u2long.c

在linux系统下开发研究移动通信的工具型代码

/*
 * $Log: u2long.c,v $
 * Revision 1.1  2000/05/03 14:30:04  bjc97r
 * Initial revision
 *
 */
char *_u2long_id = "$Id: u2long.c,v 1.1 2000/05/03 14:30:04 bjc97r Exp $";

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "u2long.h"

/* right shift */
u2long u2long_rshift( u2long *src, unsigned n )
{
  unsigned long temp;
  unsigned long mask;
  unsigned long pos;
  unsigned      i;

  if ( n >= sizeof(unsigned long)*8 ) {
    src->l = src->h;
    src->h = 0;
    n -= sizeof(unsigned long)*8;
    src->l >>= n;
  }
  else {
    src->l >>= n;
    for( mask=0, pos=1, i=0; i < n; pos <<=1, i++ ) mask |= pos;
    temp = mask & src->h;
    src->h >>= n;
    temp <<= sizeof(unsigned long)*8 - n;
    src->l |= temp;
  }

  return *src;
}


/* left shift */
u2long u2long_lshift( u2long *src, unsigned n )
{
  unsigned long temp;
  unsigned long mask;
  unsigned long pos;
  unsigned      i;

  if ( n >= sizeof(unsigned long)*8 ) {
    src->h = src->l;
    src->l = 0;
    n -= sizeof(unsigned long)*8;
    src->h <<= n;
  }
  else {
    src->h <<= n;
    pos = 1 << (sizeof(unsigned long) * 8 - 1);
    for( mask=0, i=0; i < n; pos >>= 1, i++ ) mask |= pos;
    temp = mask & src->l;
    src->l <<= n;
    temp >>= sizeof(unsigned long)*8 - n;
    src->h |= temp;
  }

  return *src;
}


/* increment by 1 */
u2long u2long_inc( u2long *src )
{
  if ( src->l == 0xffffffff )
    src->h ++;
  src->l ++;

  return *src;
}


/* decrement by 1 */
u2long u2long_dec( u2long *src )
{
  if ( !src->l )
    src->h --;
  src->l --;

  return *src;
}


/*
 * compare: return either negative, zero or positive integer
 * based on "src1 - src2".
 */
int u2long_cmp( u2long src1, u2long src2 )
{
  int ans;

  if ( src1.h < src2.h ) ans = -1;
  else if ( src1.h > src2.h ) ans = +1;
  else if ( src1.l < src2.l ) ans = -1;
  else if ( src1.l > src2.l ) ans = +1;
  else ans = 0;

  return ans;
}

/*
 * strtou2long() converts a string representation of a primitive polynomial
 * into two unsigned long intergers. The max degree of the polynomails
 * this function can handle is 63. The string should be an octal representaion
 * of the polynomial without leading zero.
 */
u2long strtou2long( char *P )
{
  u2long poly; 
  size_t len;

  while(*P == '0') P++;  /* Remove possible leading zeros. */
  len = strlen( P );  

  /* Convert the string P into two unsigned long. ------------------ */
  if ( (len < 11) || ( (len == 11) && (P[0] < '4'))  ) { /* deg < 32 */
    poly.h = 0;
    poly.l = strtoul( P, NULL, 8 );
  }
  else if ( len == 11 ) { /* deg == 32 */
    char str0[12];
    strncpy( str0, P, 12 );
    str0[0] -= '4';  /* Make the string a valid 32bit unsigned long. */
    poly.h = 1;
    poly.l = strtoul( str0, NULL, 8 );
  }
  else { /* 32 < deg < 64 */
    unsigned int offset; /* string starting offset for lower 32 bits */
    char substr[12];
    offset = len - 11;
    strncpy( substr, P, offset );  substr[offset] = 0; 
    poly.h = strtoul( substr, NULL, 8 ) << 1;
    strncpy( substr, P+offset, 12 );
    if ( substr[0] < '4' )
      poly.l = strtoul( substr, NULL, 8 );
    else {
      poly.h |= 1;
      substr[0] -= '4';
      poly.l = strtoul( substr, NULL, 8 );
    }
  }

  return poly;
}