src/runtime/sc-offset.c

   1 /*
   2  * Decoding SC offsets.
   3  */
   4
   5 /*
   6  * This software is part of the SBCL system. See the README file for
   7  * more information.
   8  *
   9  * This software is derived from the CMU CL system, which was
  10  * written at Carnegie Mellon University and released into the
  11  * public domain. The software is in the public domain and is
  12  * provided with absolutely no warranty. See the COPYING and CREDITS
  13  * files for more information.
  14  */
  15
  16 #include "genesis/sc-offset.h"
  17
  18 int
  19 sc_offset_extract_bits(int sc_offset,
  20                        unsigned int bytes_count,
  21                        struct sc_offset_byte* bytes) {
  22     unsigned int result = 0, i = 0, position, size, mask, index = 0;
  23     for (; i < bytes_count; ++i, index += size) {
  24         position = bytes[i].position;
  25         size = bytes[i].size;
  26         mask = (1 << size) - 1;
  27         result |= ((sc_offset >> position) & mask) << index;
  28     }
  29     return result;
  30 }
  31
  32 int
  33 sc_offset_sc_number(int sc_offset) {
  34     return sc_offset_extract_bits
  35         (sc_offset,
  36          sizeof(sc_offset_sc_number_bytes) / sizeof(struct sc_offset_byte),
  37          sc_offset_sc_number_bytes);
  38 }
  39
  40 int
  41 sc_offset_offset(int sc_offset) {
  42     return sc_offset_extract_bits
  43         (sc_offset,
  44          sizeof(sc_offset_offset_bytes) / sizeof(struct sc_offset_byte),
  45          sc_offset_offset_bytes);
  46 }