#include "tommath_private.h" #ifdef BN_FAST_S_MP_SQR_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 * additional optimizations in place. * * SPDX-License-Identifier: Unlicense */ /* the jist of squaring... * you do like mult except the offset of the tmpx [one that * starts closer to zero] can't equal the offset of tmpy. * So basically you set up iy like before then you min it with * (ty-tx) so that it never happens. You double all those * you add in the inner loop After that loop you do the squares and add them in. */ int fast_s_mp_sqr(const mp_int *a, mp_int *b) { int olduse, res, pa, ix, iz; mp_digit W[MP_WARRAY], *tmpx; mp_word W1; /* grow the destination as required */ pa = a->used + a->used; if (b->alloc < pa) { if ((res = mp_grow(b, pa)) != MP_OKAY) { return res; } } /* number of output digits to produce */ W1 = 0; for (ix = 0; ix < pa; ix++) { int tx, ty, iy; mp_word _W; mp_digit *tmpy; /* clear counter */ _W = 0; /* get offsets into the two bignums */ ty = MIN(a->used-1, ix); tx = ix - ty; /* setup temp aliases */ tmpx = a->dp + tx; tmpy = a->dp + ty; /* this is the number of times the loop will iterrate, essentially while (tx++ < a->used && ty-- >= 0) { ... } */ iy = MIN(a->used-tx, ty+1); /* now for squaring tx can never equal ty * we halve the distance since they approach at a rate of 2x * and we have to round because odd cases need to be executed */ iy = MIN(iy, ((ty-tx)+1)>>1); /* execute loop */ for (iz = 0; iz < iy; iz++) { _W += (mp_word)*tmpx++ * (mp_word)*tmpy--; } /* double the inner product and add carry */ _W = _W + _W + W1; /* even columns have the square term in them */ if (((unsigned)ix & 1u) == 0u) { _W += (mp_word)a->dp[ix>>1] * (mp_word)a->dp[ix>>1]; } /* store it */ W[ix] = _W & MP_MASK; /* make next carry */ W1 = _W >> (mp_word)DIGIT_BIT; } /* setup dest */ olduse = b->used; b->used = a->used+a->used; { mp_digit *tmpb; tmpb = b->dp; for (ix = 0; ix < pa; ix++) { *tmpb++ = W[ix] & MP_MASK; } /* clear unused digits [that existed in the old copy of c] */ for (; ix < olduse; ix++) { *tmpb++ = 0; } } mp_clamp(b); return MP_OKAY; } #endif /* ref: HEAD -> master, tag: v1.1.0 */ /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ /* commit time: 2019-01-28 20:32:32 +0100 */