getbits.h

来自「从 IEEE 1394总线接收传输流」· C头文件 代码 · 共 34 行

/* that's the same file as getits.c but with defines to
  force inlining */

static unsigned long rval;
static unsigned char rval_uc;

#define backbits(nob) ((void)( \
  bsi.bitindex    -= nob, \
  bsi.wordpointer += (bsi.bitindex>>3), \
  bsi.bitindex    &= 0x7 ))

#define getbitoffset() ((-bsi.bitindex)&0x7)
#define getbyte()      (*bsi.wordpointer++)

#define getbits(nob) ( \
  rval = bsi.wordpointer[0], rval <<= 8, rval |= bsi.wordpointer[1], \
  rval <<= 8, rval |= bsi.wordpointer[2], rval <<= bsi.bitindex, \
  rval &= 0xffffff, bsi.bitindex += nob, \
  rval >>= (24-nob), bsi.wordpointer += (bsi.bitindex>>3), \
  bsi.bitindex &= 7,rval)

#define getbits_fast(nob) ( \
  rval = (unsigned char) (bsi.wordpointer[0] << bsi.bitindex), \
  rval |= ((unsigned long) bsi.wordpointer[1]<<bsi.bitindex)>>8, \
  rval <<= nob, rval >>= 8, \
  bsi.bitindex += nob, bsi.wordpointer += (bsi.bitindex>>3), \
  bsi.bitindex &= 7, rval )

#define get1bit() ( \
  rval_uc = *bsi.wordpointer << bsi.bitindex, bsi.bitindex++, \
  bsi.wordpointer += (bsi.bitindex>>3), bsi.bitindex &= 7, rval_uc>>7 )