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Reusing some values in bignum mul.

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This commit is contained in:
Alex Shinn 2014-01-05 08:00:02 -05:00
parent 894d3c5451
commit f1927e5834
1 changed files with 8 additions and 7 deletions
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15
bignum.c
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@ -394,15 +394,16 @@ sexp sexp_bignum_add (sexp ctx, sexp dst, sexp a, sexp b) {
sexp sexp_bignum_sub (sexp ctx, sexp dst, sexp a, sexp b) {
sexp res;
int sign;
if (sexp_bignum_sign(a) == sexp_bignum_sign(b)) {
res = sexp_bignum_sub_digits(ctx, dst, a, b);
sexp_bignum_sign(res)
= (sexp_bignum_compare_abs(a, b) >= 0 ? sexp_bignum_sign(a)
sign = (sexp_bignum_compare_abs(a, b) >= 0 ? sexp_bignum_sign(a)
: -sexp_bignum_sign(a));
res = sexp_bignum_sub_digits(ctx, dst, a, b);
} else {
sign = sexp_bignum_sign(a);
res = sexp_bignum_add_digits(ctx, dst, a, b);
sexp_bignum_sign(res) = sexp_bignum_sign(a);
}
sexp_bignum_sign(res) = sign;
return res;
}
@ -434,7 +435,7 @@ sexp sexp_bignum_mul (sexp ctx, sexp dst, sexp a, sexp b) {
sexp_gc_var7(a0, a1, b0, b1, z0, z1, z2);
if (alen < blen) return sexp_bignum_mul(ctx, dst, b, a);
if (blen == 1) {
z1 = sexp_bignum_fxmul(ctx, NULL, a, bdata[0], 0);
z1 = sexp_bignum_fxmul(ctx, dst, a, bdata[0], 0);
} else {
/* karatsuba: */
/* ab = (a1B^k + a0) * (b1B^k + b0) */
@ -458,8 +459,8 @@ sexp sexp_bignum_mul (sexp ctx, sexp dst, sexp a, sexp b) {
z1 = sexp_bignum_sub(ctx, NULL, z1, z2);
z2 = sexp_bignum_shift(ctx, z2, 2*k);
z1 = sexp_bignum_shift(ctx, z1, k);
z1 = sexp_bignum_add(ctx, NULL, z1, z0);
z1 = sexp_bignum_add(ctx, NULL, z1, z2);
z1 = sexp_bignum_add(ctx, z1, z1, z0);
z1 = sexp_bignum_add(ctx, z1, z1, z2);
sexp_gc_release7(ctx);
}
sexp_bignum_sign(z1) = sexp_bignum_sign(a) * sexp_bignum_sign(b);