codecs/ilbc/packing.c

   1
   2 /******************************************************************
   3
   4     iLBC Speech Coder ANSI-C Source Code
   5
   6     packing.c
   7
   8     Copyright (C) The Internet Society (2004).
   9     All Rights Reserved.
  10
  11 ******************************************************************/
  12
  13 #include <math.h>
  14 #include <stdlib.h>
  15
  16 #include "iLBC_define.h"
  17 #include "constants.h"
  18 #include "helpfun.h"
  19 #include "packing.h"
  20 #include "string.h"
  21
  22 /*----------------------------------------------------------------*
  23  *  splitting an integer into first most significant bits and
  24  *  remaining least significant bits
  25  *---------------------------------------------------------------*/
  26
  27 void packsplit(
  28     int *index,                 /* (i) the value to split */
  29     int *firstpart,             /* (o) the value specified by most
  30                                        significant bits */
  31     int *rest,                  /* (o) the value specified by least
  32                                        significant bits */
  33     int bitno_firstpart,    /* (i) number of bits in most
  34                                        significant part */
  35     int bitno_total             /* (i) number of bits in full range
  36                                        of value */
  37 ){
  38     int bitno_rest = bitno_total-bitno_firstpart;
  39
  40
  41
  42     *firstpart = *index>>(bitno_rest);
  43     *rest = *index-(*firstpart<<(bitno_rest));
  44 }
  45
  46 /*----------------------------------------------------------------*
  47  *  combining a value corresponding to msb's with a value
  48  *  corresponding to lsb's
  49  *---------------------------------------------------------------*/
  50
  51 void packcombine(
  52     int *index,                 /* (i/o) the msb value in the
  53                                        combined value out */
  54     int rest,                   /* (i) the lsb value */
  55     int bitno_rest              /* (i) the number of bits in the
  56                                        lsb part */
  57 ){
  58     *index = *index<<bitno_rest;
  59     *index += rest;
  60 }
  61
  62 /*----------------------------------------------------------------*
  63  *  packing of bits into bitstream, i.e., vector of bytes
  64  *---------------------------------------------------------------*/
  65
  66 void dopack(
  67     unsigned char **bitstream,  /* (i/o) on entrance pointer to
  68                                        place in bitstream to pack
  69                                        new data, on exit pointer
  70                                        to place in bitstream to
  71                                        pack future data */
  72     int index,                  /* (i) the value to pack */
  73     int bitno,                  /* (i) the number of bits that the
  74                                        value will fit within */
  75     int *pos                /* (i/o) write position in the
  76                                        current byte */
  77 ){
  78     int posLeft;
  79
  80     /* Clear the bits before starting in a new byte */
  81
  82     if ((*pos)==0) {
  83         **bitstream=0;
  84     }
  85
  86     while (bitno>0) {
  87
  88         /* Jump to the next byte if end of this byte is reached*/
  89
  90         if (*pos==8) {
  91             *pos=0;
  92             (*bitstream)++;
  93             **bitstream=0;
  94         }
  95
  96
  97
  98         posLeft=8-(*pos);
  99
 100         /* Insert index into the bitstream */
 101
 102         if (bitno <= posLeft) {
 103             **bitstream |= (unsigned char)(index<<(posLeft-bitno));
 104             *pos+=bitno;
 105             bitno=0;
 106         } else {
 107             **bitstream |= (unsigned char)(index>>(bitno-posLeft));
 108
 109             *pos=8;
 110             index-=((index>>(bitno-posLeft))<<(bitno-posLeft));
 111
 112             bitno-=posLeft;
 113         }
 114     }
 115 }
 116
 117 /*----------------------------------------------------------------*
 118  *  unpacking of bits from bitstream, i.e., vector of bytes
 119  *---------------------------------------------------------------*/
 120
 121 void unpack(
 122     unsigned char **bitstream,  /* (i/o) on entrance pointer to
 123                                        place in bitstream to
 124                                        unpack new data from, on
 125                                        exit pointer to place in
 126                                        bitstream to unpack future
 127                                        data from */
 128     int *index,                 /* (o) resulting value */
 129     int bitno,                  /* (i) number of bits used to
 130                                        represent the value */
 131     int *pos                /* (i/o) read position in the
 132                                        current byte */
 133 ){
 134     int BitsLeft;
 135
 136     *index=0;
 137
 138     while (bitno>0) {
 139
 140         /* move forward in bitstream when the end of the
 141            byte is reached */
 142
 143         if (*pos==8) {
 144             *pos=0;
 145             (*bitstream)++;
 146         }
 147
 148         BitsLeft=8-(*pos);
 149
 150         /* Extract bits to index */
 151
 152
 153
 154         if (BitsLeft>=bitno) {
 155             *index+=((((**bitstream)<<(*pos)) & 0xFF)>>(8-bitno));
 156
 157             *pos+=bitno;
 158             bitno=0;
 159         } else {
 160
 161             if ((8-bitno)>0) {
 162                 *index+=((((**bitstream)<<(*pos)) & 0xFF)>>
 163                     (8-bitno));
 164                 *pos=8;
 165             } else {
 166                 *index+=(((int)(((**bitstream)<<(*pos)) & 0xFF))<<
 167                     (bitno-8));
 168                 *pos=8;
 169             }
 170             bitno-=BitsLeft;
 171         }
 172     }
 173 }
 174
 175