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vm: some fixes to fast bignum gcd.

db4
John Benediktsson 2012-08-03 12:13:46 -07:00
parent a4a62524b3
commit 37001708cd
1 changed files with 13 additions and 19 deletions
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32
vm/bignum.cpp
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@ -1768,10 +1768,10 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
{
GC_BIGNUM(a);
GC_BIGNUM(b);
bignum *c, *d, *e, *f, *g;
bignum *c, *d, *e;
bignum_twodigit_type x, y, q, s, t, A, B, C, D;
int nbits, k;
bignum_length_type size_a, size_b;
bignum_length_type size_a, size_b, size_d;
bignum_digit_type *scan_a, *scan_b, *scan_c, *scan_d, *a_end, *b_end;
/* clone the bignums so we can modify them in-place */
@ -1797,8 +1797,11 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
/* Initial reduction: make sure that 0 <= b <= a. */
if (bignum_compare(a, b) == bignum_comparison_less) {
d = a;
size_d = size_a;
a = b;
size_a = size_b;
b = d;
size_b = size_d;
}
while (size_a > 1) {
@ -1832,21 +1835,17 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
if (k == 0) {
/* no progress; do a Euclidean step */
if (BIGNUM_LENGTH (b) == 0) {
if (size_b == 0) {
return a;
}
e = bignum_trim (a);
e = bignum_remainder (a, b);
GC_BIGNUM(e);
f = bignum_trim (b);
GC_BIGNUM(f);
g = bignum_remainder (e, f);
GC_BIGNUM(g);
if (g == BIGNUM_OUT_OF_BAND) {
return g;
if (e == BIGNUM_OUT_OF_BAND) {
return e;
}
a = b;
size_a = BIGNUM_LENGTH (a);
b = g;
size_a = size_b;
b = e;
size_b = BIGNUM_LENGTH (b);
continue;
}
@ -1907,14 +1906,9 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
while (size_b > 0 && *(--scan_b) == 0) size_b--;
}
e = bignum_trim (a);
GC_BIGNUM(e);
f = bignum_trim (b);
GC_BIGNUM(f);
/* a fits into a fixnum, so b must too */
fixnum xx = bignum_to_fixnum (e);
fixnum yy = bignum_to_fixnum (f);
fixnum xx = bignum_to_fixnum (a);
fixnum yy = bignum_to_fixnum (b);
fixnum tt;
/* usual Euclidean algorithm for longs */