00063     ASSERT(val_len <= 10);
00064 
00065     /*
00066      * Make sure we have enough buffer space.
00067      */
00068     if (len < val_len) {
00069         return -1;
00070     }
00071 
00072     /*
00073      * Now advance bp to the last byte and fill it in backwards with
00074      * the value bytes.
00075      */
00076     bp += val_len;
00077     u_char high_bit = 0; // for the last octet
00078     do {
00079         --bp;
00080         *bp = (u_char)(high_bit | (val & 0x7f));
00081         high_bit = (1 << 7); // for all but the last octet
00082         val = val >> 7;
00083     } while (val != 0);
00084 
00085     ASSERT(bp == start);
00086 
00087     return val_len;
00088 }
00089 
00090 size_t
00091 SDNV::encoding_len(u_int64_t val)
00092 {
00093     u_char buf[16];
00094     int ret = encode(val, buf, sizeof(buf));
00095     ASSERT(ret != -1 && ret != 0);
00096     return ret;
00097 }
00098 
00099 int
00100 SDNV::decode(const u_char* bp, size_t len, u_int64_t* val)
00101 {
00102     const u_char* start = bp;
00103     
00104     if (!val) {
00105         return -1;
00106     }
00107 
00108     /*
00109      * Zero out the existing value, then shift in the bytes of the
00110      * encoding one by one until we hit a byte that has a zero
00111      * high-order bit.
00112      */
00113     size_t val_len = 0;
00114     *val = 0;
00115     do {
00116         if (len == 0)
00117             return -1; // buffer too short
00118         
00119         *val = (*val << 7) | (*bp & 0x7f);
00120         ++val_len;
00121         
00122         if ((*bp & (1 << 7)) == 0)
00123             break; // all done;
00124 
00125         ++bp;
00126         --len;
00127     } while (1);
00128 
00129     /*
00130      * Since the spec allows for infinite length values but this
00131      * implementation only handles up to 64 bits, check for overflow.
00132      * Note that the only supportable 10 byte SDNV must store exactly
00133      * one bit in the first byte of the encoding (i.e. the 64'th bit
00134      * of the original value).
00135      */
00136     if ((val_len > 10) || ((val_len == 10) && (*start != 0x81))) {
00137         log_err("/dtn/bundle/sdnv", "overflow value in sdnv!!!");
00138         return -1;
00139     }
00140 
00141     // XXX/demmer shouldn't use -1 as indication of both too short of
00142     // a buffer and of error due to overflow or malformed SDNV since
00143     // callers just assume that they need more data to decode and
00144     // don't really check for errors
00145 
00146     return val_len;
00147 }
00148 
00149 } // namespace dtn

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