### view libtommath/bn_mp_div_d.c @ 763:f744321ac048ecc

ecdh works against OpenSSH
author Matt Johnston Mon, 08 Apr 2013 23:12:20 +0800 5ff8218bcee9 60fc6476e044
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```#include <tommath.h>
#ifdef BN_MP_DIV_D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://math.libtomcrypt.com
*/

static int s_is_power_of_two(mp_digit b, int *p)
{
int x;

for (x = 1; x < DIGIT_BIT; x++) {
if (b == (((mp_digit)1)<<x)) {
*p = x;
return 1;
}
}
return 0;
}

/* single digit division (based on routine from MPI) */
int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d)
{
mp_int  q;
mp_word w;
mp_digit t;
int     res, ix;

/* cannot divide by zero */
if (b == 0) {
return MP_VAL;
}

/* quick outs */
if (b == 1 || mp_iszero(a) == 1) {
if (d != NULL) {
*d = 0;
}
if (c != NULL) {
return mp_copy(a, c);
}
return MP_OKAY;
}

/* power of two ? */
if (s_is_power_of_two(b, &ix) == 1) {
if (d != NULL) {
*d = a->dp[0] & ((((mp_digit)1)<<ix) - 1);
}
if (c != NULL) {
return mp_div_2d(a, ix, c, NULL);
}
return MP_OKAY;
}

#ifdef BN_MP_DIV_3_C
/* three? */
if (b == 3) {
return mp_div_3(a, c, d);
}
#endif

/* no easy answer [c'est la vie].  Just division */
if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
return res;
}

q.used = a->used;
q.sign = a->sign;
w = 0;
for (ix = a->used - 1; ix >= 0; ix--) {
w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]);

if (w >= b) {
t = (mp_digit)(w / b);
w -= ((mp_word)t) * ((mp_word)b);
} else {
t = 0;
}
q.dp[ix] = (mp_digit)t;
}

if (d != NULL) {
*d = (mp_digit)w;
}

if (c != NULL) {
mp_clamp(&q);
mp_exch(&q, c);
}
mp_clear(&q);

return res;
}

#endif

/* \$Source: /cvs/libtom/libtommath/bn_mp_div_d.c,v \$ */
/* \$Revision: 1.3 \$ */
/* \$Date: 2006/03/31 14:18:44 \$ */
```