114 lines
3.2 KiB
C
114 lines
3.2 KiB
C
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis
|
||
|
|
*
|
||
|
|
* LibTomMath is library that provides for multiple-precision
|
||
|
|
* integer arithmetic as well as number theoretic functionality.
|
||
|
|
*
|
||
|
|
* The library is designed directly after the MPI library by
|
||
|
|
* Michael Fromberger but has been written from scratch with
|
||
|
|
* additional optimizations in place.
|
||
|
|
*
|
||
|
|
* The library is free for all purposes without any express
|
||
|
|
* guarantee it works.
|
||
|
|
*
|
||
|
|
* Tom St Denis, tomstdenis@iahu.ca, http://libtommath.iahu.ca
|
||
|
|
*/
|
||
|
|
#include <tommath.h>
|
||
|
|
|
||
|
|
/* Fast (comba) multiplier
|
||
|
|
*
|
||
|
|
* This is the fast column-array [comba] multiplier. It is designed to compute
|
||
|
|
* the columns of the product first then handle the carries afterwards. This
|
||
|
|
* has the effect of making the nested loops that compute the columns very
|
||
|
|
* simple and schedulable on super-scalar processors.
|
||
|
|
*
|
||
|
|
*/
|
||
|
|
int
|
||
|
|
fast_s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs)
|
||
|
|
{
|
||
|
|
int olduse, res, pa, ix;
|
||
|
|
mp_word W[512];
|
||
|
|
|
||
|
|
if (c->alloc < digs) {
|
||
|
|
if ((res = mp_grow (c, digs)) != MP_OKAY) {
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* clear temp buf (the columns) */
|
||
|
|
memset (W, 0, sizeof (mp_word) * digs);
|
||
|
|
|
||
|
|
/* calculate the columns */
|
||
|
|
pa = a->used;
|
||
|
|
for (ix = 0; ix < pa; ix++) {
|
||
|
|
|
||
|
|
/* this multiplier has been modified to allow you to control how many digits
|
||
|
|
* of output are produced. So at most we want to make upto "digs" digits
|
||
|
|
* of output
|
||
|
|
*/
|
||
|
|
|
||
|
|
|
||
|
|
/* this adds products to distinct columns (at ix+iy) of W
|
||
|
|
* note that each step through the loop is not dependent on
|
||
|
|
* the previous which means the compiler can easily unroll
|
||
|
|
* the loop without scheduling problems
|
||
|
|
*/
|
||
|
|
{
|
||
|
|
register mp_digit tmpx, *tmpy;
|
||
|
|
register mp_word *_W;
|
||
|
|
register int iy, pb;
|
||
|
|
|
||
|
|
/* alias for the the word on the left e.g. A[ix] * A[iy] */
|
||
|
|
tmpx = a->dp[ix];
|
||
|
|
|
||
|
|
/* alias for the right side */
|
||
|
|
tmpy = b->dp;
|
||
|
|
|
||
|
|
/* alias for the columns, each step through the loop adds a new
|
||
|
|
term to each column
|
||
|
|
*/
|
||
|
|
_W = W + ix;
|
||
|
|
|
||
|
|
/* the number of digits is limited by their placement. E.g.
|
||
|
|
we avoid multiplying digits that will end up above the # of
|
||
|
|
digits of precision requested
|
||
|
|
*/
|
||
|
|
pb = MIN (b->used, digs - ix);
|
||
|
|
|
||
|
|
for (iy = 0; iy < pb; iy++) {
|
||
|
|
*_W++ += ((mp_word) tmpx) * ((mp_word) * tmpy++);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
/* setup dest */
|
||
|
|
olduse = c->used;
|
||
|
|
c->used = digs;
|
||
|
|
|
||
|
|
|
||
|
|
/* At this point W[] contains the sums of each column. To get the
|
||
|
|
* correct result we must take the extra bits from each column and
|
||
|
|
* carry them down
|
||
|
|
*
|
||
|
|
* Note that while this adds extra code to the multiplier it saves time
|
||
|
|
* since the carry propagation is removed from the above nested loop.
|
||
|
|
* This has the effect of reducing the work from N*(N+N*c)==N^2 + c*N^2 to
|
||
|
|
* N^2 + N*c where c is the cost of the shifting. On very small numbers
|
||
|
|
* this is slower but on most cryptographic size numbers it is faster.
|
||
|
|
*/
|
||
|
|
|
||
|
|
for (ix = 1; ix < digs; ix++) {
|
||
|
|
W[ix] += (W[ix - 1] >> ((mp_word) DIGIT_BIT));
|
||
|
|
c->dp[ix - 1] = (mp_digit) (W[ix - 1] & ((mp_word) MP_MASK));
|
||
|
|
}
|
||
|
|
c->dp[digs - 1] = (mp_digit) (W[digs - 1] & ((mp_word) MP_MASK));
|
||
|
|
|
||
|
|
/* clear unused */
|
||
|
|
for (; ix < olduse; ix++) {
|
||
|
|
c->dp[ix] = 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
mp_clamp (c);
|
||
|
|
return MP_OKAY;
|
||
|
|
}
|