/home/ntakagi/work/tcl8.5.1/libtommath/bn_mp_radix_size.c Source File

00001 #include <tommath.h>
00002 #ifdef BN_MP_RADIX_SIZE_C
00003 /* LibTomMath, multiple-precision integer library -- Tom St Denis
00004  *
00005  * LibTomMath is a library that provides multiple-precision
00006  * integer arithmetic as well as number theoretic functionality.
00007  *
00008  * The library was designed directly after the MPI library by
00009  * Michael Fromberger but has been written from scratch with
00010  * additional optimizations in place.
00011  *
00012  * The library is free for all purposes without any express
00013  * guarantee it works.
00014  *
00015  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
00016  */
00017 
00018 /* returns size of ASCII reprensentation */
00019 int mp_radix_size (mp_int * a, int radix, int *size)
00020 {
00021   int     res, digs;
00022   mp_int  t;
00023   mp_digit d;
00024 
00025   *size = 0;
00026 
00027   /* special case for binary */
00028   if (radix == 2) {
00029     *size = mp_count_bits (a) + (a->sign == MP_NEG ? 1 : 0) + 1;
00030     return MP_OKAY;
00031   }
00032 
00033   /* make sure the radix is in range */
00034   if (radix < 2 || radix > 64) {
00035     return MP_VAL;
00036   }
00037 
00038   if (mp_iszero(a) == MP_YES) {
00039     *size = 2;
00040     return MP_OKAY;
00041   }
00042 
00043   /* digs is the digit count */
00044   digs = 0;
00045 
00046   /* if it's negative add one for the sign */
00047   if (a->sign == MP_NEG) {
00048     ++digs;
00049   }
00050 
00051   /* init a copy of the input */
00052   if ((res = mp_init_copy (&t, a)) != MP_OKAY) {
00053     return res;
00054   }
00055 
00056   /* force temp to positive */
00057   t.sign = MP_ZPOS; 
00058 
00059   /* fetch out all of the digits */
00060   while (mp_iszero (&t) == MP_NO) {
00061     if ((res = mp_div_d (&t, (mp_digit) radix, &t, &d)) != MP_OKAY) {
00062       mp_clear (&t);
00063       return res;
00064     }
00065     ++digs;
00066   }
00067   mp_clear (&t);
00068 
00069   /* 
00070    * return digs + 1, the 1 is for the NULL byte that would be required.
00071    * mp_toradix_n requires a minimum of 3 bytes, so never report less than
00072    * that.
00073    */
00074 
00075   if ( digs >= 2 ) {
00076       *size = digs + 1;
00077   } else {
00078       *size = 3;
00079   }
00080   return MP_OKAY;
00081 }
00082 
00083 #endif
00084 
00085 /* $Source: /cvsroot/tcl/libtommath/bn_mp_radix_size.c,v $ */
00086 /* Tom's revision is 1.4 */
00087 /* $Revision: 1.5 $ */
00088 /* $Date: 2006/12/01 00:31:32 $ */