_ Git - BearSSL/blob - src/int/i31_encode.c

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "inner.h"
  26
  27 /* see inner.h */
  28 void
  29 br_i31_encode(void *dst, size_t len, const uint32_t *x)
  30 {
  31         unsigned char *buf;
  32         size_t k, xlen;
  33         uint32_t acc;
  34         int acc_len;
  35
  36         xlen = (x[0] + 31) >> 5;
  37         if (xlen == 0) {
  38                 memset(dst, 0, len);
  39                 return;
  40         }
  41         buf = (unsigned char *)dst + len;
  42         k = 1;
  43         acc = 0;
  44         acc_len = 0;
  45         while (len != 0) {
  46                 uint32_t w;
  47
  48                 w = (k <= xlen) ? x[k] : 0;
  49                 k ++;
  50                 if (acc_len == 0) {
  51                         acc = w;
  52                         acc_len = 31;
  53                 } else {
  54                         uint32_t z;
  55
  56                         z = acc | (w << acc_len);
  57                         acc_len --;
  58                         acc = w >> (31 - acc_len);
  59                         if (len >= 4) {
  60                                 buf -= 4;
  61                                 len -= 4;
  62                                 br_enc32be(buf, z);
  63                         } else {
  64                                 switch (len) {
  65                                 case 3:
  66                                         buf[-3] = (unsigned char)(z >> 16);
  67                                         /* fall through */
  68                                 case 2:
  69                                         buf[-2] = (unsigned char)(z >> 8);
  70                                         /* fall through */
  71                                 case 1:
  72                                         buf[-1] = (unsigned char)z;
  73                                         break;
  74                                 }
  75                                 return;
  76                         }
  77                 }
  78         }
  79 }